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

Nyall Dawson nyall.dawson at gmail.com
Sun Oct 18 13:26:00 PDT 2015

Hi all,

I'm totally struggling to understand what the "Canvas Units" setting
in project properties is there for, and what it's ACTUALLY supposed to

Currently, it seems like a read-only property. Whatever you set it to
(regardless of whether or not OTF is enabled or not), it's always
reset whenever you reopen the properties dialog. But the broken
behaviour goes a lot deeper than just this.... looking at the code
it's very unclear what this setting is there for. I think it's
*supposed* to allow users to override the map units for the current
project CRS, but why would we want this? Changing it would result in
totally meaningless measurements....!

Unless I'm misunderstanding, this setting should be removed and
replaced with a label showing what the units are for the current

I'm trying to get to the bottom of http://hub.qgis.org/issues/11986
(Area calculation is wrong with OTF enabled), but even after reading
the source I'm struggling to understand how QGIS is supposed to be
handling this. And if a developer who CAN read the source has no idea,
how are normal users supposed to understand this? ;)

Any ideas on what the correct behaviour should be, please let me know
ASAP and maybe I can get this sorted before release.


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