GDALDEMProcessing : wrong slope processing

[TremblayGIS]

Hello, at first i wish you all a very happy new year.

Here is my issue : when i create slope with the GDALDEMProcessing i got a wrong result. It looks like a binarised file with only 2 values. The strange part is that if i replace "slope" with "aspect" or "hillshade" it works very well.

The result is the same if i change the extension : *.tif, *.dt1 etc...

here is the fonction (so basic...) :

void gdalfile::createSlope() {

GDALDatasetH hDataset; GDALAllRegister(); hDataset = GDALOpen( "D:/datas/n41.dt1", GA_ReadOnly );

GDALDatasetH hOutDS = GDALDEMProcessing("D:/datas/n41_slope.tif", hDataset,"slope",NULL,NULL,NULL);

}

then in the main i call the function like this gdalTest.createSlope();

Do you have any idea ?

Regards

[Even Rouault]

Presumably you need to specify the the -s scale parameter

   Scale is the ratio of vertical units to horizontal
    for Feet:Latlong use scale=370400, for Meters:LatLong use scale=111120 

[TremblayGIS]

Hello, thank you for your return. So instead of NULL i need to set a GDALDEMProcessingOptions, could you give me an example of how using it. I saw i have to deal with GDALDEMProcessingOptionsNew() and GDALDEMProcessingOptionsFree() but i do not know how to do it. it looks that i need to use something like this : GDALDEMProcessingOptions* GDALDEMProcessingOptionsNew (char papszArgv, GDALDEMProcessingOptionsForBinary * psOptionsForBinary ) but i can not see how to deal with that. If you have some example that would be great :)

thanks in advance

[TremblayGIS]

And by the here is what i can get with gdal info :

Projection is `GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4326"]]' Origin = (0.999583,42.000417) Pixel Size = (0.000833,-0.000833)

regards

[Even Rouault]

The API is documented there ​http://gdal.org/gdal__utils_8h.html

More specifically: ​http://gdal.org/gdal__utils_8h.html#ac6e67c9ca37448286a6031e626e551ae

I'm going to close this ticket, as it seems more an issue of using the code that in the code itself. The gdal-dev mailing list or other media are better for questions.

[TremblayGIS]

Hello, i'm trying to step forward with the information you gave to me

here i set the option list, with just the scale option

char papszArgv;

papszArgv = (char)"-s 111120";

....

here is the call GDALDatasetH hOutDS = GDALDEMProcessing("D:/donneesSIG/n41_slope.tif", hDataset,"slope",NULL,GDALDEMProcessingOptionsNew (papszArgv,NULL),NULL); }

i got a 255 error and n41_slope.tif is created. Could you please help me ? regards

[Even Rouault]

The arguments must be separated and the array NULL terminated.

char* papszArgv[] = { "-s", "111120", NULL };

[TremblayGIS]

Thanks it works even if i got a warning : "ISO C++ forbids converting a string constant to 'char*'" regards