/******************************************************************************
 * levellerdataset.cpp,v 1.22
 *
 * Project:  Leveller TER Driver
 * Purpose:  Reader for Leveller TER documents
 * Author:   Ray Gardener, Daylon Graphics Ltd.
 *
 * Portions of this module derived from GDAL drivers by
 * Frank Warmerdam, see http://www.gdal.org
 *
 ******************************************************************************
 * Copyright (c) 2005-2007 Daylon Graphics Ltd.
 * Copyright (c) 2007-2013, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 ****************************************************************************/

#include "gdal_frmts.h"
#include "gdal_pam.h"
#include "gdal_driver.h"
#include "gdal_drivermanager.h"
#include "gdal_openinfo.h"
#include "gdal_cpp_functions.h"
#include "ogr_spatialref.h"

static bool str_equal(const char *_s1, const char *_s2)
{
    return 0 == strcmp(_s1, _s2);
}

/*GDALDataset *LevellerCreateCopy( const char *, GDALDataset *, int, char **,
                                GDALProgressFunc pfnProgress,
                                void * pProgressData );
*/

/************************************************************************/
/* ==================================================================== */
/*                              LevellerDataset                         */
/* ==================================================================== */
/************************************************************************/

constexpr size_t kMaxTagNameLen = 63;

enum
{
    // Leveller coordsys types.
    LEV_COORDSYS_RASTER = 0,
    LEV_COORDSYS_LOCAL,
    LEV_COORDSYS_GEO
};

enum
{
    // Leveller digital axis extent styles.
    LEV_DA_POSITIONED = 0,
    LEV_DA_SIZED,
    LEV_DA_PIXEL_SIZED
};

typedef enum
{
    // Measurement unit IDs, OEM version.
    UNITLABEL_UNKNOWN = 0x00000000,
    UNITLABEL_PIXEL = 0x70780000,
    UNITLABEL_PERCENT = 0x25000000,

    UNITLABEL_RADIAN = 0x72616400,
    UNITLABEL_DEGREE = 0x64656700,
    UNITLABEL_ARCMINUTE = 0x6172636D,
    UNITLABEL_ARCSECOND = 0x61726373,

    UNITLABEL_YM = 0x796D0000,
    UNITLABEL_ZM = 0x7A6D0000,
    UNITLABEL_AM = 0x616D0000,
    UNITLABEL_FM = 0x666D0000,
    UNITLABEL_PM = 0x706D0000,
    UNITLABEL_A = 0x41000000,
    UNITLABEL_NM = 0x6E6D0000,
    UNITLABEL_U = 0x75000000,
    UNITLABEL_UM = 0x756D0000,
    UNITLABEL_PPT = 0x70707400,
    UNITLABEL_PT = 0x70740000,
    UNITLABEL_MM = 0x6D6D0000,
    UNITLABEL_P = 0x70000000,
    UNITLABEL_CM = 0x636D0000,
    UNITLABEL_IN = 0x696E0000,
    UNITLABEL_DFT = 0x64667400,
    UNITLABEL_DM = 0x646D0000,
    UNITLABEL_LI = 0x6C690000,
    UNITLABEL_SLI = 0x736C6900,
    UNITLABEL_SP = 0x73700000,
    UNITLABEL_FT = 0x66740000,
    UNITLABEL_SFT = 0x73667400,
    UNITLABEL_YD = 0x79640000,
    UNITLABEL_SYD = 0x73796400,
    UNITLABEL_M = 0x6D000000,
    UNITLABEL_FATH = 0x66617468,
    UNITLABEL_R = 0x72000000,
    UNITLABEL_RD = UNITLABEL_R,
    UNITLABEL_DAM = 0x64416D00,
    UNITLABEL_DKM = UNITLABEL_DAM,
    UNITLABEL_CH = 0x63680000,
    UNITLABEL_SCH = 0x73636800,
    UNITLABEL_HM = 0x686D0000,
    UNITLABEL_F = 0x66000000,
    UNITLABEL_KM = 0x6B6D0000,
    UNITLABEL_MI = 0x6D690000,
    UNITLABEL_SMI = 0x736D6900,
    UNITLABEL_NMI = 0x6E6D6900,
    UNITLABEL_MEGAM = 0x4D6D0000,
    UNITLABEL_LS = 0x6C730000,
    UNITLABEL_GM = 0x476D0000,
    UNITLABEL_LM = 0x6C6D0000,
    UNITLABEL_AU = 0x41550000,
    UNITLABEL_TM = 0x546D0000,
    UNITLABEL_LHR = 0x6C687200,
    UNITLABEL_LD = 0x6C640000,
    UNITLABEL_PETAM = 0x506D0000,
    UNITLABEL_LY = 0x6C790000,
    UNITLABEL_PC = 0x70630000,
    UNITLABEL_EXAM = 0x456D0000,
    UNITLABEL_KLY = 0x6B6C7900,
    UNITLABEL_KPC = 0x6B706300,
    UNITLABEL_ZETTAM = 0x5A6D0000,
    UNITLABEL_MLY = 0x4D6C7900,
    UNITLABEL_MPC = 0x4D706300,
    UNITLABEL_YOTTAM = 0x596D0000
} UNITLABEL;

typedef struct
{
    const char *pszID;
    double dScale;
    UNITLABEL oemCode;
} measurement_unit;

constexpr double kdays_per_year = 365.25;
constexpr double kdLStoM = 299792458.0;
constexpr double kdLYtoM = kdLStoM * kdays_per_year * 24 * 60 * 60;
constexpr double kdInch = 0.3048 / 12;
constexpr double kPI = M_PI;

constexpr int kFirstLinearMeasureIdx = 9;

static const measurement_unit kUnits[] = {
    {"", 1.0, UNITLABEL_UNKNOWN},
    {"px", 1.0, UNITLABEL_PIXEL},
    {"%", 1.0, UNITLABEL_PERCENT},  // not actually used

    {"rad", 1.0, UNITLABEL_RADIAN},
    {"\xB0", kPI / 180.0, UNITLABEL_DEGREE},  // \xB0 is Unicode degree symbol
    {"d", kPI / 180.0, UNITLABEL_DEGREE},
    {"deg", kPI / 180.0, UNITLABEL_DEGREE},
    {"'", kPI / (60.0 * 180.0), UNITLABEL_ARCMINUTE},
    {"\"", kPI / (3600.0 * 180.0), UNITLABEL_ARCSECOND},

