Topo to Raster

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Topo to Raster

Martin Landa
Hi all,

is it possible in GRASS to perform something similar to "Topo to
Raster" as known in ArcGIS [1]?

Thanks in advance, Martin

[1] http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z0000007m000000.htm

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Re: Topo to Raster

Mark Seibel
Hi.

 
is it possible in GRASS to perform something similar to "Topo to
Raster" as known in ArcGIS [1]?

[1] http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z0000007m000000.htm


Are there specific inputs of the "topo to raster" tool that are of importance for your application?

Using contour lines as input, I have found the r.surf.nnbathy module to perform very well.  For (LiDAR) point data, my preference is v.surf.rst.  The "topo to raster" tool alters the DEM by filling sinks.  The arcgis approach alters the DEM so that their flow routing tool doesnt stop in every sink.  My preference is to use the data as close to original source as possible, and let the superb GRASS flow and routing algorithms handle routing through the sinks automatically. 

If one wanted to mimic the arcgis method of filling sinks after interpolating, one could run iterations of r.fill.dir to make it depression-less.  This isnt necessary with the hydrologic tools in GRASS because the r.watershed algorithm is intelligent enough to keep seeking the next lowest location the DEM.  Add in the fact that r.watershed has MFD, and GRASS quickly surpasses the ESRI hydrologic toolset offerings.

HTH,
Mark

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Re: Topo to Raster

Markus Metz-3
On Tue, Mar 4, 2014 at 7:25 PM, Mark Seibel <[hidden email]> wrote:

>> Hi.
>
>>
>> is it possible in GRASS to perform something similar to "Topo to
>> Raster" as known in ArcGIS [1]?
>>
>> [1]
>> http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z0000007m000000.htm
>
> Are there specific inputs of the "topo to raster" tool that are of
> importance for your application?
>
> Using contour lines as input, I have found the r.surf.nnbathy module to
> perform very well.

Previously, contour lines created by land surveying provided more
detail than available DEMs. Nowadays (since SRTM of 2001), DEMs
provide more detail than contour lines and contour lines are usually
derived from a DEM. Therefore creating a DEM from contour lines which
if in doubt have been created using a DEM is no longer recommended,
rather use any DEM instead.

> For (LiDAR) point data, my preference is v.surf.rst.
> The "topo to raster" tool alters the DEM by filling sinks.

The ArcGIS reference for sink filling is Goodchild and Mark (1987).
ArcGIS thus ignores the literature of the last 27 years. According to
the ArcGIS documentation, "The program assumes that all unidentified
sinks are errors". Identified sinks are those supplied by the user.
Unfortunately for ArcGIS, unidentified sinks are not errors but
usually true terrain elevation, particularly in the year 1987 when
LIDAR was not yet available and DEMs were derived from radar. That
means that the elevation values surrounding sinks are erroneuos rather
than the sinks themselves. Two (of several) methods to deal with sinks
in a more realistic way are the minimum impact approach of Lindsay &
Creed (2005) which alters the DEM (implemented in GRASS as r.hydrodem)
and r.watershed which does not alter the DEM.

In short, you should not use ArcGIS to perform hydrological analysis
or create a DEM for hydrological analysis because the ESRI tools use
methods from the 1980's. Doing something similar to "Topo to Raster"
as known in ArcGIS does not make sense. Rather use
RiverTools/Whitebox/TauDEM/GRASS.

Markus M


> The arcgis
> approach alters the DEM so that their flow routing tool doesnt stop in every
> sink.  My preference is to use the data as close to original source as
> possible, and let the superb GRASS flow and routing algorithms handle
> routing through the sinks automatically.
>
> If one wanted to mimic the arcgis method of filling sinks after
> interpolating, one could run iterations of r.fill.dir to make it
> depression-less.  This isnt necessary with the hydrologic tools in GRASS
> because the r.watershed algorithm is intelligent enough to keep seeking the
> next lowest location the DEM.  Add in the fact that r.watershed has MFD, and
> GRASS quickly surpasses the ESRI hydrologic toolset offerings.
>
> HTH,
> Mark
>
> _______________________________________________
> grass-user mailing list
> [hidden email]
> http://lists.osgeo.org/mailman/listinfo/grass-user
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Re: Topo to Raster

Mark Seibel
Hi.
 
> Using contour lines as input, I have found the r.surf.nnbathy module to
> perform very well.

