[OSGeo-Standards] Handling of resolution (or scale?) in WMSC

[Jody Garnett]

Christopher Schmidt wrote:
> "Scale" requires DPI assumption. "Resolution" does not.  
>   
You are correct; it seems that WMSC is reporting back the "resolution" 
of tile pixels to data units. However ... uDig allows users to set the 
scale of the current map (ie zoom in and zoom out). As such we would 
like to calculate the scale to zoom to in order to see a WMSC layer at 
one pixel 2 one pixel.  For WMS we are aware of how to do this since the 
rules by which it produces a pixel are well known.

I need to figure out something similar for WMSC.  I had a pretty good 
chat with Arne Kepp on IRC and he shares your opionion that this is not 
a reasonable request. But I am still left with the need - it looks like 
my best bet is to calculate a bounds to zoom to (as that will be easier 
than sorting out the scale...
>> My guess is the resolutions are calculated at the center of the tile set; 
>>     
> Huh?
>
> A dataset is a specific bounds: say, for example, -180,-90,180,90.
>
> The resolution is the description of the number of geographic units per pixel for a given tileset.
>
> 180 - (-180) = 360, / 256 -> 1.40625 (Default resolution for some things)
>
> I think the "global profile" for lon/lat says half of that: world in two
> tiles is .703125.
>
> But there is no need to consier 'at the center of a tileset' or anything else: the nummber of geographic units in a particular tile can't change, all the tiles are the same.
>   
Thanks for the clarification (it is what Arne Kepp also told me). Looks 
like I am going to have to modify how panning works in uDig (so we can 
pan with constant resolution rather than with constant scale). I will 
bring it up at tomorrows uDig meeting and what they think...

All the best,
Jody
PS. This conversation went much quicker