    {"ym", 1.0e-24, UNITLABEL_YM},
    {"zm", 1.0e-21, UNITLABEL_ZM},
    {"am", 1.0e-18, UNITLABEL_AM},
    {"fm", 1.0e-15, UNITLABEL_FM},
    {"pm", 1.0e-12, UNITLABEL_PM},
    {"A", 1.0e-10, UNITLABEL_A},
    {"nm", 1.0e-9, UNITLABEL_NM},
    {"u", 1.0e-6, UNITLABEL_U},
    {"um", 1.0e-6, UNITLABEL_UM},
    {"ppt", kdInch / 72.27, UNITLABEL_PPT},
    {"pt", kdInch / 72.0, UNITLABEL_PT},
    {"mm", 1.0e-3, UNITLABEL_MM},
    {"p", kdInch / 6.0, UNITLABEL_P},
    {"cm", 1.0e-2, UNITLABEL_CM},
    {"in", kdInch, UNITLABEL_IN},
    {"dft", 0.03048, UNITLABEL_DFT},
    {"dm", 0.1, UNITLABEL_DM},
    {"li", 0.2011684 /* GDAL 0.20116684023368047 ? */, UNITLABEL_LI},
    {"sli", 0.201168402336805, UNITLABEL_SLI},
    {"sp", 0.2286, UNITLABEL_SP},
    {"ft", 0.3048, UNITLABEL_FT},
    {"sft", 1200.0 / 3937.0, UNITLABEL_SFT},
    {"yd", 0.9144, UNITLABEL_YD},
    {"syd", 0.914401828803658, UNITLABEL_SYD},
    {"m", 1.0, UNITLABEL_M},
    {"fath", 1.8288, UNITLABEL_FATH},
    {"rd", 5.02921, UNITLABEL_RD},
    {"dam", 10.0, UNITLABEL_DAM},
    {"dkm", 10.0, UNITLABEL_DKM},
    {"ch", 20.1168 /* GDAL: 2.0116684023368047 ? */, UNITLABEL_CH},
    {"sch", 20.1168402336805, UNITLABEL_SCH},
    {"hm", 100.0, UNITLABEL_HM},
    {"f", 201.168, UNITLABEL_F},
    {"km", 1000.0, UNITLABEL_KM},
    {"mi", 1609.344, UNITLABEL_MI},
    {"smi", 1609.34721869444, UNITLABEL_SMI},
    {"nmi", 1853.0, UNITLABEL_NMI},
    {"Mm", 1.0e+6, UNITLABEL_MEGAM},
    {"ls", kdLStoM, UNITLABEL_LS},
    {"Gm", 1.0e+9, UNITLABEL_GM},
    {"lm", kdLStoM * 60, UNITLABEL_LM},
    {"AU", 8.317 * kdLStoM * 60, UNITLABEL_AU},
    {"Tm", 1.0e+12, UNITLABEL_TM},
    {"lhr", 60.0 * 60.0 * kdLStoM, UNITLABEL_LHR},
    {"ld", 24 * 60.0 * 60.0 * kdLStoM, UNITLABEL_LD},
    {"Pm", 1.0e+15, UNITLABEL_PETAM},
    {"ly", kdLYtoM, UNITLABEL_LY},
    {"pc", 3.2616 * kdLYtoM, UNITLABEL_PC},
    {"Em", 1.0e+18, UNITLABEL_EXAM},
    {"kly", 1.0e+3 * kdLYtoM, UNITLABEL_KLY},
    {"kpc", 3.2616 * 1.0e+3 * kdLYtoM, UNITLABEL_KPC},
    {"Zm", 1.0e+21, UNITLABEL_ZETTAM},
    {"Mly", 1.0e+6 * kdLYtoM, UNITLABEL_MLY},
    {"Mpc", 3.2616 * 1.0e+6 * kdLYtoM, UNITLABEL_MPC},
    {"Ym", 1.0e+24, UNITLABEL_YOTTAM}};

// ----------------------------------------------------------------

static bool approx_equal(double a, double b)
{
    const double epsilon = 1e-5;
    return fabs(a - b) <= epsilon;
}

// ----------------------------------------------------------------

class LevellerRasterBand;

class LevellerDataset final : public GDALPamDataset
{
    friend class LevellerRasterBand;
    friend class digital_axis;

    int m_version;

    char *m_pszFilename;
    OGRSpatialReference m_oSRS{};

    // char              m_szUnits[8];
    char m_szElevUnits[8];
    double m_dElevScale;  // physical-to-logical scaling.
    double m_dElevBase;   // logical offset.
    GDALGeoTransform m_gt{};
    // double            m_dMeasurePerPixel;
    double m_dLogSpan[2];

    VSILFILE *m_fp;
    vsi_l_offset m_nDataOffset;

    bool load_from_file(VSILFILE *, const char *);

    static bool locate_data(vsi_l_offset &, size_t &, VSILFILE *, const char *);
    static bool get(int &, VSILFILE *, const char *);

    static bool get(size_t &n, VSILFILE *fp, const char *psz)
    {
        return get((int &)n, fp, psz);
    }

    static bool get(double &, VSILFILE *, const char *);
    static bool get(char *, size_t, VSILFILE *, const char *);

    bool write_header();
    bool write_tag(const char *, int);
    bool write_tag(const char *, size_t);
    bool write_tag(const char *, double);
    bool write_tag(const char *, const char *);
    bool write_tag_start(const char *, size_t);
    bool write(int);
    bool write(size_t);
    bool write(double);
    bool write_byte(size_t);

    static const measurement_unit *get_uom(const char *);
    static const measurement_unit *get_uom(UNITLABEL);
    static const measurement_unit *get_uom(double);

    static bool convert_measure(double, double &, const char *pszUnitsFrom);
    bool make_local_coordsys(const char *pszName, const char *pszUnits);
    bool make_local_coordsys(const char *pszName, UNITLABEL);
    const char *code_to_id(UNITLABEL) const;
    UNITLABEL id_to_code(const char *) const;
    UNITLABEL meter_measure_to_code(double) const;
    bool compute_elev_scaling(const OGRSpatialReference &);
    void raw_to_proj(double, double, double &, double &) const;

  public:
    LevellerDataset();
    ~LevellerDataset() override;

    static GDALDataset *Open(GDALOpenInfo *);
    static int Identify(GDALOpenInfo *);
    static GDALDataset *Create(const char *pszFilename, int nXSize, int nYSize,
                               int nBandsIn, GDALDataType eType,
                               char **papszOptions);

