[OpenLayers-Users] WMS without bounding box/ViaMichelin

[jonz]

Hi,

We've set up an interface to the ViaMichelin mapping service (they provide
webservices which we have mapped to  simple http calls accessible via web. 
I've used the WMS untiled.js layer to implement the interface. 
The main problem is that to generate a map with ViaMichelin, you must
specify the geo coordinates (WGS84) of the center point, dimensions in
pixels of the map being generated, and the "pixelsize", the size of a single
pixel in meters.

Unfortunately this does not seem to lend itself to OpenLayers as far as I
can discern. In any manner you try to approximate the pixel size in meters
from the resolution, it will never work out precisely enough. 
The result is other than not being able to accurately put POI's on the map,
map movements, even on an untiled map are not perfect as the real
coordinates of the map as perceived by Michelin are different than
openlayers. 
Our application is very local, only Italy, so it's too some advantage. But
in any case, any approximation to pixel size can never be correct as I can't
imagine how a pixel can be "square", when measured in meters but using geo
coordinates for positioning, e.g. 1 degree in latitude in meters in europe
is not quite the same as a degree of longitude in meters.

They do not have a "bounding box" type implementation. The only other thing
that is retrievable are the pixel coordinates for any geographical
coordinate on the map. I was working with a tile of 800x800 and so after
loading the tile, I generated the lonlat for the upperleft and lowerright
corners, hopefully trying to "reset" the openlayers extent to these,
correcting the openlayers value, but I saw that this is not too simple, as
the extent is continuously calculated based on the center and resolution on
every move.

Any ideas?

TIA
Jon Zaid

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