Dear List,<br><br>I have 30m ASTER DEM from a region (UTM-37) which I am trying to interpolate using ' v.surf.rst ' to obtain 10m resolution DEMs. I prefer this module since I will also need additional maps such as slope, aspect, prof curv, etc. I will try describing my problem below and I will appreciate any suggestions/ideas. Since the original 30m res. image covers a large area, I cropped it into several tiles using 'r.mapcalc'. Each tile has about 12 million cells in 30m res. and 115 million cells in 10m res. and takes an average of 4 hrs to complete one run of v.surf.rst. I sample each tile using 'r.random' at 50%. Then I change the region settings in 'g.region': I align region to resolution and set the resolution to 10m before running <a href="http://v.surf.rs" target="_blank">v.surf.rst</a>. I ran the module at different tension settings (55., 40., 25. and 10.) while keeping smoothing parameter (.1) and other parameters at default settings. When I add legend to my 10m DEM from the toolbar in Map Display, the elevation range is usually a couple meters above or below the original map. After each run, I set my region resolution back to 30m, and using r.mapcalc, I prepare a "difference" map [ (30m DEM) - (10m DEM) ]. In this map, I get extremely high and low values (i.e., the range in the difference map can be -70 to 183 suggesting to me that there is both over- and undershooting), which seem to be limited to mountain tops and some canyons. When I run 'r.report', I can see that actually these "extreme" values are limited to very few cells (about 3-5% of 12 million cells) and the main variation for 95% of cells is within more reasonable range such as +/- 3 meters. I recently became aware of some accuracy issues related to ASTER DEMs especially
in mountainous areas however, I have the same issue for flat parts of this landscape as well. <div><br></div><div>My question is: How can I fix the issue of having these few cells with extreme values?<br><br>I am thinking that:</div>
<div><br>- I may be having this problem because I am trying to interpolate images that are too large (crop tiles of smaller areas?),<br>
<br>- I may be able to fix the negative cells by making them NULL and then using ' r.fill.nulls' module but even if this is advisable, I do not know of a solution for higher than normal value cells.<br> <br>Again, I appreciate your ideas and suggestions. Thank you,<br>
<br clear="all">
<br>-- <br>BÜLENT <br>
<br>
<div style="padding:0px;margin-left:0px;margin-top:0px;overflow:hidden;word-wrap:break-word;color:black;font-size:10px;text-align:left;line-height:130%">
</div>
<div style="padding:0px;margin-left:0px;margin-top:0px;overflow:hidden;word-wrap:break-word;color:black;font-size:10px;text-align:left;line-height:130%">
</div>
</div>