    CPLErr GetGeoTransform(GDALGeoTransform &gt) const override;

    CPLErr SetGeoTransform(const GDALGeoTransform &gt) override;

    const OGRSpatialReference *GetSpatialRef() const override;
    CPLErr SetSpatialRef(const OGRSpatialReference *poSRS) override;
};

class digital_axis
{
  public:
    digital_axis() : m_eStyle(LEV_DA_PIXEL_SIZED), m_fixedEnd(0)
    {
        m_d[0] = 0.0;
        m_d[1] = 0.0;
    }

    bool get(LevellerDataset &ds, VSILFILE *fp, int n)
    {
        char szTag[32];
        snprintf(szTag, sizeof(szTag), "coordsys_da%d_style", n);
        if (!ds.get(m_eStyle, fp, szTag))
            return false;
        snprintf(szTag, sizeof(szTag), "coordsys_da%d_fixedend", n);
        if (!ds.get(m_fixedEnd, fp, szTag))
            return false;
        snprintf(szTag, sizeof(szTag), "coordsys_da%d_v0", n);
        if (!ds.get(m_d[0], fp, szTag))
            return false;
        snprintf(szTag, sizeof(szTag), "coordsys_da%d_v1", n);
        if (!ds.get(m_d[1], fp, szTag))
            return false;
        return true;
    }

    double origin(size_t pixels) const
    {
        if (m_fixedEnd == 1)
        {
            switch (m_eStyle)
            {
                case LEV_DA_SIZED:
                    return m_d[1] + m_d[0];

                case LEV_DA_PIXEL_SIZED:
                    return m_d[1] + (m_d[0] * (pixels - 1));
            }
        }
        return m_d[0];
    }

    double scaling(size_t pixels) const
    {
        CPLAssert(pixels > 1);
        if (m_eStyle == LEV_DA_PIXEL_SIZED)
            return m_d[1 - m_fixedEnd];

        return this->length(static_cast<int>(pixels)) / (pixels - 1);
    }

    double length(int pixels) const
    {
        // Return the signed length of the axis.

        switch (m_eStyle)
        {
            case LEV_DA_POSITIONED:
                return m_d[1] - m_d[0];

            case LEV_DA_SIZED:
                return m_d[1 - m_fixedEnd];

            case LEV_DA_PIXEL_SIZED:
                return m_d[1 - m_fixedEnd] * (pixels - 1);
        }
        CPLAssert(false);
        return 0.0;
    }

  protected:
    int m_eStyle;
    int m_fixedEnd;
    double m_d[2];
};

/************************************************************************/
/* ==================================================================== */
/*                            LevellerRasterBand                        */
/* ==================================================================== */
/************************************************************************/

class LevellerRasterBand final : public GDALPamRasterBand
{
    friend class LevellerDataset;

    float *m_pLine;
    bool m_bFirstTime;

  public:
    explicit LevellerRasterBand(LevellerDataset *);
    ~LevellerRasterBand() override;

    bool Init();

    // Geomeasure support.
    const char *GetUnitType() override;
    double GetScale(int *pbSuccess = nullptr) override;
    double GetOffset(int *pbSuccess = nullptr) override;

    CPLErr IReadBlock(int, int, void *) override;
    CPLErr IWriteBlock(int, int, void *) override;
    CPLErr SetUnitType(const char *) override;
};

/************************************************************************/
/*                         LevellerRasterBand()                         */
/************************************************************************/

LevellerRasterBand::LevellerRasterBand(LevellerDataset *poDSIn)
    : m_pLine(nullptr), m_bFirstTime(true)
{
    poDS = poDSIn;
    nBand = 1;

    eDataType = GDT_Float32;

    nBlockXSize = poDS->GetRasterXSize();
    nBlockYSize = 1;  // poDS->GetRasterYSize();
}

/************************************************************************/
/*                           Init()                                     */
/************************************************************************/

bool LevellerRasterBand::Init()
{
    m_pLine = reinterpret_cast<float *>(
        VSI_MALLOC2_VERBOSE(sizeof(float), nBlockXSize));
    return m_pLine != nullptr;
}

LevellerRasterBand::~LevellerRasterBand()
{
    CPLFree(m_pLine);
}

/************************************************************************/
/*                             IWriteBlock()                            */
/************************************************************************/

CPLErr LevellerRasterBand::IWriteBlock(CPL_UNUSED int nBlockXOff,
                                       int nBlockYOff, void *pImage)
{
    CPLAssert(nBlockXOff == 0);
    CPLAssert(pImage != nullptr);
    CPLAssert(m_pLine != nullptr);

    /*  #define sgn(_n) ((_n) < 0 ? -1 : ((_n) > 0 ? 1 : 0) )
        #define sround(_f)                          \
        (int)((_f) + (0.5 * sgn(_f)))
    */
    const size_t pixelsize = sizeof(float);

    LevellerDataset &ds = *cpl::down_cast<LevellerDataset *>(poDS);
    if (m_bFirstTime)
    {
        m_bFirstTime = false;
        if (!ds.write_header())
            return CE_Failure;
        ds.m_nDataOffset = VSIFTellL(ds.m_fp);
    }
    const size_t rowbytes = nBlockXSize * pixelsize;
    const float *pfImage = reinterpret_cast<float *>(pImage);

    if (0 ==
        VSIFSeekL(ds.m_fp, ds.m_nDataOffset + nBlockYOff * rowbytes, SEEK_SET))
    {
        for (size_t x = 0; x < (size_t)nBlockXSize; x++)
        {
            // Convert logical elevations to physical.
            m_pLine[x] = static_cast<float>((pfImage[x] - ds.m_dElevBase) /
                                            ds.m_dElevScale);
        }

#ifdef CPL_MSB
        GDALSwapWords(m_pLine, pixelsize, nBlockXSize, pixelsize);
#endif
        if (1 == VSIFWriteL(m_pLine, rowbytes, 1, ds.m_fp))
            return CE_None;
    }

    return CE_Failure;
}

CPLErr LevellerRasterBand::SetUnitType(const char *psz)
{
    LevellerDataset &ds = *cpl::down_cast<LevellerDataset *>(poDS);

    if (strlen(psz) >= sizeof(ds.m_szElevUnits))
        return CE_Failure;

    strcpy(ds.m_szElevUnits, psz);

    return CE_None;
}

/************************************************************************/
/*                             IReadBlock()                             */
/************************************************************************/

