Hi List, This is my first post here so please let me know if my question would be better placed elsewhere. I am struggling with re-projecting integer grids using gdalwarp and would appreciate some help.
I have two grids containing land use data at different scales: grid 1) a 50m (esri binary) grid in albers, grid 2) a 1km (ascii) grid in geographics. I would like to project these to a common coordinate system with resolution corresponding to grid 1 so I can perform cross tabulations and alike. I have tried going in both directions The calls I have tried are: call 1) re-project and re-sample grid 2 to the same projection as grid 1. I have obtained the parameters from the property pages of grid 1 in QGIS: gdalwarp ^ -t_srs "+proj=aea +lat_1=-18 +lat_2=-36 +lat_0=0 +lon_0=132 +x_0=0 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs" ^ -te -1888000 -4847000 2122000 -1010000 ^ -tr 50 -50 ^ -dstnodata -32768 ^ nlum.asc nlum_warped.tif call 2) re-project grid 1 to have the same projection as grid 2. Here I have not specified the resolution and was planning to also re-sample grid 2 to the resolution of the result. I get the parameters from the QGIS property pages of grid 2: gdalwarp ^ -t_srs "+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs" ^ -te 112.505 -44.0055 154.005 -9.995 ^ -dstnodata -32768 ^ clumfill clum_warped.tif In the first call I get 24Gb of complete rubbish. When I open the result in QGIS noting is shown (visually) and the cell values contain what appears to be uninitialised junk. In the second call, I get a grid that looks similar to what I want, but the cell value ranges are different ([100, 663] in the input and [0, 663] in the result) and the histograms are different. I thought that by (implicitly) choosing nearest neighbour the values in the output must be a subset of those in the input. Can anyone suggest what might be going wrong? Thanks in advance, Simon Knapp _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