Previously, contour lines created by land surveying provided more
detail than available DEMs. Nowadays (since SRTM of 2001), DEMs
provide more detail than contour lines and contour lines are usually
derived from a DEM. Therefore creating a DEM from contour lines which
if in doubt have been created using a DEM is no longer recommended,
rather use any DEM instead.


I certainly agree that contour lines are poor quality input data, however, for situations involving conceptual reclamation, contours are used to build the post-development DEM.  This still allows for (albeit generalized) conceptual modeling of the drainage areas for reclaimed streams and drainage areas, and allows for pre/post development analysis of drainage areas (as it is understood the contours are conceptual, not as-built).   Nice to know that GRASS has modules that can cope with contour data, and still produce adequate and reliable results.


Mark

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Re: Topo to Raster

wenzeslaus
These things are nice to hear, however I was trying to read about that in r.hydrodem manual but it is just confusing in what is similar to what in implementation or results and does not give any overview if you don't know the referenced modules. This reminds me about the request here on the mailing list to create some guidelines or tutorial about which water modules should be used when.

Maybe, some pictures would be helpful. r.slope.aspect has the detailed pictures with numbers, this is nice. Do we have date for in NC sample dataset? What about adding some images to manual during Vienna community sprint? This is the thing which can be done remotely by any GRASS user and than just committed by some developer.

Vaclav

http://grass.osgeo.org/grass70/manuals/addons/r.hydrodem.html


On Tue, Mar 4, 2014 at 3:59 PM, Mark Seibel <[hidden email]> wrote:
Hi.
 
> Using contour lines as input, I have found the r.surf.nnbathy module to
> perform very well.

Previously, contour lines created by land surveying provided more
detail than available DEMs. Nowadays (since SRTM of 2001), DEMs
provide more detail than contour lines and contour lines are usually
derived from a DEM. Therefore creating a DEM from contour lines which
if in doubt have been created using a DEM is no longer recommended,
rather use any DEM instead.


I certainly agree that contour lines are poor quality input data, however, for situations involving conceptual reclamation, contours are used to build the post-development DEM.  This still allows for (albeit generalized) conceptual modeling of the drainage areas for reclaimed streams and drainage areas, and allows for pre/post development analysis of drainage areas (as it is understood the contours are conceptual, not as-built).   Nice to know that GRASS has modules that can cope with contour data, and still produce adequate and reliable results.


Mark

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Re: Topo to Raster

Martin Landa
In reply to this post by Mark Seibel
Hi,

2014-03-04 19:25 GMT+01:00 Mark Seibel <[hidden email]>:

> Are there specific inputs of the "topo to raster" tool that are of
> importance for your application?

not really I just want to show my students that almost everything what
they are doing in the class using ArcGIS they can do using open source
GRASS GIS quite easily  :-)

> Using contour lines as input, I have found the r.surf.nnbathy module to
> perform very well.  For (LiDAR) point data, my preference is v.surf.rst.

Right, `r.surf.nnbathy` is based on Pavel Sakov's nn natural neighbor
interpolation library. This library is provided in MIT licence. Then
we could probably incorporate it into main GRASS source code, right? I
found code in Addons [1], btw, link at [2] doesn't work. The module is
written as a bash script and needs to be ported to Python for G7.

What do you think?

> If one wanted to mimic the arcgis method of filling sinks after
> interpolating, one could run iterations of r.fill.dir to make it
> depression-less.  This isnt necessary with the hydrologic tools in GRASS
> because the r.watershed algorithm is intelligent enough to keep seeking the
> next lowest location the DEM.  Add in the fact that r.watershed has MFD, and
> GRASS quickly surpasses the ESRI hydrologic toolset offerings.

Thanks for clarification.

Martin

[1] http://trac.osgeo.org/grass/browser/grass-addons/grass6/raster/r.surf.nnbathy/r.surf.nnbathy
[2] http://grasswiki.osgeo.org/wiki/AddOns/GRASS_6#r.surf.nnbathy

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Re: Topo to Raster

Martin Landa
In reply to this post by Markus Metz-3
Hi,

the notes bellow would make sense to put on the wiki, where it should go? Martin

2014-03-04 21:34 GMT+01:00 Markus Metz <[hidden email]>:

