[GRASSLIST:7897] Re: Hutchinson's Adaptive Alogrithm for sound DEMs?
dylan at iici.no-ip.org
Sun Aug 14 23:51:34 EDT 2005
Maciek and other GRASS users,
These are great points to consider. My work leads me into the realm of
terrain analysis, so this topic is near and dear to me. I think that it
would be great if the pooled efforts of the GRASS community could be
used to make GRASS the premier DEM creation / modification environment.
Since the quality of a DEM is of the utmost importance when calculating
primary and secondary terrain parameters, documentation of and
confidence in the algorithms used for DEM creation should be a
Currently v.surf.rst provides a very flexible means to produce
elevation surfaces from point and contour data. The recent work by
Tomas Cebecauer and others (See "Processing digital terrain models by
regularized spline with tension: tuning interpolation parameters for
different input datasets" from the proceedings to the 2002 GRASS
conference.) shows how v.surf.rst can be used in a method similar to
ANUDEM to enforce proper drainage networks, by adding a "terrain
In addition, in reference to a recent message from David Finlayson
regarding cross-validation of v.surf.rst derrived data, it might be a
good idea for someone with some experience doing so to make a how-to
document. I for one am still a bit baffled at how to properly use the
cross-validation tools in v.surf.rst.
Of course all of this is easy for me to say, and much harder to
implement. As my C skills are not the best, perhaps I can contribute
to this aspect of future work in the form of documentation...
Any thoughts, ideas from other users?
Soils and Biogeochemistry Graduate Group
University of California at Davis
On Aug 14, 2005, at 12:03 PM, Maciek Sieczka wrote:
> Helena, Markus,
> Since improving v.surf.rst is discussed, I would like to ad a few
> notes from
> a simple user, who doesn't understand all the maths of DEM
> interpolation but
> who would like to obtain decent results. Sorry for any naiveness.
> Please let
> me know what you think and if any of my wishes you find worthy of
> adding to
> From: "Markus Neteler" <neteler at itc.it>
>> Here a FWD from Helena Mitasova:
>> On Tue, Aug 02, 2005 at 07:01:33PM -0400, Helena Mitasova wrote:
>>> We are currently testing different interpolation methods including
>>> topogrid (or whatever its current name is)
> I gues we should call it ANUDEM - after Hutchinson. The TOPOGRID is an
> ArcInfo program, which is an implementation of ANUDEM v. 4.5 or 4.6.3,
> depending ArcInfo/ArcGIS version
>>> and v.surf.rst along with other methods and we
>>> plan to implement modifications/improvements that we find beneficial.
> If I may point 4 features I find very usefull in ANUDEM (and two other
> tools) for creating DEMs from data extracted from topo maps. It would
> great if v.surf.rst could provide them.
> ANUDEM is able to utilize following data besides elevation points and
> 1. watercourses, including their flow direction
> I used it in TOPOGRID. At little effort - only digitise the
> watercourses in
> the direction needed - it is possible to obtain a DEM where the water
> flows exactly the way you want it.
> 2. elevation discontinuity lines, called 'cliffs' in ANUDEM
> This was introduced in version 5.1. I haven't had an occasion to use
> since it is not available in TOPOGRID and I never had the original
> ANUDEM at
> hand. I only read it's supported in new version
> http://cres.anu.edu.au/outputs/anudem.php and think it is a great
> Often elevation contour lines and points alone simply can't express
> all the
> complexity of terrain when gullies, scarps, embakments, walls, other
> breaklines are involved. That's due to these are not parallel to
> isolines, thus cannot be presented as elevation isolines. Trying to
> represent them as points, although in theory doable in *some* cases,
> require a lot of work to digitise points dense enough and to correctly
> estimate each point elevation manually. Yet utilising elevation
> discontinuity lines, digitised from topo maps, could greatly improve
> accuracy - at very little effort. Especially in areas of land slides,
> erosion drived by river or flooding, land deformation due to mining,
> shoreline - to name those I can think of right now.
> Such a functionality is also present in SURGE interpolation software.
> But it's only freeware/shareware for Windows, not free software, is
> limited as to amount of data it can handle in one turn and the input
> format is non standard and pretty complex.
> 3. waterbodies
> I used it in TOPOGRID. The elevation of waterbodies interpolated
> agreed very
> well with their actual elevation as seen on topo maps and they are
> flat like
> they should be. I bet many folks would find it usefull for accurate
> elevation representation in lakelands, visualisation of areas in the
> vicinity of water bodies etc.
> The other feature, not supported in ANUDEM but practical I think, are
> ridges. I found it supported in another DEM interpolation software,
> CatchmentSIM (again freeware for Windows, sigh), as "Interpolation
> Lines". The user can digitise them from topo maps and inlude during
> interpolation to model the mountain ridges in his DEM as he wishes
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