On 7 March 2017 at 16:31, Mark Johnson <mj10...@googlemail.com> wrote: >>> I'm confused - what is missing? > > The topic here is that when using MapUnits > - where the MapUnits are degrees > that a constant value (valid around the world) is not possible. > > If you set this to 5 (intended as meters on the map) > - the further you zoom in, the circle will get bigger always showing an area > of 5 meters > > If the Map is switched to WSG84 > - then you will get 5 degrees and not the desired area of 5 meters > --> which for my area would be 0.000075, at the equator 0,000045 and in you > area something different > > Since the source and destination crs are unknown when this attribute value > is being set > - one cannot assume that one or the other use meters and therefore cannot be > used
It might be unknown at the time of setting that value - but it's certainly known at the time that QgsRenderContext::convertToPainterUnits or similar is called! So you add a new QgsUnitTypes::RenderUnit enum value for MapUnitMeters, and then if that unit is encountered by QgsRenderContext::convertToPainterUnits you could do the calculation from metres -> real map units -> painter units then. (The conversion value could be cached in the render context to avoid multiple coordinate transforms) Nyall _______________________________________________ Qgis-developer mailing list Qgis-developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
