I have 2006 land cover GeoTiff from the USGS site (for a county in VA, USA). The projection is Albers Conical Equal Area Units. The download came with an HTML metadata file that tells me the geo extent in terms of E/W and N/S bounds. If it matters, I created the dataset using the USGS download tool by selecting a particular county.
I am using GDAL to access the data.
If I take the raster sizes and convert the four corners to WGS84 geo coordinates, I get different geo values for the same pixel value. In other words, if the x pixel coordinate is 0, then I get a different latitude depending upon whether y is 0 or 4194 (the raster height). Is this because the rectangular raster image is mapped into a trapezoid on the sphere?
If I take the geo extents from the metadata file and iterate over them, stepping by 1% of the range, converting each geo point to a pixel and line index, I get lots of invalid (negative or too large) index values. Why would this be?