When creating a polygon, how do I do it so that the lines are straight (90, 0 degrees, etc.) and when I create corners they can be right angles? For instance, how do I create a perfect square or rectangle?
I tried the suggested solutions but found the CADTools plug-in a bit too complicated to get a quick hang of it. Besides, this is a rather simple task.
Instead I found the plug-in Rectangles Ovals Digitizing￼ by Pavol Kapusta. The name is rather self explanatory and it works excellently. You can draw shapes from centre or by extent.
the CadTools plugin should do what you want. there is also an tutorial: http://www.catais.org/qgis/cadtools/ (especially look under "orthogonal digitzing")
Another solution is you use the plugin azimuth and distance. http://geotecnologias.wordpress.com/2012/02/03/criando-poligonal-por-azimute-e-distancia-qgis/
In order to create polygons or lines with specified lenghts en angles you need to enable the advanced digitizing panel. (View--panels-advanced digitizing)
Just add vector layer (lines or polygons) start editing and add feature. In the advanced editing window you can specify the angles and/or distances. To finish the sketch, click right mouse.
I tried the CADtools but I found it a bit complicated. Besides, this is a rather simple task.Instead I found the plug-in Quantum Aided Design(cad like commands in QGIS). The name is rather self explanatory and it works excellently. You can draw/edit/copy/ trim or offset etc..