[Tilecache] Help with resolution setup..

[Christopher Schmidt]

On Tue, Jan 08, 2008 at 11:59:23AM -0500, Mark Deneen wrote:
> I am trying to figure out what units "resolution" is in.  I am using the 
> following config:
> 
> [basic]
> type=WMS
> url=http://this.is.internal.only.but.it.is.a.geoserver.wms.handler/
> layers=basic
> extension=png
> metaTile=true
> size=256,256
> srs=EPSG:4326
> resolutions=0.1
> bbox=-180.0,-90.0,180.0,90.0
> 
> Let me preface this by saying that I am fairly new at GIS and 
> cartography. With that being said....
> 
> I would like to think that 0.1 means 36 degrees / 360 (from my bbox) = 
> 0.1.  This should make the world (in EPSG:4326) 50 tiles, 10 east/west 
> columns of  5 north/south rows. Obviously, since I am writing this 
> email, this isn't working for me.  I am using world wind requests and at 
> resolution 0.1, I end up with 6 tiles N/S and 13 E/W.  I really want to 
> understand what resolution is, and how I can calculate it.  Currently, I 
> want to dice the map up into 36 degree squares for testing.
> 
> Can someone shed some light on what resolution is, or where I can read 
> more about it?

Resolution is units per *pixel*, rather than per tile: you probably want
something like .140625 (36 degrees / 256) to get 36 degree squares. 

Also, TileCache can spit out WorldWind XML metadata which you can load
directly -- let me know if you can't figure out how to make that happen. 

Regards,
-- 
Christopher Schmidt
MetaCarta