todd runstein a écrit :
Suppose I'm using EPSG:4326, and I have the two
coordinates -122:40 and -120:42. It would seem
reasonable that because -122-(-120)=-2 and 40-(42)=-2,
I have a proper square (something that would fit
nicely in a 500px X 500px window). Following this
logic, -122:40 and -120:43 would fit in a 500px X
750px window.
It would appears as a square if two conditions are meet:
* The underlying coordinate system is cartesian.
* All axis use the same units of measure.
Those conditions are often true for a projected CRS. But EPSG:4326 is a
geographic ones, and all geographic CRS use an ellipsoidal CRS. Whatever
such shape in a geographic CRS appears like a square or not is renderer
dependent. It depends if the renderer performs on-the-fly reprojection
in order to take in account the flat shape of the screen, or if it just
display the shape "as is" without any processing. In the later case the
shape will appears as a square, but you should generally not rely on that.
Note that for any computation of geometric properties like distance,
area, angle, etc., you should definitively not assume that the shape is
square and not rely on euclidian formulas for geographic CRS.
Martin.
-------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
for problems? Stop! Download the new AJAX search engine that makes
searching your log files as easy as surfing the web. DOWNLOAD SPLUNK!
http://ads.osdn.com/?ad_idv37&alloc_id865&op=click
_______________________________________________
Geotools-gt2-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
