Hi Bill
Thank you very much for the usefull WFS extensions! Your patch is
applied to master now (that was approach 2. I guess?).
Seems to me approach 2. is good in a zoom-in scenario whereas approach
3. is also good in a pan scenario (e.g. panning back to areas already
visited). So my favorite one is 3.
In longer term, it would be cool to have an intelligent caching strategy
considering the used amount of memory and the already visited areas (and
that could also be used as cache for other provider types, e.g.
postgres, shape, ...).
Regards,
Marco
On 26.12.2011 10:26, Bill Clay wrote:
Hello, all.
I've been working on WFS bug 4604 and feature request 4280 as my first
attempt to contribute as a QGIS developer. I have working code for
three different approaches. Which one should be completed and used?
1. Minimal patch. Gives you a choice between caching the ENTIRE WFS
layer for the life of the layer (slow layer creation for big layers on
remote WFS providers) or freshly fetching WFS extents each time they
are rendered (slow on each WFS layer rendering).
2. Medium patch. If you choose not to cache the entire layer, an
expanding extent is cached, starting with the first rendered extent.
Each time a new area is rendered, the cached extent expands, combining
the new canvas extent with the previous WFS layer extent. On each
expansion, the cache is discarded and the expanded extent fetched
fresh. After a short "training period," local pans and zooms are fast
because they work from the cache without requiring a new WFS fetch.
3. Maximum patch. The "expanding cache" approach of nr. 2 above, but
instead of replacing the cached extent each time the extent expands,
we fetch only the NEW areas of the expanded extent (i.e., 1-4
rectangles around the perimeter of the cached layer extent) and ADD
their features to the cache (discarding duplicate features). Faster
rendering of new areas than nr. 2 when there are many features, but
slower for small layers because a separate HTTP GET is required for
each of 1-4 new areas.
Is there a "typical" WFS user? Do they use WFS layers with many
features? If so, patch 3 might be best; otherwise maybe patch 2.
Best wishes for the holidays!
Bill Clay
_______________________________________________
Qgis-developer mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/qgis-developer
--
Dr. Marco Hugentobler
Sourcepole - Linux& Open Source Solutions
Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
[email protected] http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee
_______________________________________________
Qgis-developer mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/qgis-developer
