[mapserver-dev] RFC97: Dynamically Creating High Zoom-Level Tiles

thomas bonfort thomas.bonfort at gmail.com
Tue Apr 16 06:43:00 PDT 2013

if max is 15, you would only resample for levels 16, 17 and up, i.e. always
from a single tile using the common power-of-two grids (g, wgs84, ...) or
at the worst from 4 tiles for the other ones.

so z <= max-cached-level : usual behavior
z > max-cached-level : upscale from tiles where z=max-cached-level

clearer ?


On 16 April 2013 15:36, Stephen Woodbridge <woodbri at swoodbridge.com> wrote:

> On 4/16/2013 2:43 AM, thomas bonfort wrote:
>> Devs,
>> Please find RFC97:
>> http://mapserver.org/**development/rfc/ms-rfc-97.html<http://mapserver.org/development/rfc/ms-rfc-97.html>
>> A bit short for an RFC, but a bit too long for just a ticket... This RFC
>> basically allows serving tiles from high zoom levels by upscaling lower
>> zoom level ones at request time, thus avoiding to fill up the caches
>> with upscaled data.
>> Note that the RFC also provisions the usage of proxying these high
>> zoom-level tiles to the source WMS instead of reconstructing them from
>> the lower level tiles (use-case: the WMS is fast enough when zoomed-in,
>> but needs caching when far away). This isn't implemented yet, but should
>> be a contribution by the OpenWebBlobe folks in some future.
> Hi Thomas,
> I have a couple of questions, probably not enough coffee to get my brain
> turned on yet.
> Your goal is to produce up sampled tiles from tiles at the “maximum cached
> level” using the reassemble strategy.
> So if that is level 15, then at 14 each tile would need to resample 4
> tiles, and at 13 need to resample 16 tiles, and at 12 need to resample 64
> tiles, etc.
> And these re-sampled tiles are not going to be stored in the cache?
> I can understand that if this resampling is fast that that would make
> sense, but it would seem to me that at some point the disk IO would start
> to kill this not to mention the CPU load. Why would you not want to store
> these tiles or take a hybrid approach and save every 2nd or 4th level above
> the max as a compromise between storage and performance?
> Am I missing something obvious here?
> -Steve W
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