[Qgis-developer] Meaning of "Canvas Units" in project properties?!?

Nyall Dawson nyall.dawson at gmail.com
Tue Oct 20 03:57:05 PDT 2015

On 20 Oct 2015 9:36 PM, "Giovanni Manghi" <giovanni.manghi at gmail.com> wrote:
> > The thing is, I'm not convinced the area is wrong... it's just that
> > QGIS' handling of units with OTF on/off ellipsoid ON/OFF is extremely
> > confusing (ie, I don't even fully understand it).
> My understanding, at least until http://hub.qgis.org/issues/12057 , is
> that the confusing bit is that sometimes areas measured on an
> ellipsoid are smaller than the same ones measured on a plane, this
> because not all projections are conservative for areas. Differences
> are relatively small, of course if the area measured with OTF on
> differs of several magnitudes then there is probably something wrong
> (but do not seems the case anymore).

Yep, but that's expected/correct behaviour. Ellipsoidal area WILL differ
from planar area and will differ between ellipsoids. So no issue there.

> There is also the issue with measurements being always in m for
> projections in feet, this I can confirm after testing quickly (on
> master) the dataset of http://hub.qgis.org/issues/13209 (but
> transforming the result from square meters to acres give the right
> results).

Right, so that's more of a feature request/ui clarification. We need a way
of notifying users what units the area will be in and also allow them to
override this.

I think removing the broken canvas units from project properties is a
start, and maybe switching that to a selector for areal/distance unit
calculations. Can't be solved for 2.12 though.


> cheers!
> -- G --
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20151020/b461b3a0/attachment.html>

More information about the Qgis-developer mailing list