CPLErr LevellerRasterBand::IReadBlock(CPL_UNUSED int nBlockXOff, int nBlockYOff,
                                      void *pImage)

{
    CPLAssert(sizeof(float) == sizeof(GInt32));
    CPLAssert(nBlockXOff == 0);
    CPLAssert(pImage != nullptr);

    LevellerDataset *poGDS = cpl::down_cast<LevellerDataset *>(poDS);

    /* -------------------------------------------------------------------- */
    /*      Seek to scanline.                                               */
    /* -------------------------------------------------------------------- */
    const size_t rowbytes = nBlockXSize * sizeof(float);

    if (0 != VSIFSeekL(poGDS->m_fp,
                       poGDS->m_nDataOffset + nBlockYOff * rowbytes, SEEK_SET))
    {
        CPLError(CE_Failure, CPLE_FileIO, "Leveller seek failed: %s",
                 VSIStrerror(errno));
        return CE_Failure;
    }

    /* -------------------------------------------------------------------- */
    /*      Read the scanline into the image buffer.                        */
    /* -------------------------------------------------------------------- */

    if (VSIFReadL(pImage, rowbytes, 1, poGDS->m_fp) != 1)
    {
        CPLError(CE_Failure, CPLE_FileIO, "Leveller read failed: %s",
                 VSIStrerror(errno));
        return CE_Failure;
    }

/* -------------------------------------------------------------------- */
/*      Swap on MSB platforms.                                          */
/* -------------------------------------------------------------------- */
#ifdef CPL_MSB
    GDALSwapWords(pImage, 4, nRasterXSize, 4);
#endif

    /* -------------------------------------------------------------------- */
    /*      Convert from legacy-format fixed-point if necessary.            */
    /* -------------------------------------------------------------------- */
    float *pf = reinterpret_cast<float *>(pImage);

    if (poGDS->m_version < 6)
    {
        GInt32 *pi = reinterpret_cast<int *>(pImage);
        for (size_t i = 0; i < (size_t)nBlockXSize; i++)
            pf[i] = static_cast<float>(pi[i]) / 65536;
    }

/* -------------------------------------------------------------------- */
/*      Convert raw elevations to realworld elevs.                      */
/* -------------------------------------------------------------------- */
#if 0
    for(size_t i = 0; i < nBlockXSize; i++)
        pf[i] *= poGDS->m_dWorldscale; //this->GetScale();
#endif

    return CE_None;
}

/************************************************************************/
/*                            GetUnitType()                             */
/************************************************************************/
const char *LevellerRasterBand::GetUnitType()
{
    // Return elevation units.

    LevellerDataset *poGDS = cpl::down_cast<LevellerDataset *>(poDS);

    return poGDS->m_szElevUnits;
}

/************************************************************************/
/*                              GetScale()                              */
/************************************************************************/

double LevellerRasterBand::GetScale(int *pbSuccess)
{
    LevellerDataset *poGDS = cpl::down_cast<LevellerDataset *>(poDS);
    if (pbSuccess != nullptr)
        *pbSuccess = TRUE;
    return poGDS->m_dElevScale;
}

/************************************************************************/
/*                             GetOffset()                              */
/************************************************************************/

double LevellerRasterBand::GetOffset(int *pbSuccess)
{
    LevellerDataset *poGDS = cpl::down_cast<LevellerDataset *>(poDS);
    if (pbSuccess != nullptr)
        *pbSuccess = TRUE;
    return poGDS->m_dElevBase;
}

/************************************************************************/
/* ==================================================================== */
/*                              LevellerDataset                         */
/* ==================================================================== */
/************************************************************************/

/************************************************************************/
/*                          LevellerDataset()                           */
/************************************************************************/

LevellerDataset::LevellerDataset()
    : m_version(0), m_pszFilename(nullptr), m_dElevScale(), m_dElevBase(),
      m_fp(nullptr), m_nDataOffset()
{
    m_oSRS.SetAxisMappingStrategy(OAMS_TRADITIONAL_GIS_ORDER);
    memset(m_szElevUnits, 0, sizeof(m_szElevUnits));
    memset(m_dLogSpan, 0, sizeof(m_dLogSpan));
}

/************************************************************************/
/*                          ~LevellerDataset()                          */
/************************************************************************/

LevellerDataset::~LevellerDataset()
{
    FlushCache(true);

    CPLFree(m_pszFilename);

    if (m_fp != nullptr)
        VSIFCloseL(m_fp);
}

static double degrees_to_radians(double d)
{
    return d * (M_PI / 180);
}

static double average(double a, double b)
{
    return 0.5 * (a + b);
}

void LevellerDataset::raw_to_proj(double x, double y, double &xp,
                                  double &yp) const
{
    xp = x * m_gt[1] + m_gt[0];
    yp = y * m_gt[5] + m_gt[3];
}

bool LevellerDataset::compute_elev_scaling(const OGRSpatialReference &sr)
{
    const char *pszGroundUnits = nullptr;

    if (!sr.IsGeographic())
    {
        // For projected or local CS, the elev scale is
        // the average ground scale.
        m_dElevScale = average(m_gt[1], m_gt[5]);

        const double dfLinear = sr.GetLinearUnits();
        const measurement_unit *pu = this->get_uom(dfLinear);
        if (pu == nullptr)
            return false;

        pszGroundUnits = pu->pszID;
    }
    else
    {
        pszGroundUnits = "m";

        const double kdEarthCircumPolar = 40007849;
        const double kdEarthCircumEquat = 40075004;

        const double xr = 0.5 * nRasterXSize;
        const double yr = 0.5 * nRasterYSize;

        double xg[2], yg[2];
        raw_to_proj(xr, yr, xg[0], yg[0]);
        raw_to_proj(xr + 1, yr + 1, xg[1], yg[1]);

        // The earths' circumference shrinks using a sin()
        // curve as we go up in latitude.
        const double dLatCircum =
            kdEarthCircumEquat * sin(degrees_to_radians(90.0 - yg[0]));

        // Derive meter distance between geolongitudes
        // in xg[0] and xg[1].
        const double dx = fabs(xg[1] - xg[0]) / 360.0 * dLatCircum;
        const double dy = fabs(yg[1] - yg[0]) / 360.0 * kdEarthCircumPolar;

        m_dElevScale = average(dx, dy);
    }

    m_dElevBase = m_dLogSpan[0];

