Create Random Points tool generating points within minimum allowed distance

[FDavisIV]

Hello, I am attempting to use the Create Random Points tool in ArcGIS Pro 3.0.0, but am having issues with the minimum allowed distance. I am attempting to create 40 points spaced 5 km apart along a river network, which is composed of many small segments (like a branched structure) that I have dissolved together. The attribute table for the dissolved river network feature contains only one entry.

So, the "constraining feature class" is the dissolved river network, the "number of points" is 40 (value, not field), and the "minimum allowed distance" is 5 kilometers (linear unit, not field). Beyond that, everything is left at a default. When I run the tool, unfortunately it does not respect the minimum allowed distance, neither in terms of river-distance or absolute-distance. I have run the tool many times, but it still places points directly next to each other on occasion.

I am aware of the below information found on the ESRI help page for the Create Random Points tool, found here:

"Random points may be within the minimum allowed distance if they were generated inside or along different constraining feature parts."

I suspect that the tool is still considering each segment of the river network as a separate feature parts, even though I have dissolved them. This is because if I go back and reference the original network, it doesn't place more than one point per line feature, and nearby points occur close to the transition of one segment to another.

Example attached below, displaying two points created using the tool. The points were generated using the dissolved river network, NOT the original river network. The original river network is displayed for reference, one segment selected. Despite the minimum allowed distance specified at 5 km, the points are less than 500 m apart.

Interestingly, if I specify an absurdly large minimum allowed distance, such as 10,000 kilometers, it only generates 1 point. If the explanation above were correct, wouldn't it generate one point per segment?

I have tried using a narrow buffer of the river network instead of the river network itself, but this yielded the same result. I have also ensured that the tool is using the correct coordinate system, and I have tried restarting the application, to no avail. 

Any insight into how I can make the minimum allowed distance function properly would be greatly appreciated. Alternatively, if there is a way to force ArcGIS to "forget" the original boundaries of the river segments, that may also work. Suggestions of other tools the could randomly generate points in this manner would also be helpful.

Thanks you in advance, 

Casey Davis.

[DanPatterson]

It is hard to tell whether you have excluded all the other features and dissolved that one feature that you are working with.

Given what I see and from the help topic... this still needs addressing

Random points may be within the minimum allowed distance if they were generated inside or along different constraining feature parts.

[FDavisIV]

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@DanPatterson wrote:

It is hard to tell whether you have excluded all the other features and dissolved that one feature that you are working with.

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Thanks Dan, I can try to elaborate. I am working with the Nation Hydrography Dataset Plus, which depicts and describes waterbodies in the United States. River networks are presented as a series of small segments. So, a single river may be broken up into 15-30 short segments, and the same is true for all tributaries of that river. I have selected the river segments that concern me and have either merged them using the modify features pane or dissolved them together using the Pairwise Dissolve tool (the result is the same via either method). This yields a feature class that contains a single feature (as in, one row on the attribute table) which represents all of the rivers that concern me. It is a large line feature that branches in several places. 

Attempting to generate random points using this feature class as the "constraining feature class" of the Create Random Points tool causes the problematic effect described above, where points are much closer together than specified.

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@DanPatterson wrote:

Random points may be within the minimum allowed distance if they were generated inside or along different constraining feature parts.

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Perhaps I just don't understand what "constraining feature parts" are in the context of this tool. It is my intention that there is only one "part" to be considered, hence the merging/dissolving.

I apologize if a lot of this is obvious, but I'm trying to be as descriptive as possible. I hope I've answered your question, let me know if I can provide any more information. 

[DanPatterson]

How Dissolve (Data Management) works—ArcGIS Pro | Documentation

can create multipart features, so where a river branches into two tributaries, that would be a multipart and cause problems.  I would test what happens If you manually unioned/mergedthe polyline segments along a river stretch (not the tributaries off of it) .  Find a suitable stretch that is longer than your desired distance.

Also... hope you are using Web Mercator as your coordinate system, it is useless for any analysis involving distance and/or area

[DuncanHornby · Accepted solution]

The ArcMap tool RivEX can sample the river network in a fixed distance or randomly, check the help file out here. It is designed to over the branching issue you are attempt to deal with.

[FDavisIV]

In the end I was able to generate the random points using RivEX. The branches in the network were indeed the problem; no method of dissolving/merging/combining the segments allowed it to work. It's a shame there isn't an easy way to solve this problem in ArcGIS Pro. Anyway, thanks everyone for the assistance!