topic Re: Pathfinding across a terrain raster in ArcObjects SDK Questions

Pathfinding across a terrain raster

AbelPerez — Mon, 08 Nov 2021 14:05:29 GMT

I am using ArcGIS 10.8 Basic (occasionally Pro but mainly ArcMap).

I am afraid I am not even sure where to start looking but I would appreciate guidance on graph algorithms on a GIS scale. So basically my task is as follows:

1. Within the bounds of the black box I need to find a path from point A to point B.

2. The shaded red polygons are no-go areas so they cannot be traversed.

3. The "optimum" path shall be one of two types:

a. The shortest geodesic distance between the points

b. The path with the lowest terrain traversed w.r.t to the grid raster. In other words, if we were to make a profile of the raster along the path then the path with the lowest max value. Ex: Path A traverses terrain that is at max 120, Path B traverses terrain that is at max 239, Path C traverses terrain that is at max 155, the optimum path in this case would be path A since it traverses the lowest grand max terrain value along its path.

Where would I start looking on how to solve this challenge with ArcGIS? I am quite proficient with ArcObjects and .NET. I'm just afraid I don't even know where to start.

Re: Pathfinding across a terrain raster

GKmieliauskas — Tue, 09 Nov 2021 08:24:08 GMT

Hi,

Have you read this article?

Effects of raster terrain representation on GIS shortest path analysis

You could try to implement author ideas using raster pixel value reading with ArcObjects

Re: Pathfinding across a terrain raster

Anonymous User — Tue, 09 Nov 2021 15:11:19 GMT

Hi Abel

In Pro, you can use DistanceAccumulation and OptimalPathAsLine geoprocessing tools for these types of things.

In ArcMap you can plot true shortest paths around barriers but the newer tools that can use an input cost surface are not available. I recommend that you try to use Pro v2.9 for these types of things.

Here are a couple of introductory blog topics on it:

https://www.esri.com/arcgis-blog/products/spatial-analyst/analytics/distance-analysis-simplified/

https://www.esri.com/arcgis-blog/products/spatial-analyst/analytics/calculating-the-distance-between-locations/

In your specific case you might use your elevation raster as the input 'cost' surface and the red polygon would be your barrier parameter. The output accumulation values won't have any literal meaning because your input cost values aren't true rates but the paths you then plot using OptimalPathAsLine will try to 'stay low'.

regards,

Jim TenBrink

spatial analyst team

Re: Pathfinding across a terrain raster

Anonymous User — Tue, 09 Nov 2021 15:08:18 GMT

This is an excellent article, particularly the 'attribute scale' section. However the article's discussion of purely network based algorithms is no longer applicable to esri's modern distance analysis tools. Esri's 'new' tools (since arcgis pro 2.5) do not experience any meaningful network distance distortion effects. For example, compare CostDistance output to DistanceAccumulation output using a single source and constant cost raster.

This help topic goes into more details. The 'level set' reference at the end of the topic is the basis for the new implementation.

This older blog introduces the network distortion problem, and how to use some of esri's newer tools which avoid that problem, in the limited case of finding shortest 'water distance' paths around coastlines. The links posted as a direct reply to this thread are a more thorough discussion that also includes the other parameters that can be used with the new tools.

regards,

-jt

Re: Pathfinding across a terrain raster

AbelPerez — Tue, 09 Nov 2021 16:46:41 GMT

Thanks folks. I will be spending some time with these links. Thanks for the info.