WolfgangZ wrote:
John Stevenson schrieb:
Hi,
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.
Cheers
John
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
rarely.
For myself I use gdalwarp with cubic or cubic spline resampling for
that task.
http://gdal.org/gdalwarp.html
Regards
Wolfgang
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Hi Wolfgang,
Thanks for the suggestion. I just tried with GDAL_warp and got the same
problem. I tried linear, cubic and cubic spline interpolation. The 30m
grid spacing is very close to the 00:00:01 resolution of the data. My
final map ends up with a kind of grid pattern superimposed that is most
visible on steeper slopes. I am using tiles n33w117 and n34w117 and
projecting to UTM (epsg:26911).
Does anyone else have suggestions on how to convert it to UTM without
this aliasing issue?
Thanks
John
--
Dr John Stevenson
Postdoctoral Research Associate
School of Earth, Atmospheric and Environmental Sciences
Williamson Building (Room 2.42)
University of Manchester
Manchester M13 9PL, UK
tel. +44(0)161 306 6585; fax. +44(0)161 306 9361;
[EMAIL PROTECTED]
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