[MapProxy] Caches, Grids & Coverage help

Oliver Tonnhofer olt at omniscale.de
Tue Jul 31 05:55:22 PDT 2012

On 31.07.2012, at 04:08, Benjamin Wragg wrote:
> I have a quick question about caches & grids and how they work with coverages. We have 3 areas we need to pre seed from one source tile server, but have different levels for each area. This will then be served out via a WMS layer with the seed_only:true setting. As an example, we would like the whole world at levels 0-2, one small country at 0-10 and another small country at 0-12. At first I set this up as 1 source, 1 cache and 1 grid. The grid was defined with num_levels: 13 (to accommodate the country with levels 0-12).  I then seeded the 3 different areas using coverages with the levels "to:" setting appropriate for each area.
> The problem I'm having is when I access this via WMS, if I zoom in on a area other than the areas we pre seeded to levels 10 & 12, as I zoom in the image soon disappears and I get a blank screen rather than it keeping the world image of level 2 visible the entire time. I assume this is because of the num_level 13 setting? i.e its trying to load up a level of that area which isn't available as we only pre seeded that area with levels 0-2.

It will try to load tiles for level 4, 5, etc. but will return an empty response if there is no tile stored. There is no option to use tiles from higher levels in this case.

> So to make this work what should I do? Do I :
> 1) create 3 grids, all identical just with a different num_level settings and have 1 cache which has a grid setting of:
> grids: [my_grid_one, my_grid_two, my_grid_three]

That doesn't work if they all share the same projection.

> 2) create 3 caches each with their own grid and then have 1 layer with its source set to [cache_1, cache_2, cache_3]

That should work.


Oliver Tonnhofer    | Omniscale GmbH & Co KG    | http://omniscale.de
http://mapproxy.org | https://github.com/olt | @oltonn

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