[OpenLayers-Users] tilecache config problem]

[Christopher Schmidt]

On Wed, Jan 10, 2007 at 12:02:51AM +0100, Andrea Borruso wrote:
> Christopher Schmidt ha scritto:
>> The default resolutions array, if one is not specified, assumes a top
>> level resolution of:
>> 
>> res = largerMapDimension (geographic) / 512 
>> 
>> With a default bounding box of -180,-90,180,90, for example, the default
>> max resolution is .703125. Beyond that, each layer is divided by 2, so
>> the next layer down is .35106125, etc.

> Why you say that the default max resolution is .703125? This one should
> be the smallest. Am I wrong?<br>

This is the *largest* resolution, but the smallest number of pixels in
the map. (It is the 'smallest' scale: 1:250Million ish.) As you zoom in,
the resolution gets smaller, and the scale gets larger.

> When you say geographic units, you say degrees or the units of the map
> I'm using?<br>

The units of the map you're using.

>> The default OpenLayers setup is to go from 80 (80m/pixel) to 40m/pixel,
>> 20m/pixel, etc. so:
>> 
>> 80,40,20,10,5,2.5,1.25,0.6125

> There is something I do not understand. The original resolution of my
> raster map is 80 meters (1 pixel = 1600 square meters). It's the max
> resolution, then I thought to have this array of resolutions:<br>
> 1280,640,320,160,80. Am I wrong?

I may be confused in some way, but it sounds like you're describing the
*minimum* resolution of the map. So yes, You're right, and you should
configure OpenLayers that way.

Since I seldom have source map data, I'm not used to the description
you're using, but it sounds like you're right. Of course, you could have
a lower resolution than 80m/pixel if you chose -- you just would start
to see visual effects at some point. I've displayed images at 200 times
their original resolution and found them useful in the past.  

-- 
Christopher Schmidt
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