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## Sample Driver: jdemdataset.cpp

    /******************************************************************************
     * $Id: jdemdataset.cpp.html,v 1.7 2002/12/21 19:13:13 warmerda Exp $
     *
     * Project:  JDEM Reader
     * Purpose:  All code for Japanese DEM Reader
     * Author:   Frank Warmerdam, warmerdam@pobox.com
     *
     ******************************************************************************
     * Copyright (c) 2000, Frank Warmerdam <warmerdam@pobox.com>
     *
     * Permission is hereby granted, free of charge, to any person obtaining a
     * copy of this software and associated documentation files (the "Software"),
     * to deal in the Software without restriction, including without limitation
     * the rights to use, copy, modify, merge, publish, distribute, sublicense,
     * and/or sell copies of the Software, and to permit persons to whom the
     * Software is furnished to do so, subject to the following conditions:
     *
     * The above copyright notice and this permission notice shall be included
     * in all copies or substantial portions of the Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
     * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
     * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     * DEALINGS IN THE SOFTWARE.
     ******************************************************************************
     *
     * $Log: jdemdataset.cpp.html,v $
     * Revision 1.7  2002/12/21 19:13:13  warmerda
     * updated
     *
     * Revision 1.7  2002/09/04 06:50:37  warmerda
     * avoid static driver pointers
     *
     * Revision 1.6  2002/06/12 21:12:25  warmerda
     * update to metadata based driver info
     *
     * Revision 1.5  2001/11/11 23:51:00  warmerda
     * added required class keyword to friend declarations
     *
     * Revision 1.4  2001/07/18 04:51:57  warmerda
     * added CPL_CVSID
     *
     * Revision 1.3  2001/06/21 19:59:51  warmerda
     * added help link
     *
     * Revision 1.2  2000/11/28 02:28:54  warmerda
     * Added error checks, GetGeoTransform and GetProjection
     *
     * Revision 1.1  2000/11/27 19:03:26  warmerda
     * New
     *
     */

    #include "gdal_priv.h"

    CPL_CVSID("$Id: jdemdataset.cpp.html,v 1.7 2002/12/21 19:13:13 warmerda Exp $");

    CPL_C_START
    void    GDALRegister_JDEM(void);
    CPL_C_END

    /************************************************************************/
    /*                            JDEMGetField()                            */
    /************************************************************************/

    static int JDEMGetField( char *pszField, int nWidth )

    {
        char        szWork[32];

        CPLAssert( nWidth < (int) sizeof(szWork) );

        strncpy( szWork, pszField, nWidth );
        szWork[nWidth] = '\0';

        return atoi(szWork);
    }

    /************************************************************************/
    /*                            JDEMGetAngle()                            */
    /************************************************************************/

    static double JDEMGetAngle( char *pszField )

    {
        int         nAngle = JDEMGetField( pszField, 7 );
        int         nDegree, nMin, nSec;

        // Note, this isn't very general purpose, but it would appear
        // from the field widths that angles are never negative.  Nice
        // to be a country in the "first quadrant".

        nDegree = nAngle / 10000;
        nMin = (nAngle / 100) % 100;
        nSec = nAngle % 100;

        return nDegree + nMin / 60.0 + nSec / 3600.0;
    }

    /************************************************************************/
    /* ==================================================================== */
    /*                              JDEMDataset                             */
    /* ==================================================================== */
    /************************************************************************/

    class JDEMRasterBand;

    class JDEMDataset : public GDALDataset
    {
        friend class JDEMRasterBand;

        FILE        *fp;
        GByte       abyHeader[1012];

      public:
                    ~JDEMDataset();

        static GDALDataset *Open( GDALOpenInfo * );

        CPLErr      GetGeoTransform( double * padfTransform );
        const char *GetProjectionRef();
    };

    /************************************************************************/
    /* ==================================================================== */
    /*                            JDEMRasterBand                             */
    /* ==================================================================== */
    /************************************************************************/

    class JDEMRasterBand : public GDALRasterBand
    {
        friend class JDEMDataset;

      public:

                    JDEMRasterBand( JDEMDataset *, int );

        virtual CPLErr IReadBlock( int, int, void * );
    };

    /************************************************************************/
    /*                           JDEMRasterBand()                            */
    /************************************************************************/

    JDEMRasterBand::JDEMRasterBand( JDEMDataset *poDS, int nBand )

    {
        this->poDS = poDS;
        this->nBand = nBand;

        eDataType = GDT_Float32;

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

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

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

    {
        JDEMDataset *poGDS = (JDEMDataset *) poDS;
        char        *pszRecord;
        int         nRecordSize = nBlockXSize*5 + 9 + 2;
        int         i;

        VSIFSeek( poGDS->fp, 1011 + nRecordSize*nBlockYOff, SEEK_SET );

        pszRecord = (char *) CPLMalloc(nRecordSize);
        VSIFRead( pszRecord, 1, nRecordSize, poGDS->fp );

        if( !EQUALN((char *) poGDS->abyHeader,pszRecord,6) )
        {
            CPLFree( pszRecord );

            CPLError( CE_Failure, CPLE_AppDefined,
                      "JDEM Scanline corrupt.  Perhaps file was not transferred\n"
                      "in binary mode?" );
            return CE_Failure;
        }

        if( JDEMGetField( pszRecord + 6, 3 ) != nBlockYOff + 1 )
        {
            CPLFree( pszRecord );