    // Convert from ground units to elev units.
    const measurement_unit *puG = this->get_uom(pszGroundUnits);
    const measurement_unit *puE = this->get_uom(m_szElevUnits);

    if (puG == nullptr || puE == nullptr)
        return false;

    const double g_to_e = puG->dScale / puE->dScale;

    m_dElevScale *= g_to_e;
    return true;
}

bool LevellerDataset::write_header()
{
    char szHeader[5];
    strcpy(szHeader, "trrn");
    szHeader[4] = 7;  // TER v7 introduced w/ Lev 2.6.

    if (1 != VSIFWriteL(szHeader, 5, 1, m_fp) ||
        !this->write_tag("hf_w", (size_t)nRasterXSize) ||
        !this->write_tag("hf_b", (size_t)nRasterYSize))
    {
        CPLError(CE_Failure, CPLE_FileIO, "Could not write header");
        return false;
    }

    m_dElevBase = 0.0;
    m_dElevScale = 1.0;

    if (m_oSRS.IsEmpty())
    {
        write_tag("csclass", LEV_COORDSYS_RASTER);
    }
    else
    {
        char *pszWkt = nullptr;
        m_oSRS.exportToWkt(&pszWkt);
        if (pszWkt)
            write_tag("coordsys_wkt", pszWkt);
        CPLFree(pszWkt);
        const UNITLABEL units_elev = this->id_to_code(m_szElevUnits);

        const int bHasECS =
            (units_elev != UNITLABEL_PIXEL && units_elev != UNITLABEL_UNKNOWN);

        write_tag("coordsys_haselevm", bHasECS);

        if (bHasECS)
        {
            if (!this->compute_elev_scaling(m_oSRS))
                return false;

            // Raw-to-real units scaling.
            write_tag("coordsys_em_scale", m_dElevScale);

            // Elev offset, in real units.
            write_tag("coordsys_em_base", m_dElevBase);
            write_tag("coordsys_em_units", units_elev);
        }

        if (m_oSRS.IsLocal())
        {
            write_tag("csclass", LEV_COORDSYS_LOCAL);

            const double dfLinear = m_oSRS.GetLinearUnits();
            const int n = this->meter_measure_to_code(dfLinear);
            write_tag("coordsys_units", n);
        }
        else
        {
            write_tag("csclass", LEV_COORDSYS_GEO);
        }

        if (m_gt[2] != 0.0 || m_gt[4] != 0.0)
        {
            CPLError(CE_Failure, CPLE_IllegalArg,
                     "Cannot handle rotated geotransform");
            return false;
        }

        // todo: GDAL gridpost spacing is based on extent / rastersize
        // instead of extent / (rastersize-1) like Leveller.
        // We need to look into this and adjust accordingly.

        // Write north-south digital axis.
        write_tag("coordsys_da0_style", LEV_DA_PIXEL_SIZED);
        write_tag("coordsys_da0_fixedend", 0);
        write_tag("coordsys_da0_v0", m_gt[3]);
        write_tag("coordsys_da0_v1", m_gt[5]);

        // Write east-west digital axis.
        write_tag("coordsys_da1_style", LEV_DA_PIXEL_SIZED);
        write_tag("coordsys_da1_fixedend", 0);
        write_tag("coordsys_da1_v0", m_gt[0]);
        write_tag("coordsys_da1_v1", m_gt[1]);
    }

    this->write_tag_start("hf_data",
                          sizeof(float) * nRasterXSize * nRasterYSize);

    return true;
}

/************************************************************************/
/*                          SetGeoTransform()                           */
/************************************************************************/

CPLErr LevellerDataset::SetGeoTransform(const GDALGeoTransform &gt)
{
    m_gt = gt;

    return CE_None;
}

/************************************************************************/
/*                           SetSpatialRef()                            */
/************************************************************************/

CPLErr LevellerDataset::SetSpatialRef(const OGRSpatialReference *poSRS)
{
    m_oSRS.Clear();
    if (poSRS)
        m_oSRS = *poSRS;

    return CE_None;
}

/************************************************************************/
/*                           Create()                                   */
/************************************************************************/
GDALDataset *LevellerDataset::Create(const char *pszFilename, int nXSize,
                                     int nYSize, int nBandsIn,
                                     GDALDataType eType, char **papszOptions)
{
    if (nBandsIn != 1)
    {
        CPLError(CE_Failure, CPLE_IllegalArg, "Band count must be 1");
        return nullptr;
    }

    if (eType != GDT_Float32)
    {
        CPLError(CE_Failure, CPLE_IllegalArg, "Pixel type must be Float32");
        return nullptr;
    }

    if (nXSize < 2 || nYSize < 2)
    {
        CPLError(CE_Failure, CPLE_IllegalArg,
                 "One or more raster dimensions too small");
        return nullptr;
    }

    LevellerDataset *poDS = new LevellerDataset;

    poDS->eAccess = GA_Update;

    poDS->m_pszFilename = CPLStrdup(pszFilename);

    poDS->m_fp = VSIFOpenL(pszFilename, "wb+");

    if (poDS->m_fp == nullptr)
    {
        CPLError(CE_Failure, CPLE_OpenFailed,
                 "Attempt to create file `%s' failed.", pszFilename);
        delete poDS;
        return nullptr;
    }

    // Header will be written the first time IWriteBlock
    // is called.

    poDS->nRasterXSize = nXSize;
    poDS->nRasterYSize = nYSize;

    const char *pszValue = CSLFetchNameValue(papszOptions, "MINUSERPIXELVALUE");
    if (pszValue != nullptr)
        poDS->m_dLogSpan[0] = CPLAtof(pszValue);
    else
    {
        delete poDS;
        CPLError(CE_Failure, CPLE_IllegalArg,
                 "MINUSERPIXELVALUE must be specified.");
        return nullptr;
    }

    pszValue = CSLFetchNameValue(papszOptions, "MAXUSERPIXELVALUE");
    if (pszValue != nullptr)
        poDS->m_dLogSpan[1] = CPLAtof(pszValue);

    if (poDS->m_dLogSpan[1] < poDS->m_dLogSpan[0])
    {
        double t = poDS->m_dLogSpan[0];
        poDS->m_dLogSpan[0] = poDS->m_dLogSpan[1];
        poDS->m_dLogSpan[1] = t;
    }

