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I am trying to work with the 1 arc second resolution SRTM DEM from USGS's Earth Explorer, with eventual goals of filling its no data areas with an ASTER grid (also of 1 second resolution). I have an idea of how to complete that step; what I am getting stuck on is the way the SRTM DEM loads in ArcMap. When I open the grid and inspect its properties, it shows that the cells' XY dimensions are 0.00055555556 x 0.00027777778. Meanwhile, with the ASTER grids I have, the cell dimensions are 0.00027777778 x 0.00027777778. I have searched extensively for why the SRTM grid's cell size is rectangular but haven't found much. I have tried downloading the grid in all 3 available formats (BIL, GeoTiff, and DTED) but all open the same way.

Is there a way to find this grid so that it has square cells?

Should I consider using another grid altogether?

Are there workarounds for my rectangular cell issue so that the two DEMs I am using can work together?

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    You just need to resample at the 1/60th degree resolution in both dimensions, to counteract the attempt to handle the fact that meridians get closer together at high latitudes. – Vince Apr 4 '17 at 22:20
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My original explanation made no sense -- not thinking clearly! The SRTM documentation explains: "Please note that tiles above 50° north and below 50° south latitude are sampled at a resolution of 2 arc-second by 1 arc-second."

However, you can still resample your data using the same command I gave:

gdalwarp -tr 0.000277778 -0.000277778 -r cubicspline input.tif output.tif

This interpolates the new pixel values using the method of your choice.

  • Thank you for the response! I hope I can clarify my issue. The properties for both grids indicate that they share the same datum and spatial reference, D_WGS_1984. I tried reprojecting the SRTM grid , but it did not help. I understand that the distances are not equal in the two directions; isn't this always the case (due to convergence of latitudes at the poles)? Anyway the ASTER grid's resolution is also 1 arc second but it is not having the same issue with rectangular cells. – Oscar Lisa Apr 4 '17 at 21:15

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