[Qgis-user] Real Mask functionality in QGIS?

[Régis Haubourg]

Hi Hilpers,
I funded the mask plugin and can explain what it does. In my needs, I
didn't not want it to clip the geometries (like the mapinfo clip tool)
because I preferer really when users can see the whole map, masked with
transparency or blending mode. This also does not add any geometry
processing, which can be really heavy for clipping all the displayed object
in a map.
Nevertheless, We extended Mask to be able to filter labels and display them
only if the features fall inside the mask zone (with options on spatial
operators used). We lacked the ability to compute labels only in the part
of the object that is inside the mask (for instance a great river crossing
the zone can be labeled outside the zone), so we added that in latest
plugin versions, and it reveals to be performant since when it computes a
lot of spatial relation, it also make life easier to the labeling engine,
and turns to be fastest in the end (not always).

We chose to stop the plugin dev here and produce QEP to port that inside
QGIS core. This assumes quite a lot of changes :
 - find a way to store data in or along the project (we currently rely on
memory layer saver plugin)
 - Add ability to draw label on a different geometry than the displayed one
(such as a smoothed geometry for a watercourse, or a clipped part of a
polygon with mask zone)
- take the opportunity to improve labeling by the way with native
connectors and easiest manual placement

You can find those QEP here:
https://github.com/qgis/QGIS-Enhancement-Proposals, tickets 27, 47, 46, 62

I since left my job and can't help with funding anymore, but from what I
know some funds will be available at least for the label improvements. If
you're willing to help or fund, I'll be glad to help coordination with
other funders and developpers to fully port a masking feature, and maybe
add your use cases in it.

Cheers
Régis

2017-03-09 12:42 GMT+01:00 hilpers <orchestra-mur at web.de>:

> It should work dynamically, without processing your data, yes.
> I know this functionalityx from ArcMap and Mapinfo, where the user can
> specify one layer to serve as masking layer which then hides/masks out all
> features of user-specified layers within the same project/ data frame
> (Arcmap). I guess this works through spatial relationship filters but I am
> not sure.
>
>
>
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