[GRASS-user] Re: SRTM data aliases in UTM
wollez at gmx.net
Mon Oct 6 13:11:22 EDT 2008
John Stevenson schrieb:
> I have imported some tiles of 1 arcsecond SRTM data into GRASS 6.3 using
> r.in.srtm into a lat-long region. Whenever I import them to a UTM
> region, res=30, I get aliasing problems. This results in a grid of
> lines of jumps in elevation running through my data.
> This happens when I use r.proj. I have also tried generating a text
> file of UTM coordinates via r.stats -1g, and cs2cs. Importing this as a
> raster or vector, and interpolating with r.surf.rst or v.surf.rst also
> give aliasing errors.
> What is the best way round this? Importing at a higher resolution? How
> much higher? My ultimate aim is to compare the SRTM with LiDAR data, so
> if possible I would like to use an exact interpolation where possible.
You have to check what interpolation methods are used. If you don't
specify anything, Grass might use "nearest", but I'm only using Grass
For myself I use gdalwarp with cubic or cubic spline resampling for that
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