6

I have a dataset of horizontal polygons, which have a vertical distance of 175 meters to each other. These polygons mark certain areas. I would like to have one polygon that covers all the area and doesn't have these blank stripes in it. Basically I want to sort of buffer the polygons, but only vertically, so that they connect to one big polygon.

I am working on ArcGIS 10.3. with a Standard License, but have also QGIS. I have tried to Buffer but I only managed to Buffer in all directions, so that the shape was lost.

Does someone know how to do this?

Here is a sample of the data:

enter image description here

5
  • 3
    Welcome to Geographic Information Systems! Welcome to GIS SE! We're a little different from other sites; this isn't a discussion forum but a Q&A site. Your questions should as much as possible describe not just what you want to do, but precisely what you have tried and where you are stuck trying that. Please check out our short tour for more about how the site works. – Ian Turton Oct 9 '20 at 7:54
  • 2
    What GIS software are you using to try and do this? What have you tried? – PolyGeo Oct 9 '20 at 7:55
  • 2
    You need some concave hull tool, I don't think this is available with a standard licence – J.R Oct 9 '20 at 8:49
  • @J.R. ok is there a similar tool in QGIS maybe? – Hannes Oct 9 '20 at 9:39
  • Yes, QGIS has two concave hull tool, alpha shape (work only with points) and k-nearest neighbor (use nodes for lines and polygons). I don't know enough about these two algorithm to recommend one or the other for your case. – J.R Oct 9 '20 at 10:58
5

As you are willing to use QGIS there is a way :

  1. Use the "Densify by interval" tool to add vertices to your polygon (choose the interval depending polygon size, more vertices will get result closer to original polygon but will make computing time increase). This step allow the convex hull to be computed not only at the corner but also from the edge of polygons

  2. Use the "Extract vertices" tool on your densified polygon

  3. Run the "Concave hull (alpha shape)" on the extracted vertices, dont forget to uncheck the "Allow holes" option and adjust the Threshold to get your desired result, see below for result with a threshold of 0.2 (best result for me with this number of vertices)

  4. Optional : edit the resulting concave hull to get a shape closer to your need, enabling snapping to the extracted vertices will make this easier.

enter image description here

2

Solution below requires 3D analyst license.

  • Densify polygons
  • Use them (mass points) to create TIN
  • Delineate TIN Data Area

Solution below is a result of 2 iterations:

enter image description here

Extract and dissolve TIN triangles to get polygon(s).

Much nicer result can be achieved by using Near Table, but it requires advanced ArcGIS license.

1

Using QGIS 3.14.16, I tested the Concave Hull (k-nearest neighbor) tool suggested by @J.R with neighboring points = 20.

Here's my original polygon layer:

enter image description here

And here's the k-nearest result:

enter image description here

1
  • 1
    Result shows convex hull of them. It is I line in arcgis field calculator in absence of advanced license. – FelixIP Oct 9 '20 at 21:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.