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

[thomas bonfort]

Passed with +1 from ThomasB, StephanM, MikeS, TomK, JeffM, DanielM,
PerryN and SteveW

On 16 April 2013 16:51, Stephen Woodbridge <woodbri at swoodbridge.com> wrote:
> +1 great idea.
>
> Duh! Told you I hadn't had enough coffee, got up and down flipped in my
> head.
>
> Thanks,
>   -Steve
>
>
> On 4/16/2013 9:43 AM, thomas bonfort wrote:
>>
>> Steve,
>> 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 ?
>>
>> --
>> thomas
>>
>>
>> On 16 April 2013 15:36, Stephen Woodbridge <woodbri at swoodbridge.com
>> <mailto: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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>>
>