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I'm currently using QGIS basically to trace a bunch of polygons to show individual ponds from google maps. Some of the geometries can be pretty oddly shaped and using the nodal digitizing tool gets pretty tedious if you have thousands of ponds.

Is there a better way or software for drawing? I'm imagining something like in photoshop where you can click and hold while tracing the shape instead of needing to click and line up each node.

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  • While not open source nor free, you can use OCAD for that. It has got a lot more sophisticated tools for digitizing (however still manual), at least compared to ArcGIS (which I'm more familiar with). Especially curved lines are better supported. There is a learning curve (!) though...
    – Martin
    Commented Nov 25, 2014 at 9:18
  • More sophisticated tools means "no topology control" like other CAD softwares
    – Sergio
    Commented Nov 25, 2014 at 9:26
  • The only partial solution I know is a paid one, R2V... Commented Nov 25, 2014 at 16:53
  • Tools for this have gotten better in QGIS now
    – BillW
    Commented Feb 12, 2016 at 4:06

1 Answer 1

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You can use the Freehand editing plugin (not to be confused with the trace edit tool). Get this by installing it through the plugins menu option.

Another option would be to use edge detection in the Processing toolbox (Have a look at tools in GRASS and Orfeo. SAGA maybe has one too I forget). The downside of this is that it will detect all edges. What I might be tempted to try is to open the image in GIMP or Photoshop and use the magic want tool to select my ponds automagically and in a new layer colour these selected area a single simple colour (e.g. red). Then save the new image as a tif and create a TFW file (based on the original image just rename the TWF to match your ponds file). Bring this in to QGIS vectorize the pond polygons. I'd then generalize the vector ponds. After that it is a case of tweaking pre-existing nodes to ensure a good fit to the original raster.

If you have thousands of ponds, any approach, even edge detection will be tedious.

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