    // --------------------------------------------------------------------
    //      Instance a band.
    // --------------------------------------------------------------------
    LevellerRasterBand *poBand = new LevellerRasterBand(poDS);
    poDS->SetBand(1, poBand);

    if (!poBand->Init())
    {
        delete poDS;
        return nullptr;
    }

    return poDS;
}

bool LevellerDataset::write_byte(size_t n)
{
    unsigned char uch = static_cast<unsigned char>(n);
    return 1 == VSIFWriteL(&uch, 1, 1, m_fp);
}

bool LevellerDataset::write(int n)
{
    CPL_LSBPTR32(&n);
    return 1 == VSIFWriteL(&n, sizeof(n), 1, m_fp);
}

bool LevellerDataset::write(size_t n)
{
    GUInt32 n32 = (GUInt32)n;
    CPL_LSBPTR32(&n32);
    return 1 == VSIFWriteL(&n32, sizeof(n32), 1, m_fp);
}

bool LevellerDataset::write(double d)
{
    CPL_LSBPTR64(&d);
    return 1 == VSIFWriteL(&d, sizeof(d), 1, m_fp);
}

bool LevellerDataset::write_tag_start(const char *pszTag, size_t n)
{
    if (this->write_byte(strlen(pszTag)))
    {
        return (1 == VSIFWriteL(pszTag, strlen(pszTag), 1, m_fp) &&
                this->write(n));
    }

    return false;
}

bool LevellerDataset::write_tag(const char *pszTag, int n)
{
    return (this->write_tag_start(pszTag, sizeof(n)) && this->write(n));
}

bool LevellerDataset::write_tag(const char *pszTag, size_t n)
{
    return (this->write_tag_start(pszTag, sizeof(n)) && this->write(n));
}

bool LevellerDataset::write_tag(const char *pszTag, double d)
{
    return (this->write_tag_start(pszTag, sizeof(d)) && this->write(d));
}

bool LevellerDataset::write_tag(const char *pszTag, const char *psz)
{
    CPLAssert(strlen(pszTag) <= kMaxTagNameLen);

    char sz[kMaxTagNameLen + 1];
    snprintf(sz, sizeof(sz), "%sl", pszTag);
    const size_t len = strlen(psz);

    if (len > 0 && this->write_tag(sz, len))
    {
        snprintf(sz, sizeof(sz), "%sd", pszTag);
        this->write_tag_start(sz, len);
        return 1 == VSIFWriteL(psz, len, 1, m_fp);
    }
    return false;
}

bool LevellerDataset::locate_data(vsi_l_offset &offset, size_t &len,
                                  VSILFILE *fp, const char *pszTag)
{
    // Locate the file offset of the desired tag's data.
    // If it is not available, return false.
    // If the tag is found, leave the filemark at the
    // start of its data.

    if (0 != VSIFSeekL(fp, 5, SEEK_SET))
        return false;

    const int kMaxDescLen = 64;
    for (;;)
    {
        unsigned char c;
        if (1 != VSIFReadL(&c, sizeof(c), 1, fp))
            return false;

        const size_t descriptorLen = c;
        if (descriptorLen == 0 || descriptorLen > (size_t)kMaxDescLen)
            return false;

        char descriptor[kMaxDescLen + 1];
        if (1 != VSIFReadL(descriptor, descriptorLen, 1, fp))
            return false;

        GUInt32 datalen;
        if (1 != VSIFReadL(&datalen, sizeof(datalen), 1, fp))
            return false;

        CPL_LSBPTR32(&datalen);
        descriptor[descriptorLen] = 0;
        if (str_equal(descriptor, pszTag))
        {
            len = (size_t)datalen;
            offset = VSIFTellL(fp);
            return true;
        }
        else
        {
            // Seek to next tag.
            if (0 != VSIFSeekL(fp, (vsi_l_offset)datalen, SEEK_CUR))
                return false;
        }
    }
}

/************************************************************************/
/*                                get()                                 */
/************************************************************************/

bool LevellerDataset::get(int &n, VSILFILE *fp, const char *psz)
{
    vsi_l_offset offset;
    size_t len;

    if (locate_data(offset, len, fp, psz))
    {
        GInt32 value;
        if (1 == VSIFReadL(&value, sizeof(value), 1, fp))
        {
            CPL_LSBPTR32(&value);
            n = static_cast<int>(value);
            return true;
        }
    }
    return false;
}

/************************************************************************/
/*                                get()                                 */
/************************************************************************/

bool LevellerDataset::get(double &d, VSILFILE *fp, const char *pszTag)
{
    vsi_l_offset offset;
    size_t len;

    if (locate_data(offset, len, fp, pszTag))
    {
        if (1 == VSIFReadL(&d, sizeof(d), 1, fp))
        {
            CPL_LSBPTR64(&d);
            return true;
        }
    }
    return false;
}

/************************************************************************/
/*                                get()                                 */
/************************************************************************/
bool LevellerDataset::get(char *pszValue, size_t maxchars, VSILFILE *fp,
                          const char *pszTag)
{
    char szTag[65];

    // We can assume 8-bit encoding, so just go straight
    // to the *_d tag.
    snprintf(szTag, sizeof(szTag), "%sd", pszTag);

    vsi_l_offset offset;
    size_t len;

    if (locate_data(offset, len, fp, szTag))
    {
        if (len > maxchars)
            return false;

        if (1 == VSIFReadL(pszValue, len, 1, fp))
        {
            pszValue[len] = 0;  // terminate C-string
            return true;
        }
    }

    return false;
}

UNITLABEL LevellerDataset::meter_measure_to_code(double dM) const
{
    // Convert a meter conversion factor to its UOM OEM code.
    // If the factor is close to the approximation margin, then
    // require exact equality, otherwise be loose.

    const measurement_unit *pu = this->get_uom(dM);
    return pu != nullptr ? pu->oemCode : UNITLABEL_UNKNOWN;
}

UNITLABEL LevellerDataset::id_to_code(const char *pszUnits) const
{
    // Convert a readable UOM to its OEM code.

    const measurement_unit *pu = this->get_uom(pszUnits);
    return pu != nullptr ? pu->oemCode : UNITLABEL_UNKNOWN;
}

const char *LevellerDataset::code_to_id(UNITLABEL code) const
{
    // Convert a measurement unit's OEM ID to its readable ID.