> On Tue, Mar 4, 2014 at 7:25 PM, Mark Seibel <[hidden email]> wrote:
>>> Hi.
>>
>>>
>>> is it possible in GRASS to perform something similar to "Topo to
>>> Raster" as known in ArcGIS [1]?
>>>
>>> [1]
>>> http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z0000007m000000.htm
>>
>> Are there specific inputs of the "topo to raster" tool that are of
>> importance for your application?
>>
>> Using contour lines as input, I have found the r.surf.nnbathy module to
>> perform very well.
>
> Previously, contour lines created by land surveying provided more
> detail than available DEMs. Nowadays (since SRTM of 2001), DEMs
> provide more detail than contour lines and contour lines are usually
> derived from a DEM. Therefore creating a DEM from contour lines which
> if in doubt have been created using a DEM is no longer recommended,
> rather use any DEM instead.
>
>> For (LiDAR) point data, my preference is v.surf.rst.
>> The "topo to raster" tool alters the DEM by filling sinks.
>
> The ArcGIS reference for sink filling is Goodchild and Mark (1987).
> ArcGIS thus ignores the literature of the last 27 years. According to
> the ArcGIS documentation, "The program assumes that all unidentified
> sinks are errors". Identified sinks are those supplied by the user.
> Unfortunately for ArcGIS, unidentified sinks are not errors but
> usually true terrain elevation, particularly in the year 1987 when
> LIDAR was not yet available and DEMs were derived from radar. That
> means that the elevation values surrounding sinks are erroneuos rather
> than the sinks themselves. Two (of several) methods to deal with sinks
> in a more realistic way are the minimum impact approach of Lindsay &
> Creed (2005) which alters the DEM (implemented in GRASS as r.hydrodem)
> and r.watershed which does not alter the DEM.
>
> In short, you should not use ArcGIS to perform hydrological analysis
> or create a DEM for hydrological analysis because the ESRI tools use
> methods from the 1980's. Doing something similar to "Topo to Raster"
> as known in ArcGIS does not make sense. Rather use
> RiverTools/Whitebox/TauDEM/GRASS.
>
> Markus M
>
>
>> The arcgis
>> approach alters the DEM so that their flow routing tool doesnt stop in every
>> sink.  My preference is to use the data as close to original source as
>> possible, and let the superb GRASS flow and routing algorithms handle
>> routing through the sinks automatically.
>>
>> If one wanted to mimic the arcgis method of filling sinks after
>> interpolating, one could run iterations of r.fill.dir to make it
>> depression-less.  This isnt necessary with the hydrologic tools in GRASS
>> because the r.watershed algorithm is intelligent enough to keep seeking the
>> next lowest location the DEM.  Add in the fact that r.watershed has MFD, and
>> GRASS quickly surpasses the ESRI hydrologic toolset offerings.
>>
>> HTH,
>> Mark
>>
>> _______________________________________________
>> grass-user mailing list
>> [hidden email]
>> http://lists.osgeo.org/mailman/listinfo/grass-user



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Re: Topo to Raster

Martin Landa
In reply to this post by wenzeslaus
Hi,

2014-03-05 2:46 GMT+01:00 Vaclav Petras <[hidden email]>:

> Maybe, some pictures would be helpful. r.slope.aspect has the detailed
> pictures with numbers, this is nice. Do we have date for in NC sample
> dataset? What about adding some images to manual during Vienna community
> sprint? This is the thing which can be done remotely by any GRASS user and
> than just committed by some developer.
>
> Vaclav
>
> http://grass.osgeo.org/grass70/manuals/addons/r.hydrodem.html
> http://grass.osgeo.org/grass70/manuals/r.slope.aspect.html

right, the manual of r.hydrodem should be improved, we can start with
notes which wrote MM to the ML. Any volunteer? Martin
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Re: Topo to Raster

Martin Landa
In reply to this post by Martin Landa
Hi,

2014-04-01 12:37 GMT+02:00 Martin Landa <[hidden email]>:
> Right, `r.surf.nnbathy` is based on Pavel Sakov's nn natural neighbor
> interpolation library. This library is provided in MIT licence. Then
> we could probably incorporate it into main GRASS source code, right? I

ah, nn-c is based on triangle library. But probably it wouldn't be so
difficult to replace this part with GRASS triangulation code or other
libraries like CGAL or so, any opinion? Martin

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Re: Topo to Raster

Maciej Sieczka
In reply to this post by Martin Landa
W dniu 01.04.2014 12:37, Martin Landa pisze:

> found code in Addons [1], btw, link at [2] doesn't work

Corrected that.

> [1] http://trac.osgeo.org/grass/browser/grass-addons/grass6/raster/r.surf.nnbathy/r.surf.nnbathy
> [2] http://grasswiki.osgeo.org/wiki/AddOns/GRASS_6#r.surf.nnbathy

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