How to measure ruggedness by polygon

[Mikhail]

I work with the map of the UK divided into about 5,000 polygons. I'd like to measure the ruggedness of terrain by a polygon with TRI or any other index but can't find the right tool for this task. Could you recommend a solution?

[swfbtucs]

I was glad to see your question as I did not know of TRI and I have a use for it. A little googling found this: https://community.esri.com/t5/water-resources-blog/terrain-ruggedness-index-tri-and-vector-ruggednes...

[Mikhail]

Thank you, I saw this post too. The trouble is I can't find anything like Arc Hydro functions in my system. Can you see them in yours?

[swfbtucs]

No, now that you ask. Interesting. There is nothing referring to hydro in geoprocessing.
Ok, here we go: https://www.esri.com/en-us/industries/water-resources/arc-hydro/downloads#arc-hydro-for-arcgis-pro

[Omar_A]

Hi Mikhail,

To calculate the TRI in ArcGIS, try this workflow:

1. You need a (DEM). Try open-source data websites like the Ordnance Survey, the European Space Agency, and the US Geological Survey. 
2. Convert your polygons into raster format using the Polygon to Raster tool, and choose an appropriate raster cell size that works for your analysis.
3. Extract by Mask tool to clip the DEM raster to the extent of your polygon raster. 
4. Calculate the TRI for each polygon using the Ruggedness Index (TRI) tool in ArcGIS Spatial Analyst extension. Have a look at the tool's documentation.
5. You can then export the TRI values as a table or join them to your original polygon dataset for further analysis.

Other software packages that calculate the TRI include QGIS, GRASS GIS, and SAGA GIS. The specific steps for calculating the TRI may differ slightly between these software packages, but the general workflow should be similar.

Thanks,

[Mikhail]

Hi Omar,

Thank you very much for your advice. Could I use this map as a DEM https://environment.data.gov.uk/image/rest/services/SURVEY/LIDAR_Composite_1m_DSM_2020_Elevation/Ima... ?

Kind regards,

Mikhail

[Omar_A]

Hi Mihhail,

In terms of using a DSM instead of a DEM, it depends on your specific analysis and the data you have available. For example, DSMs include the height of all features on the ground surface, such as buildings and trees, while DEMs represent the bare earth surface. If you are interested in measuring the ruggedness of the bare earth surface, then you should use a DEM. However, a DSM may be more appropriate if you want to include all features on the ground surface in your analysis. Remember that DSMs may produce values higher than DEMs since they include the height of objects on the ground.

In any case, it is essential to understand the data's characteristics and limitations, such as its spatial resolution, accuracy, and vertical datum, before using it for any analysis or modelling.

Thanks,

Omar

[Mikhail]

Hi Omar,

Thank you for your explanation. I found a DEM and followed the workflow you suggested. It all works, except for the last bit: I cannot find a Ruggedness Index tool. I have a Spatial Analyst license, but this tool is nowhere to be seen! Could you advise how you access it?

Kind regards,

Mikhail

[Omar_A]

Hi Mikhail,

I apologize for the inconvenience. Please note that the Topographic Ruggedness Index (TRI) tool is a custom tool exclusively available for our Enterprise users.

However, I have investigated its structure and found that you can calculate TRI using a simple formula in Raster Calculator. I have provided a short video on creating TRI from DEM in ArcMap, which you can access through this link: (194) Topographic Roughness Index (TRI) from DEM / ArcGIS - YouTube

I hope this information is helpful.

Best regards,
Omar

[swfbtucs]

You have to install the tool. See this:

https://www.esri.com/en-us/industries/water-resources/arc-hydro/downloads#arc-hydro-for-arcgis-pro