[gdal-dev] Working with NED elevation data - part 2
Even Rouault
even.rouault at mines-paris.org
Sun Aug 22 12:43:31 EDT 2010
Stephen,
at first sight, I don't see anything wrong with your code.
You need to include "cpl_conv.h" for CPLMalloc(). And memory allocated with
CPLMalloc() should be freed with CPLFree(). The doc is there :
http://gdal.org/cpl__conv_8h.html (http://gdal.org/ -> API reference
documentation -> Files -> cpl_conv.h )
But that doesn't likely account for the segmentation fault you have. This code
should work just fine with a GTiff or VRT dataset.
Do you use a recent version of GDAL ? If not, retry ;-) If still crashing,
could you attach a debugger and show the stack trace at the place where it
crashes and/or run valgrind on it ?
Best regards,
Even
Le dimanche 22 août 2010 05:23:45, Stephen Woodbridge a écrit :
> OK, well may to answer my own question by reading the GDAL API Tutorial
> and taking a guess at some parts I came up with the following. This is
> basically just a copy of the tutorial and at the end I added some code
> that I'm hoping reads the correct pixel for my lat,lon and prints out
> the elevation.
>
> The tutorial code for "Fetching a Raster Band" works on a GTiff file but
> segv on a VRT file. Not sure why this happened, although there was a
> compiler warning about:
>
> testit.c: In function 'main':
> testit.c:80: warning: cast to pointer from integer of different size
>
> which would be:
>
> float *pafScanline;
> pafScanline = (float *) CPLMalloc(sizeof(float)*nXSize);
>
> I could not find docs on CPLMalloc, or any info on if I need to free
> that and how!
>
> I would appreciate if someone could code review the code at the end and
> comment on whether or not this is correct.
>
> Thanks,
> -Steve
>
> #include <gdal.h>
>
> int main() {
> GDALDatasetH hDataset;
> char *pszFilename = "/u/srcdata/ned2.vrt";
> //char *pszFilename = "/u/srcdata/NED2/-90_28_-84_30.tif";
>
> GDALDriverH hDriver;
> double adfGeoTransform[6];
>
> GDALRasterBandH hBand;
> int nBlockXSize, nBlockYSize;
> int bGotMin, bGotMax;
> double adfMinMax[2];
>
> float *pafScanline;
> int nXSize;
>
> int nXOff, nYOff;
> float elevation;
>
> float lon = -74.0;
> float lat = 42.0;
>
> GDALAllRegister();
>
> hDataset = GDALOpen( pszFilename, GA_ReadOnly );
> if( hDataset == NULL ) {
> printf("Failed to open %s!\n", pszFilename);
> exit(1);
> }
>
> hDriver = GDALGetDatasetDriver( hDataset );
> printf( "Driver: %s/%s\n",
> GDALGetDriverShortName( hDriver ),
> GDALGetDriverLongName( hDriver ) );
>
> printf( "Size is %dx%dx%d\n",
> GDALGetRasterXSize( hDataset ),
> GDALGetRasterYSize( hDataset ),
> GDALGetRasterCount( hDataset ) );
>
> if( GDALGetProjectionRef( hDataset ) != NULL )
> printf( "Projection is `%s'\n", GDALGetProjectionRef( hDataset )
> );
>
> if( GDALGetGeoTransform( hDataset, adfGeoTransform ) == CE_None )
> {
> printf( "Origin = (%.6f,%.6f)\n",
> adfGeoTransform[0], adfGeoTransform[3] );
>
> printf( "Pixel Size = (%.6f,%.6f)\n",
> adfGeoTransform[1], adfGeoTransform[5] );
> }
>
> hBand = GDALGetRasterBand( hDataset, 1 );
> GDALGetBlockSize( hBand, &nBlockXSize, &nBlockYSize );
> printf( "Block=%dx%d Type=%s, ColorInterp=%s\n",
> nBlockXSize, nBlockYSize,
> GDALGetDataTypeName(GDALGetRasterDataType(hBand)),
> GDALGetColorInterpretationName(
> GDALGetRasterColorInterpretation(hBand)) );
>
> adfMinMax[0] = GDALGetRasterMinimum( hBand, &bGotMin );
> adfMinMax[1] = GDALGetRasterMaximum( hBand, &bGotMax );
> if( ! (bGotMin && bGotMax) )
> GDALComputeRasterMinMax( hBand, TRUE, adfMinMax );
>
> printf( "Min=%.3fd, Max=%.3f\n", adfMinMax[0], adfMinMax[1] );
>
> if( GDALGetOverviewCount(hBand) > 0 )
> printf( "Band has %d overviews.\n", GDALGetOverviewCount(hBand));
>
> if( GDALGetRasterColorTable( hBand ) != NULL )
> printf( "Band has a color table with %d entries.\n",
> GDALGetColorEntryCount(
> GDALGetRasterColorTable( hBand ) ) );
>
> /*
> * This section segv trying to do a memset in GDALRasterIO
> * if I use the VRT driver, but works OK on the GTiff file.
