I'm trying to read a GeoTIFF with one band which stores a value between 0 and 3 ( 255 is no maks ). My Goal is to write a little program which takes in a latitude/longitude and returns the fitting pixel value at the geocoordinate in the geotiff.
I downloaded it from here : https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/QQHCIK And if you wanna take a look at it... heres the download link. https://drive.google.com/file/d/104De_YQN1V8tSbj2uhIPO0FfowjnInnX/view?usp=sharing
However, my code does not work. It just outputs the wrong pixel value for a set of geocoordinates every single time. I guess either my geocordinate to pixel transformation is wrong or theres a huge logic mistake.
This was my first try, it prints the wrong value for the geo-coordinate.
Furthermore it crashes with some geocoordinates, a negative longitude makes it crashes because this will make pixelY negative which causes an exception in the raster method.
GdalConfiguration.ConfigureGdal();
var tif = "C:\\Users\\Lars\\Downloads\\pnv_biome.type_biome00k_c_1km_s0..0cm_2000..2017_v0.1.tif";
var lat = 51.0;
var lon = 8.3;
using (var image = Gdal.Open(tif, Access.GA_ReadOnly)) {
var bOneBand = image.GetRasterBand(1);
var width = bOneBand.XSize;
var height = bOneBand.YSize;
// Geocoordinate ( lat, lon ) to pixel in the tiff ?
var geoTransform = new double[6];
image.GetGeoTransform(geoTransform);
Gdal.InvGeoTransform(geoTransform, geoTransform);
var bOne = new int[1];
Gdal.ApplyGeoTransform(geoTransform, lat, lon, out var pixelXF, out var pixelYF);
var pixelX = (int)Math.Floor(pixelXF);
var pixelY = (int)Math.Floor(pixelYF);
// Read pixel
bOneBand.ReadRaster(pixelX, pixelY, 1, 1, bOne, 1, 1,0,0);
Console.WriteLine(bOne[0]); // bOne[0] contains wrong data
}
My second attempt looks like the following... but also outputs the wrong pixel value for the given coordinates.
GdalConfiguration.ConfigureGdal();
var tif = "C:\\Users\\Lars\\Downloads\\pnv_biome.type_biome00k_c_1km_s0..0cm_2000..2017_v0.1.tif";
var lat = 24.7377; // 131.5847
var lon = 131.5847;
using (var image = Gdal.Open(tif, Access.GA_ReadOnly)) {
var bOneBand = image.GetRasterBand(1);
var bOne = new int[1];
// Spatial reference to transform latlng to map coordinates... from python code
var point_srs = new SpatialReference("");
var file_srs = new SpatialReference(image.GetProjection());
point_srs.ImportFromEPSG(4326);
point_srs.SetAxisMappingStrategy(AxisMappingStrategy.OAMS_TRADITIONAL_GIS_ORDER);
var mapCoordinates = new double[2]{ lat, lon};
var transform = new CoordinateTransformation(point_srs, file_srs);
transform.TransformPoint(mapCoordinates);
// Map coordinates to pixel coordinates ?
var geoTransform = new double[6];
image.GetGeoTransform(geoTransform);
Gdal.InvGeoTransform(geoTransform, geoTransform);
Gdal.ApplyGeoTransform(geoTransform, mapCoordinates[0], mapCoordinates[1], out var pixelXF, out var pixelYF);
var pixelX = (int)pixelXF;
var pixelY = (int)pixelYF;
bOneBand.ReadRaster(pixelX, pixelY, 1, 1, bOne, 1, 1, 0,0);
Console.WriteLine(bOne[0]); // bOne[0] contains wrong value
}
Does anyone here have experience on that topic?
I simple cannot fix it after hours of searching and looking at examples.
