[QGIS-Developer] QGIS server issue: bounding box issues

[Andreas Neumann]

Hi QGIS (server) devs,

We came across issues around calculating bounding boxes in QGIS server.

1. Layers with only one point feature:

If a layer contains only one single point feature, QGIS server 
calculates a bounding box where the minx equals maxx and miny equals 
maxy, so resulting in a bounding box without a width and height. Sounds 
logical to QGIS server developers, but combined with the fact that QGIS 
server doesn't take into account rendered symbol sizes (another issue we 
have, see issue nr 2), it means that no WMS client will ever see this 
one single symbol rendered, which can't be the solution here ...

2. Layer bounding boxes do not take into account rendered symbol sizes:

Please have a look at 
http://www.carto.net/neumann/temp/qgis_server_bounding_box_issue.png - 
The green rectangle and the green arrows are not part of the QGIS server 
rendering, but they are added as an annotation to the rendered QGIS 
server graphics, to highlight the issues.

Here we have the issue that QGIS server only uses the "raw" geometry of 
point symbols without taking into account rendered symbol sizes. Now, I 
do understand that calculating symbol sizes is scale dependent and there 
is no single solution to that, but again, I think the current behavior 
of QGIS server (simply cutting off symbols at layer bounding boxes) is 
not a good and nice behavior. At least, I think the author of the WMS 
service should have a chance to define an extra margin to be added to 
the bounding boxes of the raw geometries of the point layer, either as a 
"per project" or "per layer" QGIS server configuration.

@Andrea: I wonder what Geoserver does in such cases?

Any thoughts how to solve these issues? The current behavior of QGIS 
server is not satisfactory to me, for both cases.

Thanks for your replies,

Andreas