| Hi. I am currently using Grass 6.4 on linux and beginning the the process of vectorizing an old NOAA raster map with r.thin. The map is approximately 12,000 pixels by 8,000 pixels wide. According to this post, ( http://osgeo-org.1803224.n2.nabble.com/r-thin-td2718260.html#a2718260 )the iteration variable has to be equal or larger than half the number of cells of the wider line so I increased the iterations to 6,000, and it would up finishing in approximately 4,200 passes. Previously, I was getting excellent preliminary results, with fewer (1,000) iterations, distinct features were visible, however at least 50% of the map was not completed. Now with an increase to 6,000 iterations r.thin completes, but the results are a single 1px wide horizontal line. Im sure I am overlooking something relatively simple; can anyone give me any advice on how to best run r.thin in this particular case? Thanks! Charlie Wetlands |
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Hi,
how do you use r.thin? Can you post the complete command?
Am 09.11.2010 06:25, schrieb charlie:
Hi. I am currently using Grass 6.4 on linux and beginning the the
process of vectorizing an old NOAA raster map with r.thin. The map is
approximately 12,000 pixels by 8,000 pixels wide.According to this post, (
http://osgeo-org.1803224.n2.nabble.com/r-thin-td2718260.html#a2718260
)the iteration variable has to be equal or larger than half the number
of cells of the wider line so I increased the iterations to 6,000, and
it would up finishing in approximately 4,200 passes.Previously, I was getting excellent preliminary results, with fewer
(1,000) iterations, distinct features were visible, however at least 50%
of the map was not completed.Now with an increase to 6,000 iterations r.thin completes, but the
results are a single 1px wide horizontal line. Im sure I am overlooking
something relatively simple; can anyone give me any advice on how to
best run r.thin in this particular case?Thanks!
Charlie
<a href="www.wetlandresearch.com">Wetlands</a>
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charlie wrote:
Hi. I am currently using Grass 6.4 on linux and beginning the the process of vectorizing an old NOAA raster map with r.thin. The map is approximately 12,000 pixels by 8,000 pixels wide.
According to this post, ( http://osgeo-org.1803224.n2.nabble.com/r-thin-td2718260.html#a2718260 )the iteration variable has to be equal or larger than half the number of cells of the wider line so I increased the iterations to 6,000, and it would up finishing in approximately 4,200 passes.
Previously, I was getting excellent preliminary results, with fewer (1,000) iterations, distinct features were visible, however at least 50% of the map was not completed.
Now with an increase to 6,000 iterations r.thin completes, but the results are a single 1px wide horizontal line. Im sure I am overlooking something relatively simple; can anyone give me any advice on how to best run r.thin in this particular case?
What is it you are trying to do? The r.thin module is designed to make line features in a raster exactly one pixel wide so that when converting to a line vector, the line will be clean.
If you run r.thin on a raster that represents areas, and give a high enough iteration value, the areas will eventually be reduced to lines.
Thanks!
Charlie
<a href="www.wetlandresearch.com">Wetlands</a>
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