[Qgis-developer] Cutting lines with a polygon boundary

[Zoltan Szecsei]

Hi Dev,
I put the request for help out on qgis-user and to my surprise, no one 
came up with direct solution.
This suggests that a "crop" feature is missing, so maybe it could be put 
in as a low priority feature request?
The thread is still active, so you can see the replies from Andre Joost 
and Randal Hale there.

Thanks & regards,
Zoltan.

*qgis-user thread started 25th Jan at 14h51 (GMT+2):*

    Hi,
    I'm battling finding an easy way to cut some lines with a polygon
    boundary, and then deleting the line portions that are OUTSIDE the
    polygon.

    Scenario:

        4 separate SHAPE files with lines in them
        1 shapefile with one polygon in it.

    I need to cut the lines in all 4 shapefiles at the point that their
    lines intersect the polygon boundary. Thereafter I want to delete
    the line portions that are outside of this polygon boundary. In
    other words, to be able to crop multiple layers according to some
    polygon boundary.

    I would have thought this to be a trivial issue, but I have tried:

          * Vector Geometry Processing Clip, but it wants to extract the
            data inside the polygon and create a new file with the
            extracted data. (To be expected)
          * Plugin 'Clipper': I select my lonely polygon, and then
            activate one of the line layers (which is also in edit mode).
            The plugin seems to do nothing when I choose 'intersection'
            or 'clipping' preview, and when I choose 'clip' it tells me
            to select at least one feature (but my polygon is still
            selected.) The home-page link comes up as '404 not found'
          * Didn't notice anything in the Advanced Digitizing plugin.
          * CadTools and CadDigitize - no relevant facility found, but
            really nice 'Help' doc - thanks guys!
          * Feature 'Cut with Polygon from another Layer' deletes the
            pieces I want to keep.
          * Feature: 'Split selected features with line from another
            layer' is to some extent what I want, but I want '... with
            polygon from another layer'

    So, I eventually gave up and converted my polygon into a line layer,
    and used 'Split selected features with line from another layer', but
    this is incredibly tedious because:

      * It only does one layer at a time
      * I then have to select the line segments that I want to delete.


    So, does anyone know of a way to efficiently cut features in
    multiple layers using a polygon, and then to be able to select the
    pieces (multiple layers) that are either inside or outside the
    polygon, and then delete them?

    Regards & thanks in advance,
    Zoltan




-- 

===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services

P.O. Box 7, Muizenberg 7950, South Africa.

Mobile: +27-83-6004028
Fax:    +27-86-6115323     www.geograph.co.za
===========================================

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20150126/bd54a476/attachment.html>