[GRASS-user] v.surf.rst vs r.slope.aspect

GRASS GRASS user
1

Dear list,

For a project, I need to derive parameters like slope and aspect from
a high-res DEM from a LiDAR point cloud.

There are several way to do this in GRASS:

- v.surf.rst
- r.slope.aspect
- r.param.scale is a bit special and, I think, has a different purpose.

How do RST and r.slope.aspect compare? I can see (using difference
maps or the profile tool) the results are different, but I'm not too
sure which one to use at the end of the day.

Any thoughts/references on that?

Cheers,

Pierre

--
Scientist
Landcare Research, New Zealand

2

On 07/06/11 07:23, Pierre Roudier wrote:

Dear list,

For a project, I need to derive parameters like slope and aspect from
a high-res DEM from a LiDAR point cloud.

There are several way to do this in GRASS:

- v.surf.rst
- r.slope.aspect
- r.param.scale is a bit special and, I think, has a different purpose.

How do RST and r.slope.aspect compare? I can see (using difference
maps or the profile tool) the results are different, but I'm not too
sure which one to use at the end of the day.

v.surf.rst estimates a surface from points and then gives you the slope and aspect resulting directly from the approximation function. r.slope.aspect uses an existing DEM and calculates slope and aspects within a 3x3 neighbourhood.

When you say that there are differences, which DEM did you use with r.slope.aspect ? The one create by the v.surf.rst run ?

Moritz

3

Hi Moritz,

When you say that there are differences, which DEM did you use with
r.slope.aspect ? The one create by the v.surf.rst run ?

Yes - for the sake of the test, I generated a DEM and slope using
v.surf.rst. Then I used r.slope.aspect on that DEM, and compared its
output with the v.surf.rst one. Indeed, the r.slope.aspect looks like
a smoother version of v.surf.rst. Sort of between the v.surf.rst
result and its 3x3 average smooting (using r.neighbors).

v.surf.rst estimates a surface from points and then gives you the slope and
aspect resulting directly from the approximation function. r.slope.aspect
uses an existing DEM and calculates slope and aspects within a 3x3
neighbourhood.

Okay, so v.surf.rst gives a sharper result? I was wondering if it was
the case... or if it was more "noisy".

Cheers,

Pierre

--
Scientist
Landcare Research, New Zealand

4

Dear GRASS users,

I have been working on automating a technique known as Local Relief Modelling (see http://www.ag-caa.de/caanlde/paperdownload/hesse.pdf). The process allows the extraction of microtopographic changes from a DEM (in this case archaeological remains) and is very useful in areas of large topographic variation e.g mountain ranges where small scale features are masked by large shadows in shaded relief models.

I have written and extensively tested a bash script in GRASS 6.4 as part of my doctoral work and would like to make it publicly available so that other researchers can access and use this tool. To do this I need a mentor, so I was wondering if anyone could spare a few hours to help me?

I look forward to hearing from you,

Best wishes,

Rebecca Bennett

Postgraduate Researcher (Archaeology Group)
School of Applied Sciences, Bournemouth University

5

Hi Andras,

Thanks for responding so quickly! I have read the information here http://trac.osgeo.org/grass/wiki/HowToContribute but I’m not exactly certain what the mentor needs to do. I think they need previous experience of the GRASS-svn, code and uploading to the wiki? I have not contributed before so will need someone to help guide me through the process.

I don’t know if the mentor is required to check / run the code as well. I regularly use it for my work and have recently distributed it to a few of my colleagues to test with good results. However, a GRASS expert opinion of it would be most useful!

I should also mention that I have only run the script on linux (Ubuntu 64 bit) so some advice on developing a windows compatible version would be helpful as most of my contemporaries use GRASS on windows.

Please let me know if you are interested and I will send through the script and readme notes for you to look at.

Best wishes,
Rebecca

From: Bödőcs András bodocs.andras@btk.elte.hu
To: Rebecca Bennett rabennett@ymail.com
Sent: Tue, 7 June, 2011 11:01:37
Subject: Re: [GRASS-user] mentor required to help publish a GRASS addon (DEM)

Dear Rebecca,

What do you need exactly?
The stuff is very interesting.

bw
András

011.06.07. 11:02:29 dátumon Rebecca Bennett rabennett@ymail.com írta:

Dear GRASS users,

I have been working on automating a technique known as Local Relief Modelling (see http://www.ag-caa.de/caanlde/paperdownload/hesse.pdf). The process allows the extraction of microtopographic changes from a DEM (in this case archaeological remains) and is very useful in areas of large topographic variation e.g mountain ranges where small scale features are masked by large shadows in shaded relief models.

I have written and extensively tested a bash script in GRASS 6.4 as part of my doctoral work and would like to make it publicly available so that other researchers can access and use this tool. To do this I need a mentor, so I was wondering if anyone could spare a few hours to help me?

I look forward to hearing from you,

Best wishes,

Rebecca Bennett

Postgraduate Researcher (Archaeology Group)
School of Applied Sciences, Bournemouth University

–

Bödőcs András, PhD
ELTE Régészettudományi Intézet
Térinformatika Labor

Budapest, H-1088
Múzeum krt. 4/b.
T: +36-1-4116554, +36-1-4855200/2910
F: +36-1-4116553
E-mail: bodocs.andras@btk.elte.hu
www: http://regeszet.elte.hu

6

Pierre,

-r.param.scale is more appropriate for high resolution elevation data than other modules. It permits to select the kernel (window size) for the estimation of parameters. Land surface parameters depend on DEM resolution and size of computation window. High elevation data are susceptible to noise and it is better to use a kernel larger than 3 when calculating slope and other parameters.

