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Re: [jts-dev] Dimension of a MultiPoint
  • From: Phil Scadden <P.Scadden@xxxxxxxxxx>
  • Date: Mon, 23 Nov 2020 21:06:27 +0000
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  • Thread-topic: [jts-dev] Dimension of a MultiPoint

Concave hulls though involve decisions on what constitutes a point within the hull versus a point on the hull which is very application dependent. The routine gives you parameters to control this but I found it quite a complex  process tuning it for my needs.

 

From: jts-dev-bounces@xxxxxxxxxxx <jts-dev-bounces@xxxxxxxxxxx> On Behalf Of Kay, Jim
Sent: Tuesday, 24 November 2020 09:54
To: JTS project developer mailing list <jts-dev@xxxxxxxxxxx>
Subject: Re: [jts-dev] Dimension of a MultiPoint

 

 

Note: External sender:

You need to use “org.locationtech.jts.hull.ConcaveHull”

This is not in the core code, but can be found

 

https://github.com/locationtech/jts/blob/master/modules/lab/src/main/java/org/locationtech/jts/hull/ConcaveHull.java

 

Jim

From: jts-dev-bounces@xxxxxxxxxxx <jts-dev-bounces@xxxxxxxxxxx> On Behalf Of Afonso Henrique Sampaio
Sent: 23 November 2020 20:42
To: JTS project developer mailing list <jts-dev@xxxxxxxxxxx>
Subject: Re: [jts-dev] Dimension of a MultiPoint

 

Unlike the convex hull, the boundary can shrink towards the interior of the hull to envelop the points.  So

Boundary:                     ConvexHull:

    p1 ---------p5             p1------------p5

      \              |                |                 |

       p2          |                |                 |

     /               |                |                 |

    p3 ---------p5             p3------------p4

 

In the application we are developing, the edges (p1,p2) and (p2,p3) are also of interest...

 

Many thanks for the prompt response!
Afonso.

 

On Mon, Nov 23, 2020 at 9:28 PM Sandro Santilli <strk@xxxxxx> wrote:

On Mon, Nov 23, 2020 at 09:17:56PM +0100, Afonso Henrique Sampaio wrote:
> Dear,
> perhaps a silly question, but I'm new using JTS. I have a set of
> coordinates (x,y), and create a MultiPoint from a
> corresponding CoordinateSequence. Now, the dimension of this geometry I get
> by getDimension() is 0, and thus getBoundary() returns an empty Geometry.
> How then can I obtain the boundary of a set of points?

You're probably looking for Envelope, or ConvexHull

--strk;
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