    const measurement_unit *pu = this->get_uom(code);
    return pu != nullptr ? pu->pszID : nullptr;
}

const measurement_unit *LevellerDataset::get_uom(const char *pszUnits)
{
    for (size_t i = 0; i < CPL_ARRAYSIZE(kUnits); i++)
    {
        if (strcmp(pszUnits, kUnits[i].pszID) == 0)
            return &kUnits[i];
    }
    CPLError(CE_Failure, CPLE_AppDefined, "Unknown measurement units: %s",
             pszUnits);
    return nullptr;
}

const measurement_unit *LevellerDataset::get_uom(UNITLABEL code)
{
    for (size_t i = 0; i < CPL_ARRAYSIZE(kUnits); i++)
    {
        if (kUnits[i].oemCode == code)
            return &kUnits[i];
    }
    CPLError(CE_Failure, CPLE_AppDefined, "Unknown measurement unit code: %08x",
             code);
    return nullptr;
}

const measurement_unit *LevellerDataset::get_uom(double dM)
{
    for (size_t i = kFirstLinearMeasureIdx; i < CPL_ARRAYSIZE(kUnits); i++)
    {
        if (dM >= 1.0e-4)
        {
            if (approx_equal(dM, kUnits[i].dScale))
                return &kUnits[i];
        }
        else if (dM == kUnits[i].dScale)
            return &kUnits[i];
    }
    CPLError(CE_Failure, CPLE_AppDefined,
             "Unknown measurement conversion factor: %f", dM);
    return nullptr;
}

/************************************************************************/
/*                          convert_measure()                           */
/************************************************************************/

bool LevellerDataset::convert_measure(double d, double &dResult,
                                      const char *pszSpace)
{
    // Convert a measure to meters.

    for (size_t i = kFirstLinearMeasureIdx; i < CPL_ARRAYSIZE(kUnits); i++)
    {
        if (str_equal(pszSpace, kUnits[i].pszID))
        {
            dResult = d * kUnits[i].dScale;
            return true;
        }
    }
    CPLError(CE_Failure, CPLE_FileIO, "Unknown linear measurement unit: '%s'",
             pszSpace);
    return false;
}

bool LevellerDataset::make_local_coordsys(const char *pszName,
                                          const char *pszUnits)
{
    m_oSRS.SetLocalCS(pszName);
    double d;
    return (convert_measure(1.0, d, pszUnits) &&
            OGRERR_NONE == m_oSRS.SetLinearUnits(pszUnits, d));
}

bool LevellerDataset::make_local_coordsys(const char *pszName, UNITLABEL code)
{
    const char *pszUnitID = code_to_id(code);
    return pszUnitID != nullptr && make_local_coordsys(pszName, pszUnitID);
}

/************************************************************************/
/*                            load_from_file()                            */
/************************************************************************/

bool LevellerDataset::load_from_file(VSILFILE *file, const char *pszFilename)
{
    // get hf dimensions
    if (!get(nRasterXSize, file, "hf_w"))
    {
        CPLError(CE_Failure, CPLE_OpenFailed,
                 "Cannot determine heightfield width.");
        return false;
    }

    if (!get(nRasterYSize, file, "hf_b"))
    {
        CPLError(CE_Failure, CPLE_OpenFailed,
                 "Cannot determine heightfield breadth.");
        return false;
    }

    if (nRasterXSize < 2 || nRasterYSize < 2)
    {
        CPLError(CE_Failure, CPLE_OpenFailed,
                 "Heightfield raster dimensions too small.");
        return false;
    }

    // Record start of pixel data
    size_t datalen;
    if (!locate_data(m_nDataOffset, datalen, file, "hf_data"))
    {
        CPLError(CE_Failure, CPLE_OpenFailed, "Cannot locate elevation data.");
        return false;
    }

    // Sanity check: do we have enough pixels?
    if (static_cast<GUIntBig>(datalen) !=
        static_cast<GUIntBig>(nRasterXSize) *
            static_cast<GUIntBig>(nRasterYSize) * sizeof(float))
    {
        CPLError(CE_Failure, CPLE_OpenFailed,
                 "File does not have enough data.");
        return false;
    }

    // Defaults for raster coordsys.
    m_gt = GDALGeoTransform();

    m_dElevScale = 1.0;
    m_dElevBase = 0.0;
    strcpy(m_szElevUnits, "");

    if (m_version >= 7)
    {
        // Read coordsys info.
        int csclass = LEV_COORDSYS_RASTER;
        /* (void) */ get(csclass, file, "csclass");

        if (csclass != LEV_COORDSYS_RASTER)
        {
            // Get projection details and units.
            if (csclass == LEV_COORDSYS_LOCAL)
            {
                UNITLABEL unitcode;
                // char szLocalUnits[8];
                int unitcode_int;
                if (!get(unitcode_int, file, "coordsys_units"))
                    unitcode_int = UNITLABEL_M;
                unitcode = static_cast<UNITLABEL>(unitcode_int);

                if (!make_local_coordsys("Leveller", unitcode))
                {
                    CPLError(CE_Failure, CPLE_OpenFailed,
                             "Cannot define local coordinate system.");
                    return false;
                }
            }
            else if (csclass == LEV_COORDSYS_GEO)
            {
                char szWKT[1024];
                if (!get(szWKT, 1023, file, "coordsys_wkt"))
                    return false;

                m_oSRS.importFromWkt(szWKT);
            }
            else
            {
                CPLError(CE_Failure, CPLE_OpenFailed,
                         "Unknown coordinate system type in %s.", pszFilename);
                return false;
            }

            // Get ground extents.
            digital_axis axis_ns, axis_ew;

            if (axis_ns.get(*this, file, 0) && axis_ew.get(*this, file, 1))
            {
                m_gt[0] = axis_ew.origin(nRasterXSize);
                m_gt[1] = axis_ew.scaling(nRasterXSize);
                m_gt[2] = 0.0;

                m_gt[3] = axis_ns.origin(nRasterYSize);
                m_gt[4] = 0.0;
                m_gt[5] = axis_ns.scaling(nRasterYSize);
            }
        }

