[Qgis-developer] Improving QGIS Measure tool

Alexander Bruy alexander.bruy at gmail.com
Mon Nov 8 15:41:23 EST 2010

Hi devs,

We want to improve the QGIS measure tool to make possible distance
measurements in unprojected sessions when latlong data is loaded.
This is helpful when you don't want to project your data for some
reason, but still would like to measure distance in meters. For this
we were willing to use QgsDistanceArea::computeDistanceBearing()
which already has Vincenty formulae.

But, at this time QgsDistanceArea::computeDistanceBearing() requires
projection and ellipsoid to be already set before calling it.

We want to modify QgsDistanceArea::computeDistanceBearing() to add
ability to do measurements without reprojection or coordinate transform,
but passing Ellipsoid as one of the parameters. But we unsure is this
safe because Measure tool doesn't create it's own instance of
QgsDistanceArea but get it from map renderer.

Any thoughts on this?


Alexander Bruy

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