topic Re: Draw a polygon automatically around points, in Geoprocessing Questions

Draw a polygon automatically around points,

MajdoleenO_A__Awadallah — Tue, 16 Feb 2016 10:21:07 GMT

Draw a polygon automatically around points,

I am looking for a way to draw a polygon automatically around points that have similar value in one field of the attribute table.

For example, in the screenshot below, I wanted to draw a polygon around the points that have class B, and to have the points inside the curved polygon but not as if they are at the boundaries (not like minimum boundary geometry tool).

Thank you in advance,

Best,

Majdoleen

Re: Draw a polygon automatically around points,

XanderBakker — Tue, 16 Feb 2016 11:25:29 GMT

You should probably use Thiessen polygons to get a simular result. See Create Thiessen Polygons—Help | ArcGIS for Desktop followed by dissolving on the attribute. Create Thiessen Polygons requires an advanced license, but Dan Patterson has created a tool for Basic license that creates them too.

Dan Patterson, can you add the link to that tool? Thanks!

Re: Draw a polygon automatically around points,

MajdoleenO_A__Awadallah — Tue, 16 Feb 2016 11:35:29 GMT

Thank you Xander, but my point here that I want to produce smooth curved polygons around the points that have similar value as shown in the screenshot.

Best,

Majdoleen

Re: Draw a polygon automatically around points,

XanderBakker — Tue, 16 Feb 2016 11:39:53 GMT

You can apply a negative buffer after the dissolve step.

Re: Draw a polygon automatically around points,

DanPatterson_Retired — Tue, 16 Feb 2016 11:48:23 GMT

Xander...

Called... Triangulation Tools ...since it does both Delaunay and Voronoi

Re: Draw a polygon automatically around points,

XanderBakker — Tue, 16 Feb 2016 11:54:09 GMT

Or better yet, use the Smooth Polygon—Help | ArcGIS for Desktop tool (Advanced license required)

Re: Draw a polygon automatically around points,

XanderBakker — Tue, 16 Feb 2016 11:54:48 GMT

Thanks Dan, I will bookmark it (include it in my local Wiki)

Re: Draw a polygon automatically around points,

XanderBakker — Tue, 16 Feb 2016 12:03:59 GMT

I do wonder how you are going to manage the points identified with the letter "A". If I create Thiessen polygons the "C" polygon does not connect since the A points are nearer:

as you can see here (after dissolving):

Applying a negative buffer and Smooth polygon with the PEAK setting doesn't really get us there:

The BEZIER setting gets a little closer, although it still isn't the result you sketched.

Re: Draw a polygon automatically around points,

MajdoleenO_A__Awadallah — Tue, 16 Feb 2016 12:18:25 GMT

Thank You, It is very helpful, but the only thing that missing here is: I want all the A's in one single polygon!!

Re: Draw a polygon automatically around points,

DanPatterson_Retired — Tue, 16 Feb 2016 12:22:24 GMT

The A's can constitute a multipart polygon... that is a polygon that consists of discrete separated areas but share a common record in a table. There is no way that you are going to get the geometries together into one physical polygon... unless you draw it yourself ...

Re: Draw a polygon automatically around points,

XanderBakker — Tue, 16 Feb 2016 12:30:56 GMT

For the B's and C's there may be another option using another tool Dan Patterson created: the minimum spanning tree. Create the connected network for each group of values and buffer the lines, and smooth the dissolved polygon...

Re: Draw a polygon automatically around points,

DanPatterson_Retired — Tue, 16 Feb 2016 12:38:21 GMT

Spanning Tree Tools you have to understand how they work in order for them to be useful

Re: Draw a polygon automatically around points,

MajdoleenO_A__Awadallah — Tue, 16 Feb 2016 12:43:08 GMT

Thank you Xander and Dan, but I don't want to do such a work like this manually!!!

Re: Draw a polygon automatically around points,

DanPatterson_Retired — Tue, 16 Feb 2016 12:48:27 GMT

spanning tree workflow as per Xander's suggestion... it is not going to be a button push since you have to understand how spanning trees are created. I can guarantee you right now, there is no way you are going to get all the groups into separate polygon without creating multipart shapes... that is a manual approach or ArcWish

Re: Draw a polygon automatically around points,

smevans88 — Thu, 04 Aug 2022 11:47:01 GMT

Thanks Xander,

I ran into a similar issue. I was trying to go from points to line, using a specific attribute of the points layer

I have foot by foot points along a line. I have sectioned out the points by an specific attribute, using the thiessen polygons. Then the dissolve tool helped to lump the similar polygons together.

Now, I can clip a base mainline (for railroad) polyline layer by the polygons. Perfect solution.

Thanks!

Scott