Re: [GRASS-user] r.shade.relief: Results Not As Expected
On Tue, Jan 5, 2010 at 2:32 AM, Rich Shepard rshep...@appl-ecosys.com wrote: On Tue, 5 Jan 2010, Glynn Clements wrote: Run r.slope.aspect on the interpolated map, and check for grid-like artifacts. Glynn, Did this. Yes, there is a grid-like appearance to the resulting map. this sounds like a resolution mismatch. If you want to significantly change the resolution of a raster DEM, use - r.resamp.interp - Resamples raster map layers to a finer grid using interpolation. - r.resamp.stats - Resamples raster map layers to a coarser grid using aggregation. How good is the underlying data? If it's noisy, it may need to be filtered before interpolating. How do I check for noisy data? I have all the basic information about the source data and derived maps. Using r.shaded.relief gives a good visual impression. Or create a polar diagram of the aspect map: r.slope.aspect mydem aspect=myaspect d.polar myaspect Also: which version of GRASS are you using? 6.5svn. Markus ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] r.shade.relief: Results Not As Expected
Have you tried a different azimuth? Sometimes certain values can cause features to look inverted for given terrain conditions. Mark On Jan 4, 2010, at 8:32 PM, Rich Shepard rshep...@appl-ecosys.com wrote: On Tue, 5 Jan 2010, Glynn Clements wrote: Run r.slope.aspect on the interpolated map, and check for grid-like artifacts. Glynn, Did this. Yes, there is a grid-like appearance to the resulting map. How good is the underlying data? If it's noisy, it may need to be filtered before interpolating. How do I check for noisy data? I have all the basic information about the source data and derived maps. Also: which version of GRASS are you using? 6.5svn. Thanks, Rich ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] r.shade.relief: Results Not As Expected
Rich Shepard wrote: Run r.slope.aspect on the interpolated map, and check for grid-like artifacts. Glynn, Did this. Yes, there is a grid-like appearance to the resulting map. How good is the underlying data? If it's noisy, it may need to be filtered before interpolating. How do I check for noisy data? I have all the basic information about the source data and derived maps. One trick is to create a filtered map with e.g. r.neighbors method=average or r.mfilter.fp, and subtracting the original map from the resulting map. This will help to highlight any artifacts introduced by processing of the source data. Any such processes should be performed at the map's native resolution, to ensure that artifacts aren't introduced by nearest-neighbour resampling. One thing which can introduce grid-like artifacts is nearest-neighbour resampling (including re-projection) at near-unity scale factors. -- Glynn Clements gl...@gclements.plus.com ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] r.shade.relief: Results Not As Expected
Run r.slope.aspect on the interpolated map, and check for grid-like artifacts. e.g. in the spearfish dataset if you set the slope map's colors with r.colors slope color=bcyr you can see the effect in the elevation.dem map. Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] r.shade.relief: Results Not As Expected
Assuming the 10m resolution of the DEM was too coarse I used g.region to change the resolution to 1m, then ran r.resamp.interp with method=bicubic. This was followe by r.shade.relief. The resulting map looks like a basin-and-range province, with mountains running north-south in parallel. That's not what the basin and surrounding area looks like. I've no idea what I'm doing incorrectly that I cannot produce a proper shaded relief map. I can provide command lines, input DEM and output map if any of this helps. The maps can be provided as screenshots if that works. Rich ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] r.shade.relief: Results Not As Expected
Rich Shepard wrote: Assuming the 10m resolution of the DEM was too coarse I used g.region to change the resolution to 1m, then ran r.resamp.interp with method=bicubic. This was followe by r.shade.relief. The resulting map looks like a basin-and-range province, with mountains running north-south in parallel. That's not what the basin and surrounding area looks like. Run r.slope.aspect on the interpolated map, and check for grid-like artifacts. How good is the underlying data? If it's noisy, it may need to be filtered before interpolating. Also: which version of GRASS are you using? There was a bug in the cubic interpolation code, but that was fixed quite a long time ago. -- Glynn Clements gl...@gclements.plus.com ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] r.shade.relief: Results Not As Expected
On Tue, 5 Jan 2010, Glynn Clements wrote: Run r.slope.aspect on the interpolated map, and check for grid-like artifacts. Glynn, Did this. Yes, there is a grid-like appearance to the resulting map. How good is the underlying data? If it's noisy, it may need to be filtered before interpolating. How do I check for noisy data? I have all the basic information about the source data and derived maps. Also: which version of GRASS are you using? 6.5svn. Thanks, Rich ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
