topic Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3 in Geoprocessing Questions

Thiessen Polygons Not Generating Continuous Tessellations in 10.3

GerryGabrisch — Wed, 18 Nov 2015 21:53:14 GMT

I noticed that the Create Thiessen Polygon Tool in ArcGIS 10.3 is not producing a continuous irregular tessellation across the analysis area.

The resulting polygons have gaps and overlaps as confirmed by topology! I have not noticed this on other versions of ArcGIS.

Can anyone confirm that this is happening on their installation of ArcGIS 10.3? Is there a fix, or does anyone have a script to replace Create Thiessen Polygons that works correctly?

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

DanPatterson_Retired — Wed, 18 Nov 2015 22:04:54 GMT

Gerry My ArcScripts mirror... Triangulation tools, shapefiles as input and output, should work, let me know if it doesn't

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

GerryGabrisch — Wed, 18 Nov 2015 22:28:06 GMT

Thanks, but it threw an error.

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

DanPatterson_Retired — Wed, 18 Nov 2015 22:41:11 GMT

A duplicate point ... I will have to check version numbers since I downloaded it from the beta site and I had corrected that, so if you have duplicate points you will have to wait...sorry

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

GerryGabrisch — Wed, 18 Nov 2015 23:48:47 GMT

I see that there are spatially duplicate points but with different attributes! That might be a problem.

I have contacted the data creator to sort out the differences.

Create Thiessen Polygons did not care if there were spatially duplicate points. I guess if you are going to be doing some coding, and want to produce a better tool, let the user know there are spatially duplicate points as a guard against such a thing.

Thanks for throwing the error triangulation tools!

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

DanPatterson_Retired — Thu, 19 Nov 2015 00:01:28 GMT

Gerry, I found that removing the duplicates, although not necessary, greatly improved performance and I have it included in the version (and will find it when I figure out where it went). The duplicates, should however, get dumped...even if silently... so as to avoid division by zero and other computational errors The attributes are not relevant in the implementation and they get dumped immediately.

On a lark...if you can identify the duplicates and remove them, try the inhouse tool on that dataset and see if you misaligned edges magically align. I did find a bug in qgis's implementation a few years ago, but it dealt with funny math beyond the convex hull of the input points.

Anyhow, if I get some time tonight or tomorrow, I will track down my latest and post it (too many machines in several locations)

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

curtvprice — Thu, 19 Nov 2015 03:15:32 GMT

How large is the gap?

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

GerryGabrisch — Fri, 20 Nov 2015 18:10:18 GMT

Curtis, in this case the gaps and overlaps are a few feet over polygons that are 10 to 12 feet across.

I did get confirmation from ESRI that this is a bug and will be fixed in 10.4.

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

DanPatterson_Retired — Fri, 20 Nov 2015 18:50:22 GMT

Gerry ... coming soon...I am having to port from python 2 to python 3, so it affected anything using "cmp" which was abandoned in version 2 so it can be used in ArcGIS Pro as well.

The duplicate point issue has also been solved regardless of input feature geometry. If duplicates are removed, I have had no problems with all the test cases I have run it on. I am assuming that you are using points as input? If so, just remove duplicates. I am also making it more generic so that it doesn't matter what the input geometry is. All features are converted to points, then all duplicates removed.

So if you are in a pinch, remove your duplicate points. In any event, I will post my version long before 10.4 comes out.

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

GhislainPrince — Fri, 20 Nov 2015 23:19:01 GMT

Hey Gerry,

can you share the gpk of your original case that produces gaps?

Or open a ticket with tech support. We'd like to look at this case.

thanks

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

GerryGabrisch — Mon, 23 Nov 2015 18:30:26 GMT

Ghislain,

Thanks for looking into the issue.

I have attached the gpk to this response.

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

DanPatterson_Retired — Mon, 23 Nov 2015 19:08:19 GMT

Clam Art

Well, you are going to have one H of a time trying to do that point distribution all at once.

In short, my toolbox didn't generate errors...don't know why yours did.

Shapefile in ... shapefile out as indicated in the tool help (for a litany of reasons)

The algorithm is Steve Fortune's original in case Ghislain is interested....I kept it old school without modern data structures, since it is a thing of beauty.

I just did one portion and had no issues except for the fact that

the distribution is hardly ideal for Voronoi or Delaunay triangulations
the coordinates are Geographic making the results essentially useless since the triangles etc are not geodesic

having said that, here are a few images and a package for you to examine. If you can play with the data and show me where you were getting the gaps, I can examine further (hope the mpk works... if not, I will zip and ship)

ADDENDUM

I am also guessing that is the coordinate system aka Geographic that is causing the problem

Re: Thiessen Polygons Not Generating Continuous Tessellations in 10.3

GerryGabrisch — Mon, 23 Nov 2015 21:40:08 GMT

Thanks for your help, Dan. Rest assured, I have a polygon layer that represents the bounding area of the survey that I will use to clip the Voronoi polygons with.

Projected - Geographic coordinate system? I had no idea this would make such a big difference in the resulting polygons. I have projected the data and re-created the Voronoi polygons and the gap and overlap problems went away. Best to read the fine print!

Problem Solved.