> */
> /*
> nXSize = GDALGetRasterBandXSize( hBand );
>
> pafScanline = (float *) CPLMalloc(sizeof(float)*nXSize);
> GDALRasterIO( hBand, GF_Read, 0, 0, nXSize, 1,
> pafScanline, nXSize, 1, GDT_Float32,
> 0, 0 );
> */
>
> /* convert the lon, lat in a pixel location on the file and
> * read that location into a float.
> */
> nXOff = (lon - adfGeoTransform[0]) / adfGeoTransform[1] + 0.5;
> nYOff = (lat - adfGeoTransform[3]) / adfGeoTransform[5] + 0.5;
> GDALRasterIO( hBand, GF_Read, nXOff, nYOff, 1, 1,
> &elevation, 1, 1, GDT_Float32,
> 0, 0 );
> printf("Elevation at %.6f, %.6f = %.1f\n", lon, lat, elevation);
>
> GDALClose(hDataset);
> return(0);
> }
>
> On 8/21/2010 6:07 PM, Stephen Woodbridge wrote:
> > So I have been able to download the NED data and I have US coverage.
> > The data is in GeoTiff and all in a single band Int16 format.
> > I have create a ned.vrt file.
> >
> > So I'm interested in writing a simple program in C that I can pass a
> > lat, lon and get the elevation. I assume I need to open the .vrt file
> > but looking at the GDAL API, I'm not sure how to map the lat, lon to a
> > pixel and then how to fetch the pixel value. If it matter, I will
> > probably extend this later to process a list of locations or maybe
> > extend it to read a shapefile and process the shape through it.
> >
> > Does anyone have a sample program that does something like this.
> >
> > -Steve
> >
> >
> >
> > woodbri at mappy:/u/srcdata$ gdalinfo -stats ned2.vrt
> > Driver: VRT/Virtual Raster
> > Files: ned2.vrt
> > NED2/-100_25_-96_28.tif
> > NED2/-102_28_-96_30.tif
> > NED2/-102_30_-96_32.tif
> > NED2/-102_32_-96_34.tif
> > NED2/-102_34_-96_36.tif
> > NED2/-102_36_-96_38.tif
> > NED2/-102_38_-96_40.tif
> > NED2/-102_40_-96_42.tif
> > NED2/-102_42_-96_44.tif
> > NED2/-102_44_-96_46.tif
> > NED2/-102_46_-96_48.tif
> > NED2/-102_48_-96_50.tif
> > NED2/-108_28_-102_30.tif
> > NED2/-108_30_-102_32.tif
> > NED2/-108_32_-102_34.tif
> > NED2/-108_34_-102_36.tif
> > NED2/-108_36_-102_38.tif
> > NED2/-108_38_-102_40.tif
> > NED2/-108_40_-102_42.tif
> > NED2/-108_42_-102_44.tif
> > NED2/-108_44_-102_46.tif
> > NED2/-108_46_-102_48.tif
> > NED2/-108_48_-102_50.tif
> > NED2/-114_30_-108_32.tif
> > NED2/-114_32_-108_34.tif
> > NED2/-114_34_-108_36.tif
> > NED2/-114_36_-108_38.tif
> > NED2/-114_38_-108_40.tif
> > NED2/-114_40_-108_42.tif
> > NED2/-114_42_-108_44.tif
> > NED2/-114_44_-108_46.tif
> > NED2/-114_46_-108_48.tif
> > NED2/-114_48_-108_50.tif
> > NED2/-120_32_-114_34.tif
> > NED2/-120_34_-114_36.tif
> > NED2/-120_36_-114_38.tif
> > NED2/-120_38_-114_40.tif
> > NED2/-120_40_-114_42.tif
> > NED2/-120_42_-114_44.tif
> > NED2/-120_44_-114_46.tif
> > NED2/-120_46_-114_48.tif
> > NED2/-120_48_-114_50.tif
> > NED2/-123_33_-120_37.tif
> > NED2/-125_37_-120_39.tif
> > NED2/-125_39_-120_42.tif
> > NED2/-126_42_-120_44.tif
> > NED2/-126_44_-120_46.tif
> > NED2/-126_46_-120_48.tif
> > NED2/-126_48_-120_50.tif
