[mapserver-users] Creating lower aeriel image cache from the best resolution tiles

[Rahkonen Jukka]

Hi,

You do not need to be stupid and make MapCache to use it for everything :)

I bet you have used gdaladdo sometime in your life. I have a feeling that Maptiler is also working in this order so there is nothing new in the idea. And if you ask the tile for level Z0 of an aerial image layer for the first time from WMS server you actually ask the server to downsample the full coverage from the native resolution images. Of coarse we, the server admins, have done something to prevent such a lunatic thing to happen and we have overviews in the images and we use generalized layers in scale dependent layer groups. But at least  our Mapserver is still  rather slow when the BBOX is large.

You can make a test which is basically doing the same thing as
gdalwarp -of GTiff a_tile.tif b_tile.tif c_tile.tif d_tile.tif -tr [double the original] next_level_tile.tif

I bet you know some programming tricks for making that very fast with multithreading and everything. If it is fast then there is some advantege, if not, we can forget the idea.

-Jukka Rahkonen-

________________________________
thomas bonfort wrote:

> Jukka,
> No this is not considered, and you'll have to be really persuasive to make this happen as I do not see any advantage of adding this :) The reason is that in order to create e.g. the tile for level 0 for the first time, you'll have to downsample (and maybe previously seed) the full z=21 level (and all the intermediate ones).

> regards,
> thomas


On 9 June 2013 18:02, Rahkonen Jukka <jukka.rahkonen at mmmtike.fi<mailto:jukka.rahkonen at mmmtike.fi>> wrote:
Hi,

Have you been considering to seed the cache for aerial or satellite image layers in opposite order compered to the normal Z0, Z1, Z2... so that only the best resolution Z(max) tiles (or perhaps also Z(max-1) were requested from the WMS? The lower resolution tiles could me created by combining and resamplint tiles from the tiles of the higher zoom level in groups of 4. This should be much faster than asking lower level images from the WMS, especially if the WMS is a remote one and connection is slow. If resampling from Z+1 tiles yields to artifacts I feel that quality by resampling from Z+2 would normally be good and speed migh be still fantastic.

-Jukka Rahkonen-

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