Compound Topographic Index/Catchment Wetness Index from DTM data

7635
6
11-30-2011 03:46 AM
KellyWyness
New Contributor
Hi folks,

I know there has been some discussion on the forums about this already but I'm really needing to get some expert advise.

We have DTM data in .asc format for a proposed development site and I need to be able to calculate the CTI/CWI to determine areas of the site are likely to become saturated.  The resolution of the elevation data is 50m so I'm aware that the outputs may not as accurate as required but the development is at the planning stage so we only need to show the general areas.

From previous discussions on the forum it looks like the CTI could be calucated using the Raster Calculator but i've not got much experience using this tool so I would not know where to begin.

If Raster Calculator cannot be used can anyone please direct me to a tool or script that I can download?

We're using ArcGIS 10 with an ArcEditor license.  We also have a license for Spatial Analyst

Many thanks,
Kelly
Tags (2)
0 Kudos
6 Replies
JeffreyEvans
Occasional Contributor III
Kelly,
I have a ArcToolbox in alpha-test that has CTI implemented. The one caveat is that it is written around ArcPy so is only available for ArcGIS 10. If you do not have access to Arc 10 let me know and I can send you an AML, and directions, for calculating CTI in Workstation ArcInfo.

I am not distributing the toolbox on the ESRI site for various reasons including intellectual property rites although, it is free and open source. I am currently writing a program note for publication so there should be a reference at some point. In the interim, please reference the website and attribute authorship to J.S. Evans, J. Oakleaf and S.A. Cushman. This is a work in progress and I am implementing several new tools in the near future, so periodically check the website for changes. Please let me know about any bugs. 

download link for the ArcGIS Geomorphometry and Gradient Metrics Toolbox.
http://conserveonline.org/workspaces/emt/documents/all.html

Here is a link to the licensing attribution.
http://creativecommons.org/licenses/by-nc/3.0/

I would recommend converting your raster into something other than asc. The Imagine (.img) format is a good choice for large rasters. In ArcCatalog you can right click on the data and select "Export > Raster to Different Format" in the context menu.  

Cheers,
Jeff
0 Kudos
EssayasKaba
New Contributor
Hi folks,

I know there has been some discussion on the forums about this already but I'm really needing to get some expert advise.

We have DTM data in .asc format for a proposed development site and I need to be able to calculate the CTI/CWI to determine areas of the site are likely to become saturated.  The resolution of the elevation data is 50m so I'm aware that the outputs may not as accurate as required but the development is at the planning stage so we only need to show the general areas.

From previous discussions on the forum it looks like the CTI could be calucated using the Raster Calculator but i've not got much experience using this tool so I would not know where to begin.

If Raster Calculator cannot be used can anyone please direct me to a tool or script that I can download?

We're using ArcGIS 10 with an ArcEditor license.  We also have a license for Spatial Analyst

Many thanks,
Kelly


Hi;

The simplest way may be to use ILWIS (open ware GIS tool) to generate both. It is a very simple and straight forward procedure. Once you have both you may export them to a TIFF or GRID format and use them in ArcGIS

Essayas
0 Kudos
EnzoViera
New Contributor
Kelly,
I have a ArcToolbox in alpha-test that has CTI implemented. The one caveat is that it is written around ArcPy so is only available for ArcGIS 10. If you do not have access to Arc 10 let me know and I can send you an AML, and directions, for calculating CTI in Workstation ArcInfo.

I am not distributing the toolbox on the ESRI site for various reasons including intellectual property rites although, it is free and open source. I am currently writing a program note for publication so there should be a reference at some point. In the interim, please reference the website and attribute authorship to J.S. Evans, J. Oakleaf and S.A. Cushman. This is a work in progress and I am implementing several new tools in the near future, so periodically check the website for changes. Please let me know about any bugs. 

download link for the ArcGIS Geomorphometry and Gradient Metrics Toolbox.
http://conserveonline.org/workspaces/emt/documents/all.html

Here is a link to the licensing attribution.
http://creativecommons.org/licenses/by-nc/3.0/

I would recommend converting your raster into something other than asc. The Imagine (.img) format is a good choice for large rasters. In ArcCatalog you can right click on the data and select "Export > Raster to Different Format" in the context menu.  

Cheers,
Jeff


Hello, I am using ArcMap 9.2 with Spatial Analyst license, as I can do to use this tool? Actually I want to do the calculations from TWI DEM raster data.
Greetings!

Enzo Viera
enzo@ubuntu.org.uy
0 Kudos
JeffreyEvans
Occasional Contributor III
Please see this thread on calculating CTI using map algebra in raster calculator.

http://forums.arcgis.com/threads/32896-from-DEM-to-CTI?highlight=CTI
0 Kudos
RPatarasuk
New Contributor II
Try SAGA GIS. It is an open source GIS program. I has several topographic indices. However, I don't think can not handle a large scale project.
0 Kudos
ahmedLaamrani
New Contributor
Hi Jeff,
Just to let you know that I successfully installed your Geomorphometry and Gradient Metrics Toolbox - my arcmap (ArcGIS version 10), but is not working. When I launched the Compound Topographic Index function it seems that was running but at the end I couldn�??t get any output raster!  Any idea why this happening? Thanks in advance for your time! 

AL
0 Kudos