[Qgis-developer] Custom composer items?

Chris Crook ccrook at linz.govt.nz
Sun Feb 28 17:36:50 EST 2010


I'm wanting to add scale information for symbols to composer.  These are arrow symbols representing vector fields, so I want to be able to show in the composer generated page what the scale of the arrows is (ie how long an arrow represents a 5cm offset at a point, or whatever).

Logically this would be a custom composer item, but I cannot see any way to create a custom item, either in C++ or in Python (my preference!), without modifying the base composer classe(s).  Can anyone confirm this?

A slightly less desirable approach would be to draw the scale information onto the map item in composer.  This would constrain the placement - it would be nicer to be able to place it arbitrarily as other widget items.

In the main Qgis window I draw this scale information onto the map canvas in response to the renderComplete signal, in the same way as the scale bar or north arrow, but I don't think there is an equivalent event when the composer map item is drawn?  So I can't use that approach to draw onto the canvas...

I think I may be able to draw the scale information by adding a custom map layer.

Can anyone suggest better approaches, or point me to something obvious I've missed?

Many thanks



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Thank you.
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