idea Concave Hull and/or Alpha Shapes geoprocessing tool in ArcGIS Pro Ideas

Concave Hull and/or Alpha Shapes geoprocessing tool

NathanWarmerdam — Thu, 26 Aug 2010 22:44:29 GMT

While I know that there are places to find concave hull and/or alpha shape algorithms, it seems like the biggest/best/most pervasive GIS company in the world would have this tool or a set of tools to do this kind of operation. My suggestion is to add a concave hull tool as well as an alpha shapes tool for creating a bounding polygon around a set of features.

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

Bruce_RHarold — Thu, 26 Aug 2010 22:59:32 GMT

Hi

If you have ArcInfo, try the Aggregate Points/Polygons tools in the cartography>generalization toolset.

Also, please keep a watch on the geoprocessing gallery in September 🙂

Regards

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

NathanWarmerdam — Fri, 27 Aug 2010 15:12:30 GMT

Hey Bruce,
Thanks for the tip, that looks useful but I think you need to spruce up the doc a little bit. What methodology is used? The second usage tip implies that there are some limitations. A bit more discussion would be helpful.
So what should I expect in the geoprocessing gallery? Cool script tool that works at 9.3?? 🙂
Nathan

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

Bruce_RHarold — Wed, 01 Sep 2010 18:45:44 GMT

Hi Nathan

Thanks for the feedback on the GP tools.

The item we hope to put on the GP gallery is an arcpy script tool, easily backported to use arcgisscripting. We're just going through the permissions process.

Regards

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

DanPatterson_Retired — Tue, 14 Aug 2018 21:57:07 GMT

so long.... so little movement....

at least an interim solution until basic algorithms are implemented... I know... low market share.

Concave Hulls ... for arcgis Pro

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

PhilLarkin1 — Wed, 27 Oct 2021 18:40:05 GMT

Still dreaming of an out-of-the box tool from ESRI.

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

feralcatcolonist_old — Wed, 20 Apr 2022 12:41:21 GMT

I think it'd be great to see this tool get added.

Concave hull as an option in Minumum Bounding Geometry tool

KerstinGeitner — Fri, 01 Jul 2022 13:07:52 GMT

In the Minimum Boundary Geometric tool, there are 5 different options for geometry type. It would be really useful for me if I could choose "Concave Hull" as an option.

I am working with Lidar data that are points, showing the area of a mussel bank. In order to be able to work further with the data, eg. calculate the area, calculate area of different depth strata, I need to be able to delimit the area closer than what is possible with the convex hull option or others. It is possible to do so with python or add-on products or other GIS software. I think it should be possible to do so in the standard ArcGIS Pro interface.

In the attached map, you can see the points in different blue color groups, it is the black line, that delimits the area polygon, I would like to have e tool for.

Re: Concave hull as an option in Minumum Bounding Geometry tool

DanLee — Fri, 01 Jul 2022 15:42:07 GMT

Concave hull is different from the geometry types produced by Minimum Bounding Geometry (MBG). Each geometry type from MBG is uniquely defined. But a concave hull is not unique and depends on a tolerance that controls how much the shape concaves.

What you need may be done by Aggregate Points tool. The larger the aggregation distance is, the more generalized shape you get.

https://pro.arcgis.com/en/pro-app/2.9/tool-reference/cartography/aggregate-points.htm

This tool may produce polygons with holes. If you don't want the holes, you can use Eliminate Polygon Part to get rid of them.

https://pro.arcgis.com/en/pro-app/2.8/tool-reference/data-management/eliminate-polygon-part.htm

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

KerstinGeitner — Tue, 26 Jul 2022 09:06:05 GMT

Thank you so much for your reply, DanLee. The Aggregate Points tool was just what I needed. I only searched for concave hull in the tools, I never would have guessed to search for this name. It produces (largely) the same results as ET Geowizards for ArcGIS and QGIS Concave tools, when the same threshold values are used. Plus ArcGIS Pro handles the huge amount of points (+300,000) way better and faster.

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

DanLee — Wed, 03 Aug 2022 21:08:27 GMT

Hi KerstinGeitner,

Sorry for my delayed reply; I was on vacation last week. 🙂

I am glad Aggregate Points tool worked for you. There are various terms people use to describe this functionality, including concave hull, alpha-shape, etc. You can actually search by concave hull in the Geoprocessing pane to find the tool down a bit in the list. We can still improve the search keywords so people can find it more easily.

Thanks for your feedback. I really appreciate your comments about the good performance of the tool. Cheers!

Re: Concave Hull and/or Alpha Shapes geoprocessing tool - Status changed to: Closed

DrewFlater — Thu, 04 Aug 2022 23:09:26 GMT

A dedicated Concave Hull or Alpha Shape geoprocessing tool has not been developed and is not planned at this time.

The Aggregate Points tool can often be used to accomplish the generation of similar enclosing shapes.

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

KerstinGeitner — Mon, 08 Aug 2022 08:18:35 GMT

Hi DanLee,

thanks for your reply. I have an additional question. Is there a way to make a lot of concave hull areas from one point file based on an attribute? I can not find an option to use an attribute to group points in the Aggregate points tool.

I have a file with a lot of sampling stations that are being sampled every year. Since they are taken by boat it is not possible to do it at the exact same point, so we would like to calculate the area that is covered but each of the stations. I can convert the point file to a polygon file, but the picture I get is a bit blurred since I just want a outline around the stations and the stations are not necessarily in the order to make that possible, even though I could sort them by the year they are sampled.

Thanks in advance.

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

DanLee — Mon, 08 Aug 2022 15:28:42 GMT

Hi KerstinGeitner,

I am not clear about your description "I can convert the point file to a polygon file, but the picture I get is a bit blurred ..." Can you show a screenshot?

Currently Aggregate Points doesn't have the Aggregate Field parameter as Aggregate Polygons tool does. You can create a very small polygon around each point using Buffer tool, which carries over input attributes. Then use Aggregate Polygons tool with a desired Aggregation Distance and your station ID/attribute as Aggregate Field to obtain the needed polygons.

Would that work for you?

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

KerstinGeitner — Thu, 11 Aug 2022 07:50:35 GMT

Hi @DanLee,

Thank you so much. I made a very small buffer around my stations and then used the aggregate polygon tool. The resulting polygons are just what I needed to get to the next step in the research.

Again, thank you very much for your help, I really appreciate it.

Cheers

Kerstin

Re: Concave Hull and/or Alpha Shapes geoprocessing tool

Jennifer_Andrews — Tue, 25 Mar 2025 03:34:25 GMT

Has anyone found a simple and accurate way to produce concave hull/alpha shape polygons? I've spent a couple years trying to do this and in the wee hours of the morning, I finally got it. I ran it on my 100,000 points and the script accurately created concave hulls around these points that I told it to group by a particular attribute. If anyone else has a working method for this, I'd like to see it and compare!

FYI, I have zero training/education/experience in programming or code writing so I was very excited to see it run.

Jenn