[GRASS-user] Topo to Raster

[Martin Landa]

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 <markus.metz.giswork at gmail.com>:
> On Tue, Mar 4, 2014 at 7:25 PM, Mark Seibel <mseibel at gmail.com> 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
>>
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-- 
Martin Landa * http://geo.fsv.cvut.cz/gwiki/Landa