[mapserver-users] ScaleHint (again)

[Stephen Lime]

Well, MapServer treats lat/lon as a planar coordinate system for the most part. That's expected. To calculate a scale you need a conversion between decimal degrees and a known unit (i.e. inches). Problem with longitudes is they are not fixed and as you move north... blah, blah, blah. The internal code uses a dd to inches value that is valid at the equator, which may explain the goofiness you're seeing espcially if you're working a ways north. It's an arbitrary decision, but since there's preopably no good value and scale makes no sense with lat/lon for the most part I haven't worried about it. Perhaps it should be tunable.

Steve

Stephen Lime
Internet Applications Analyst

Minnesota DNR
500 Lafayette Road
St. Paul, MN 55155
651-297-2937
>>> Paul Ramsey <pramsey at refractions.net> 09/07/01 18:16 PM >>>

How does the WMS ScaleHint behave in the presence of projections? I have
a WMS service where the data is all in a planar projection. Browsing in
the planar projection using good old mapserver interfaces, everything is
hunky dory. Browsing in lat/lon, things go off the rails. I can request
potentially debilitating quantities of data from the server, and it'll
try and render *all* of it. I am quite ignorant of the voodoo behind
min/max scale and how thing kind of thing would behave with respect to
reprojection, particularly into something completely off the wall like
lat/lon.

Paul

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     | Paul Ramsey
     | Refractions Research
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