            CPLError( CE_Failure, CPLE_AppDefined,
                      "JDEM scanline out of order, JDEM driver does not\n"
                      "currently support partial datasets." );
            return CE_Failure;
        }

        for( i = 0; i < nBlockXSize; i++ )
            ((float *) pImage)[i] = JDEMGetField( pszRecord + 9 + 5 * i, 5) * 0.1;

        return CE_None;
    }

    /************************************************************************/
    /* ==================================================================== */
    /*                              JDEMDataset                             */
    /* ==================================================================== */
    /************************************************************************/

    /************************************************************************/
    /*                            ~JDEMDataset()                             */
    /************************************************************************/

    JDEMDataset::~JDEMDataset()

    {
        if( fp != NULL )
            VSIFClose( fp );
    }

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

    CPLErr JDEMDataset::GetGeoTransform( double * padfTransform )

    {
        double      dfLLLat, dfLLLong, dfURLat, dfURLong;

        dfLLLat = JDEMGetAngle( (char *) abyHeader + 29 );
        dfLLLong = JDEMGetAngle( (char *) abyHeader + 36 );
        dfURLat = JDEMGetAngle( (char *) abyHeader + 43 );
        dfURLong = JDEMGetAngle( (char *) abyHeader + 50 );

        padfTransform[0] = dfLLLong;
        padfTransform[3] = dfURLat;
        padfTransform[1] = (dfURLong - dfLLLong) / GetRasterXSize();
        padfTransform[2] = 0.0;

        padfTransform[4] = 0.0;
        padfTransform[5] = -1 * (dfURLat - dfLLLat) / GetRasterYSize();

        return CE_None;
    }

    /************************************************************************/
    /*                          GetProjectionRef()                          */
    /************************************************************************/

    const char *JDEMDataset::GetProjectionRef()

    {
        return( "GEOGCS[\"Tokyo\",DATUM[\"Tokyo\",SPHEROID[\"Bessel 1841\",6377397.155,299.1528128,AUTHORITY[\"EPSG\",7004]],TOWGS84[-148,507,685,0,0,0,0],AUTHORITY[\"EPSG\",6301]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",8901]],UNIT[\"DMSH\",0.0174532925199433,AUTHORITY[\"EPSG\",9108]],AXIS[\"Lat\",NORTH],AXIS[\"Long\",EAST],AUTHORITY[\"EPSG\",4301]]" );
    }

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

    GDALDataset *JDEMDataset::Open( GDALOpenInfo * poOpenInfo )

    {
    /* -------------------------------------------------------------------- */
    /*      Before trying JDEMOpen() we first verify that there is at        */
    /*      least one "\n#keyword" type signature in the first chunk of     */
    /*      the file.                                                       */
    /* -------------------------------------------------------------------- */
        if( poOpenInfo->fp == NULL || poOpenInfo->nHeaderBytes < 50 )
            return NULL;

        /* check if century values seem reasonable */
        if( (!EQUALN((char *)poOpenInfo->pabyHeader+11,"19",2)
              && !EQUALN((char *)poOpenInfo->pabyHeader+11,"20",2))
            || (!EQUALN((char *)poOpenInfo->pabyHeader+15,"19",2)
                 && !EQUALN((char *)poOpenInfo->pabyHeader+15,"20",2))
            || (!EQUALN((char *)poOpenInfo->pabyHeader+19,"19",2)
                 && !EQUALN((char *)poOpenInfo->pabyHeader+19,"20",2)) )
        {
            return NULL;
        }

    /* -------------------------------------------------------------------- */
    /*      Create a corresponding GDALDataset.                             */
    /* -------------------------------------------------------------------- */
        JDEMDataset         *poDS;

        poDS = new JDEMDataset();

        poDS->fp = poOpenInfo->fp;
        poOpenInfo->fp = NULL;

    /* -------------------------------------------------------------------- */
    /*      Read the header.                                                */
    /* -------------------------------------------------------------------- */
        VSIFSeek( poDS->fp, 0, SEEK_SET );
        VSIFRead( poDS->abyHeader, 1, 1012, poDS->fp );

        poDS->nRasterXSize = JDEMGetField( (char *) poDS->abyHeader + 23, 3 );
        poDS->nRasterYSize = JDEMGetField( (char *) poDS->abyHeader + 26, 3 );

    /* -------------------------------------------------------------------- */
    /*      Create band information objects.                                */
    /* -------------------------------------------------------------------- */
        poDS->SetBand( 1, new JDEMRasterBand( poDS, 1 ));

        return( poDS );
    }

    /************************************************************************/
    /*                          GDALRegister_JDEM()                          */
    /************************************************************************/

    void GDALRegister_JDEM()

    {
        GDALDriver  *poDriver;

        if( GDALGetDriverByName( "JDEM" ) == NULL )
        {
            poDriver = new GDALDriver();

            poDriver->SetDescription( "JDEM" );
            poDriver->SetMetadataItem( GDAL_DMD_LONGNAME,
                                       "Japanese DEM (.mem)" );
            poDriver->SetMetadataItem( GDAL_DMD_HELPTOPIC,
                                       "frmt_various.html#JDEM" );
            poDriver->SetMetadataItem( GDAL_DMD_EXTENSION, "mem" );

            poDriver->pfnOpen = JDEMDataset::Open;

            GetGDALDriverManager()->RegisterDriver( poDriver );
        }
    }