MapInfo Pro

 View Only
  • 1.  Region of Points

    Posted 04-17-2023 14:03

    I have a collection of points (not shapes) that I would like to encompass in a region - is there any way to do this?  Thanks



    ------------------------------
    Rex Edwards
    CAMPBELL AVIATION GROUP
    Tysons Corner VA
    ------------------------------


  • 2.  RE: Region of Points

    Posted 04-18-2023 01:59

    Hi,

    Look at Spatial tab > Buffer > Convex hull.



    ------------------------------
    Uffe Kousgaard
    ROUTEWARE
    Roskilde
    ------------------------------



  • 3.  RE: Region of Points

    Posted 04-18-2023 13:01

    Thanks - that may work.  Below is the set of red dots I would like to draw around to create a "closest" polygon.

    Points closest to 3 airports


    ------------------------------
    Rex Edwards
    CAMPBELL AVIATION GROUP
    Tysons Corner VA
    ------------------------------



  • 4.  RE: Region of Points

    Employee
    Posted 04-19-2023 04:32
    Edited by Peter Møller 04-19-2023 04:32
      |   view attached

    Convex Hull is not always the "closest polygon". It is more like a rubber band around the points.

    Alpha Shapes can be used to create a polygon "close" to the points.


    Nyall Dawson created a MapBasic tool for creating these Alpha Shapes a decade ago.
    The source code can be found on GitHub.

    I took his source code and modified it slightly to make it work in MapInfo Pro 64-bit.

    I have attached a copy of the compiled file.
    Load it into MapInfo Pro, and you will find a new button on the Spatial tab in the Create group.

    Select the points you want to use, specify where to save the result and it will process the data.
    It will then show you a dialog like the one above.

    You can modify the Alpha Value. Larger values will use fewer "outside" points and smaller values will use more "outside" points.


    Click the Preview to see the change when modifying the Alpha Value. When you are happy with the result, use the OK to save the final polygon.



    ------------------------------
    Peter Horsbøll Møller
    Principal Presales Consultant | Distinguished Engineer
    Precisely | Trust in Data
    ------------------------------

    Attachment(s)

    zip
    alpha_shapes x64.zip   7 KB 1 version


  • 5.  RE: Region of Points

    Posted 04-19-2023 04:50

    Then it may be Spatial tab > Regions > Voronoi you are after. The final output will follow the line between red/green and red/blue closely, but the outer perimeter is going to a rectangle. You could clip the 3 voronoi polygons by a single alpha shape, based upon all points.



    ------------------------------
    Uffe Kousgaard
    ROUTEWARE
    Roskilde
    ------------------------------



  • 6.  RE: Region of Points

    Employee
    Posted 04-19-2023 05:13

    You can make the resulting Voronoi polygons follow an existing boundary. Select this boundary, make the layer editable, and set it as the target.

    This only works if you have selected a single polygon. This single polygon can however have multiple segments.

    Read more here: MapInfo Monday: Creating Voronoi Polygons from Points



    ------------------------------
    Peter Horsbøll Møller
    Principal Presales Consultant | Distinguished Engineer
    Precisely | Trust in Data
    ------------------------------