Chuck Jungmann wrote:
I am a new user of MapServer, using version 5.0.3 from the Ubuntu
repositories. I attempted to compile everything from source, had some
trouble, then decided to use the repository shortcut at least until I
understood how the application works.
I am writing an application where the browser requests a map by setting
the src attribute of an img object. Identifying locations on the
resulting map requires that the application knows the extent.
I calculate the extent of the map from various values, and use the same
algorithms on the server so the browser and the server agree on the
dimensions without having to negotiate. However, when I request the map
from MapServer, the extent of the resulting map is always larger (both x
and y dimensions) than what I requested, although still centered on the
same point.
Is this behavior normal (I don't want to beat my head against the wall
searching for an irrelevant math error)? Is there some setting that
might cause MapServer to more closely match my requested extent? Could
this be an error that was fixed in a more recent version of MapServer?
Any words of wisdom would be appreciated.
Chuck,
There are a number of conditions that may make mapserver checnge the
extents requested.
1) mapserver assumes square pixels, so if you ask for an extents that
has a different aspect ratio than that of you image size then mapserver
will make adjusts.
2) if you ask for extents and a scale, I think, mapserver will use the
extents to determine the center and then adjust the extents to the scale
Are you using the CGI interface? what does you request look like? You
need to give us more concrete examples that we can try here to test out
and explain what is happening. What version of mapserver are you using?
/path/to/mapserv -v
Will report how it was build with options and version number.
-Steve W.
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