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I am trying to draw two squares on a 45-degree angle and then merge them using PostGIS to edit. QGIS can draw squares but only on a perpendicular plane (eg, 0, 90, 180), and I need to be able to draw at different angles (eg, 45-degrees).

Thank you!

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The problem description is still too vague to offer you good answers. Please provide a description and sketches of what you are trying to do. Then we can suggest relevant tools for the job. –  underdark Nov 14 '12 at 18:49
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3 Answers 3

I googled "qgis diamond" and found that there is a plugin that will supposedly do this. Go here: http://pyqgis.org/repo/contributed and scroll down to "Rectangles, Ovals, Diamonds : 0.1.7". Haven't tried it though.

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It works just fine. I use it regularly. See Mapperz link in the comments above. One small idosyncracy seems to be if you have edited or created new geometry, even when you save it, the plugin doesn't always seem to recognize the changes. You can get around that by just removing and re-adding the relevant layer. Otherwise, it works like a charm. –  MappaGnosis Nov 15 '12 at 13:16
    
Thank you very much for your comments everyone. One more question - I am open to using other free GIS programs (not just QGIS), what is the most user-friendly application to quickly change vector shapes (buildings mostly) and merge/dissolve at the end? I need to be able to go through a tile in under 2 minutes, to get rid of any footprints that are actually trees, roads, etc. (anything that is not a building), and to correct any footprints when compared to its corresponding imagery. Thank you! –  Rachel Nov 15 '12 at 16:19

That's default QGIS behavior: Editing and PostGIS connections are available in the core application.

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One more correction that I received - the tool has to be able to edit from PostGIS... –  Rachel Nov 14 '12 at 19:17
    
Please clarify exactly what you want to do, then we worry about PostGIS. –  underdark Nov 14 '12 at 19:18

What you want to do is called Digitizing or Editing. Have you looked at the digitizing toolbar? Also have a look at the Digitizing an existing layer section from the Qgis user manual.

You can create new features in various types of vector layers, including a PostGIS layer.

You should add your PostGIS data to your map, and then toggle editing. After that you can start digitizing and adding new features.

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Thank you very much. I just posted another comment which kind of narrows down what I need. Thanks! –  Rachel Nov 15 '12 at 16:20

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