        // Get vertical (elev) coordsys.
        int bHasVertCS = FALSE;
        if (get(bHasVertCS, file, "coordsys_haselevm") && bHasVertCS)
        {
            get(m_dElevScale, file, "coordsys_em_scale");
            get(m_dElevBase, file, "coordsys_em_base");
            UNITLABEL unitcode;
            int unitcode_int;
            if (get(unitcode_int, file, "coordsys_em_units"))
            {
                unitcode = static_cast<UNITLABEL>(unitcode_int);
                const char *pszUnitID = code_to_id(unitcode);
                if (pszUnitID != nullptr)
                {
                    strncpy(m_szElevUnits, pszUnitID, sizeof(m_szElevUnits));
                    m_szElevUnits[sizeof(m_szElevUnits) - 1] = '\0';
                }
                else
                {
                    CPLError(CE_Failure, CPLE_OpenFailed,
                             "Unknown OEM elevation unit of measure (%d)",
                             unitcode);
                    return false;
                }
            }
            // datum and localcs are currently unused.
        }
    }
    else
    {
        // Legacy files use world units.
        char szWorldUnits[32];
        strcpy(szWorldUnits, "m");

        double dWorldscale = 1.0;

        if (get(dWorldscale, file, "hf_worldspacing"))
        {
            // m_bHasWorldscale = true;
            if (get(szWorldUnits, sizeof(szWorldUnits) - 1, file,
                    "hf_worldspacinglabel"))
            {
                // Drop long name, if present.
                char *p = strchr(szWorldUnits, ' ');
                if (p != nullptr)
                    *p = 0;
            }

#if 0
          // If the units are something besides m/ft/sft,
          // then convert them to meters.

          if(!str_equal("m", szWorldUnits)
             && !str_equal("ft", szWorldUnits)
             && !str_equal("sft", szWorldUnits))
          {
              dWorldscale = this->convert_measure(dWorldscale, szWorldUnits);
              strcpy(szWorldUnits, "m");
          }
#endif

            // Our extents are such that the origin is at the
            // center of the heightfield.
            m_gt[0] = -0.5 * dWorldscale * (nRasterXSize - 1);
            m_gt[3] = -0.5 * dWorldscale * (nRasterYSize - 1);
            m_gt[1] = dWorldscale;
            m_gt[5] = dWorldscale;
        }
        m_dElevScale = dWorldscale;  // this was 1.0 before because
        // we were converting to real elevs ourselves, but
        // some callers may want both the raw pixels and the
        // transform to get real elevs.

        if (!make_local_coordsys("Leveller world space", szWorldUnits))
        {
            CPLError(CE_Failure, CPLE_OpenFailed,
                     "Cannot define local coordinate system.");
            return false;
        }
    }

    return true;
}

/************************************************************************/
/*                          GetSpatialRef()                             */
/************************************************************************/

const OGRSpatialReference *LevellerDataset::GetSpatialRef() const
{
    return m_oSRS.IsEmpty() ? nullptr : &m_oSRS;
}

/************************************************************************/
/*                          GetGeoTransform()                           */
/************************************************************************/

CPLErr LevellerDataset::GetGeoTransform(GDALGeoTransform &gt) const

{
    gt = m_gt;
    return CE_None;
}

/************************************************************************/
/*                              Identify()                              */
/************************************************************************/

int LevellerDataset::Identify(GDALOpenInfo *poOpenInfo)
{
    if (poOpenInfo->nHeaderBytes < 4)
        return FALSE;

    return STARTS_WITH_CI(
        reinterpret_cast<const char *>(poOpenInfo->pabyHeader), "trrn");
}

/************************************************************************/
/*                                Open()                                */
/************************************************************************/

GDALDataset *LevellerDataset::Open(GDALOpenInfo *poOpenInfo)
{
    // The file should have at least 5 header bytes
    // and hf_w, hf_b, and hf_data tags.

    if (poOpenInfo->nHeaderBytes < 5 + 13 + 13 + 16 ||
        poOpenInfo->fpL == nullptr)
        return nullptr;

    if (!LevellerDataset::Identify(poOpenInfo))
        return nullptr;

    const int version = poOpenInfo->pabyHeader[4];
    if (version < 4 || version > 12)
        return nullptr;

    /* -------------------------------------------------------------------- */
    /*      Create a corresponding GDALDataset.                             */
    /* -------------------------------------------------------------------- */

    LevellerDataset *poDS = new LevellerDataset();

    poDS->m_version = version;

    poDS->m_fp = poOpenInfo->fpL;
    poOpenInfo->fpL = nullptr;
    poDS->eAccess = poOpenInfo->eAccess;

    /* -------------------------------------------------------------------- */
    /*      Read the file.                                                  */
    /* -------------------------------------------------------------------- */
    if (!poDS->load_from_file(poDS->m_fp, poOpenInfo->pszFilename))
    {
        delete poDS;
        return nullptr;
    }

    /* -------------------------------------------------------------------- */
    /*      Create band information objects.                                */
    /* -------------------------------------------------------------------- */
    LevellerRasterBand *poBand = new LevellerRasterBand(poDS);
    poDS->SetBand(1, poBand);
    if (!poBand->Init())
    {
        delete poDS;
        return nullptr;
    }

    poDS->SetMetadataItem(GDALMD_AREA_OR_POINT, GDALMD_AOP_POINT);

    /* -------------------------------------------------------------------- */
    /*      Initialize any PAM information.                                 */
    /* -------------------------------------------------------------------- */
    poDS->SetDescription(poOpenInfo->pszFilename);
    poDS->TryLoadXML();

    /* -------------------------------------------------------------------- */
    /*      Check for external overviews.                                   */
    /* -------------------------------------------------------------------- */
    poDS->oOvManager.Initialize(poDS, poOpenInfo->pszFilename,
                                poOpenInfo->GetSiblingFiles());

    return poDS;
}

/************************************************************************/
/*                        GDALRegister_Leveller()                       */
/************************************************************************/

void GDALRegister_Leveller()

{
    if (GDALGetDriverByName("Leveller") != nullptr)
        return;

    GDALDriver *poDriver = new GDALDriver();

    poDriver->SetDescription("Leveller");
    poDriver->SetMetadataItem(GDAL_DCAP_RASTER, "YES");
    poDriver->SetMetadataItem(GDAL_DMD_EXTENSION, "ter");
    poDriver->SetMetadataItem(GDAL_DMD_LONGNAME, "Leveller heightfield");
    poDriver->SetMetadataItem(GDAL_DMD_HELPTOPIC,
                              "drivers/raster/leveller.html");
    poDriver->SetMetadataItem(GDAL_DCAP_VIRTUALIO, "YES");

    poDriver->pfnIdentify = LevellerDataset::Identify;
    poDriver->pfnOpen = LevellerDataset::Open;
    poDriver->pfnCreate = LevellerDataset::Create;

    GetGDALDriverManager()->RegisterDriver(poDriver);
}