For references check module help and the following: Wood, J.D. (1996) The geomorphological characterisation of digital elevation models PhD Thesis, University of Leicester, UK,http://www.soi.city.ac.uk/~jwo/phd; Hengl, T. and I. S. Evans (2009). Mathematical and Digital Models of the Land Surface. Geomorphometry- Concepts, Software, Applications. T. H. a. H. I. Reuter, Elsevier. Volume 33: 31-63; and Reuter, H. I., T. Hengl, et al. (2009). Preparation of DEMs for Geomorphometric Analysis. Geomorphometry- Concepts, Software, Applications. T. H. a. H. I. Reuter, Elsevier. Volume 33: 87-120.

Edgar Pimiento
e_pimiento@yahoo.com
Public Works Division, Shimane Prefecture, Japan

________________________________
From: Pierre Roudier <pierre.roudier@gmail.com>
To: GRASS <grass-user@lists.osgeo.org>
Sent: Tuesday, June 7, 2011 2:23 PM
Subject: [GRASS-user] v.surf.rst vs r.slope.aspect

Dear list,

For a project, I need to derive parameters like slope and aspect from
a high-res DEM from a LiDAR point cloud.

There are several way to do this in GRASS:

- v.surf.rst
- r.slope.aspect
- r.param.scale is a bit special and, I think, has a different purpose.

How do RST and r.slope.aspect compare? I can see (using difference
maps or the profile tool) the results are different, but I'm not too
sure which one to use at the end of the day.

Any thoughts/references on that?

Cheers,

Pierre

--
Scientist
Landcare Research, New Zealand
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

7

Dear Rebecca,

I have recently worked on a number of GRASS shell scripts
for signal processing (also with archaeological applications
in mind). Email me your script and note, or (provided it's
not very large), attach and email it to this list.

I will have a look at it to see if it needs any improvements
and test it on Windows and Mac OS X (not this week, though).

Have you written a manual page for it yet?

Cheers,

Ben

----- Original Message -----

Dear GRASS users,

I have been working on automating a technique known as Local Relief
Modelling (see http://www.ag-caa.de/caanlde/paperdownload/hesse.pdf ).
The process allows the extraction of microtopographic changes from a
DEM (in this case archaeological remains) and is very useful in areas
of large topographic variation e.g mountain ranges where small scale
features are masked by large shadows in shaded relief models.

I have written and extensively tested a bash script in GRASS 6.4 as
part of my doctoral work and would like to make it publicly available
so that other researchers can access and use this tool. To do this I
need a mentor, so I was wondering if anyone could spare a few hours to
help me?

I look forward to hearing from you,

Best wishes,

Rebecca Bennett

Postgraduate Researcher (Archaeology Group)
School of Applied Sciences, Bournemouth University

_______________________________________________ grass-user mailing
list grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

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8

Thanks Edgar, the results are indeed better with a bit of smoothing.

Cheers,

Pierre

2011/6/7 Edgar Pimiento <e_pimiento@yahoo.com>:

Pierre,

-r.param.scale is more appropriate for high resolution elevation data than other modules. It permits to select the kernel (window size) for the estimation of parameters. Land surface parameters depend on DEM resolution and size of computation window. High elevation data are susceptible to noise and it is better to use a kernel larger than 3 when calculating slope and other parameters.

For references check module help and the following: Wood, J.D. (1996) The geomorphological characterisation of digital elevation models PhD Thesis, University of Leicester, UK,http://www.soi.city.ac.uk/~jwo/phd; Hengl, T. and I. S. Evans (2009). Mathematical and Digital Models of the Land Surface. Geomorphometry- Concepts, Software, Applications. T. H. a. H. I. Reuter, Elsevier. Volume 33: 31-63; and Reuter, H. I., T. Hengl, et al. (2009). Preparation of DEMs for Geomorphometric Analysis. Geomorphometry- Concepts, Software, Applications. T. H. a. H. I. Reuter, Elsevier. Volume 33: 87-120.

Edgar Pimiento
e_pimiento@yahoo.com
Public Works Division, Shimane Prefecture, Japan

________________________________
From: Pierre Roudier <pierre.roudier@gmail.com>
To: GRASS <grass-user@lists.osgeo.org>
Sent: Tuesday, June 7, 2011 2:23 PM
Subject: [GRASS-user] v.surf.rst vs r.slope.aspect

Dear list,

For a project, I need to derive parameters like slope and aspect from
a high-res DEM from a LiDAR point cloud.

There are several way to do this in GRASS:

- v.surf.rst
- r.slope.aspect
- r.param.scale is a bit special and, I think, has a different purpose.

How do RST and r.slope.aspect compare? I can see (using difference
maps or the profile tool) the results are different, but I'm not too
sure which one to use at the end of the day.

Any thoughts/references on that?

Cheers,

Pierre

--
Scientist
Landcare Research, New Zealand
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

--
Scientist
Landcare Research, New Zealand