> > NED2/133_6.5_138.5_10.tif
> > NED2/-139.0019842_51.9997277_-127.0018384_58.9998127.tif
> > NED2/-139.0024054_58.9997472_-127.0018101_66.0000944.tif
> > NED2/144_13_146_16.tif
> > NED2/151_5_163.5_8.tif
> > NED2/-157_18_-152_23.tif
> > NED2/-157.5_18.75_-154.5_21.5.tif
> > NED2/-160.5_21_-157.5_22.5.tif
> > NED2/-162_18_-157_23.tif
> > NED2/-171_-14.5_-169_-14.tif
> > NED2/-68_17_-64_18.tif
> > NED2/-72.0002778_40.9999994_-67.9999992_44.tif
> > NED2/-72.0002778_44_-66_46.tif
> > NED2/-72.0002778_46_-66_48.tif
> > NED2/-78.0002778_33.0000047_-75.0000047_36.tif
> > NED2/-78.0002778_36_-72_38.tif
> > NED2/-78.0002778_38_-72_40.tif
> > NED2/-78.0002778_40_-72_42.tif
> > NED2/-78.0002778_42_-72_44.tif
> > NED2/-78.0002778_44_-72_46.tif
> > NED2/-84.0002778_24_-78_26.tif
> > NED2/-84.0002778_26_-78_28.tif
> > NED2/-84.0002778_28_-78_30.tif
> > NED2/-84.0002778_30_-78_32.tif
> > NED2/-84.0002778_32_-78_34.tif
> > NED2/-84.0002778_34_-78_36.tif
> > NED2/-84.0002778_36_-78_38.tif
> > NED2/-84.0002778_38_-78_40.tif
> > NED2/-84.0002778_40_-78_42.tif
> > NED2/-84.0002778_42_-78_44.tif
> > NED2/-85.0002778_44.0000047_-82.0000047_47.tif
> > NED2/-90_28_-84_30.tif
> > NED2/-90_30_-84_32.tif
> > NED2/-90_32_-84_34.tif
> > NED2/-90_34_-84_36.tif
> > NED2/-90_36_-84_38.tif
> > NED2/-90_38_-84_40.tif
> > NED2/-90_40_-84_42.tif
> > NED2/-90_42_-84_44.tif
> > NED2/-90_44_-85_46.tif
> > NED2/-90_46_-85_49.tif
> > NED2/-96_28_-90_30.tif
> > NED2/-96_30_-90_32.tif
> > NED2/-96_32_-90_34.tif
> > NED2/-96_34_-90_36.tif
> > NED2/-96_36_-90_38.tif
> > NED2/-96_38_-90_40.tif
> > NED2/-96_40_-90_42.tif
> > NED2/-96_42_-90_44.tif
> > NED2/-96_44_-90_46.tif
> > NED2/-96_46_-90_48.tif
> > NED2/-96_48_-90_50.tif
> > Size is 1180816, 284173
> > Coordinate System is:
> > GEOGCS["WGS 84",
> > DATUM["WGS_1984",
> > SPHEROID["WGS 84",6378137,298.257223563,
> > AUTHORITY["EPSG","7030"]],
> > AUTHORITY["EPSG","6326"]],
> > PRIMEM["Greenwich",0],
> > UNIT["degree",0.0174532925199433],
> > AUTHORITY["EPSG","4326"]]
> > Origin = (-171.000000000113090,66.000094447240443)
> > Pixel Size = (0.000283278659440,-0.000283278659440)
> > Corner Coordinates:
> > Upper Left (-171.0000000, 66.0000944) (171d 0'0.00"W, 66d 0'0.34"N)
> > Lower Left (-171.0000000, -14.5000520) (171d 0'0.00"W, 14d30'0.19"S)
> > Upper Right ( 163.4999735, 66.0000944) (163d29'59.90"E, 66d 0'0.34"N)
> > Lower Right ( 163.4999735, -14.5000520) (163d29'59.90"E, 14d30'0.19"S)
> > Center ( -3.7500132, 25.7500212) ( 3d45'0.05"W, 25d45'0.08"N)
> > Band 1 Block=128x128 Type=Int16, ColorInterp=Gray
> > Minimum=-83.000, Maximum=4665.000, Mean=25.333, StdDev=189.129
> > Metadata:
> > STATISTICS_MINIMUM=-83
> > STATISTICS_MAXIMUM=4665
> > STATISTICS_MEAN=25.332848474484
> > STATISTICS_STDDEV=189.12886049417
> > _______________________________________________
> > gdal-dev mailing list
> > gdal-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
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