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

Stephen Woodbridge woodbri at swoodbridge.com
Tue Apr 16 06:36:30 PDT 2013

On 4/16/2013 2:43 AM, thomas bonfort wrote:
> Devs,
> Please find RFC97:
> 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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