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I have the South America hydro1k data for slopes and I am trying to extract the data using point sampling tool with a grid in Brazil's map. My problem is that, even though vector and raster seem to overlay -- and I have tried many CRS conversions in both the vector and the raster with no success -- when I use the point sampling tool, all the grids get the same value of band from the raster. It seems that the grid map corresponds to just one pixel in the raster. This probably has something to do with the projections, but I haven't been able to solve the problem. Here is the projection data for hydro1k raster

PROJCS["US National Atlas Equal Area",GEOGCS["Unspecified datum based upon the Clarke 1866 Authalic Sphere",DATUM["D_Sphere_Clarke_1866_Authalic",SPHEROID["Clarke_1866_Authalic_Sphere",6370997,0]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["latitude_of_origin",-15],PARAMETER["central_meridian",-60],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1]]

and my Brazil's map is in SIRGAS 2000.

This is what happens when I have the raster in the original projection and Brazil vector in SIRGAS2000.I am posting Brazil's map without the grid just for illustration purposes.

enter image description here And this is what happens when I reproject Brazil vector to the raster projection. enter image description here enter image description here

That is, Brazil vector is much smaller than south america raster.With the sampling tool, all the grid points have the same value for the band. Does anyone has any idea of how to fix this?

whyzar
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Aline Menezes
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  • Are you transforming the projection to SIRGAS2000, or just defining the projection? I don't know the specifics of the tools in QGIS, but I know that this is a very common confusion among ArcMap users (similar question) – Erica Aug 09 '14 at 11:47
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    Hi @Erica, thanks for your comment. Yes, I've seen this question before. I have reprojected SIRGAS2000 to Lambert_Azimuthal_Equal_Area and vice-versa using the tools for reprojection, not for definition. – Aline Menezes Aug 09 '14 at 11:55
  • I'll need to leave it to somebody more familiar with QGIS to answer, then. Sorry I couldn't be of more help! – Erica Aug 09 '14 at 12:16
  • Please specify exactly the steps you are performing to sample the raster - don't leave anything out. – underdark Aug 10 '14 at 11:25

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