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Create line segments from polygons using coincident boundary with another polygon? (Lake parcels)

GriffonGriffon Global Mapper UserPosts: 28Trusted User
Here's my challenge. I need to define the amount of frontage each lake parcel (polygon) has. I have lots of parcels, so I'm looking for a way to automate or mass-process them.

Here's the example before processing:

I can create a line from a selected parcel (or lines from all selected parcels), but then I have to individually delete all the unnecessary vertices in order to end up with a measurable segment. See below:

The problem is, that takes time, when it would be much easier to have a tool that deletes all vectors of the new lines that are NOT coincident with the lake, a separate polygon shape. For instance, the segment of the parcel above that is along the river (narrow slot coming in from the top) should be excluded from the measurement. Here's what it looks like in detail:

I've selected most of the vertices to be deleted, but there are still a few points extending up the river inlet that should be selected and deleted as well. Using the lake as a selection tool, then inverting the selection of vertices, or some similar process would be much quicker, especially considering there could be hundreds of parcels involved.

Currently I'm using GlobalMapper 14, but may install and try 18 to see if it has any tools.

Thanks in advance for any help.


  • GriffonGriffon Global Mapper User Posts: 28Trusted User
    In the paragraph between the 2nd and 3rd image, I meant VERTICES not vector (i.e., a tool that deletes all vertices of the new lines...).
  • MarshallMarshall Posts: 25
    I just tried to come up with a solution using "find intersection" and split functions, but to no avail.  I'll be following the post and hope someone finds a solution.  Good luck.  
  • GriffonGriffon Global Mapper User Posts: 28Trusted User
    Thanks for trying. Even after looking at newer versions of Global Mapper and their lists of features, it wasn't clear it could be done. I went through the process manually. One problem I encountered is that because the begin/end points of the polygon and therefore the lines sometimes occurred along the frontage segment, I had to knit the two parts back together again. Overall it was tedious, steady work.
  • sphillipssphillips Posts: 210
    I tried a workaround with partial success. I converted the parcels to line features first, then created a small buffer from the lake polygon with a 0.1m offset (could be less though). I used this buffer with the Crop command to remove the lines outside the buffer. This leaves just the lines you need but with the 0.2m additional length per line. The only issue was that there were a few lines that were split for some reason.
  • GriffonGriffon Global Mapper User Posts: 28Trusted User
    Coming back to this thread after more than 2 years!

    Thanks for the idea, I'll give it a try. I think some of the splits in the lines that you describe, sphillips, have to do with the parcels themselves, the order of the vertices or something.

    My workaround has been as follows:

    1. convert the parcels to line features
    2. turn off the ability to select areas under Configuration, Vector Display
    3. show vertices (Shift-V)
    4. manually selecting all vertices that are not coindent with the lakeshore
    5. deleting vertices, by right clicking

    The clean up work is tedious. Some parcel lines are now connected between what should be beginning and endpoints. I have to split lines at interior points at the true endpoint, and sometimes combine split lines.
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