Hi Evan, Thank you for the clearance. I appreciate your helps.
William On Mon, May 9, 2011 at 3:42 PM, Even Rouault <[email protected]> wrote: > Le lundi 09 mai 2011 21:32:39, William Kang a écrit : >> Hi Even, >> After I set it to 0.125, the speed is comparable to the gdalwarp.exe. >> Thanks a lot for your suggestions. >> >> Aside from this topic, I have some questions about the reprojection >> process in gdal. My understanding is that the getGeoTransform returns >> the affine coefficients needed to perform the projection change. If we >> can calculate the four corner points by using the geoTransformer and >> get their coordinates in the new projection coordinate system, we can >> calculate the corresponding bounding box and affine transformation >> coefficients. >> >> But I have read documents and your first reply email suggested that >> some sampling processes along the image edge are necessary to >> calculate the proper bounding box. Why is that? Isn't the four corner >> points enough to determine the new bounding box? Thanks a lot for your >> help. >> > > The 4 corners are not generally sufficient. It is only a rough approximation > if > you don't want to spend more than 20 lines of coding... Sampling along the > image edges is required for accuracy, especially in case of important warping > (for example if you reproject between geographic coordinates <--> polar > projections) > > _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
