Dumb question on Extents

[imap at chesapeake.net]

CS,

The "units" describes the map coordinate system.  It could be meters, feet or
degrees for non-projected data.  A given shapefile has extents, which can
be extracted and viewed with a command-line program called "shpdump" which
can be found in <ms_3.2>/shapelib.  There are a couple of utilities in that
directory... well work the time to check them out. 

Logfile entries are modelled after the httpd stuff (sort of), and sometimes
can be your only source of debugging. 
<time> <pid> <remote_addr> <map_name> <extents> <map.x> <map.y> <layers>
<status>

When something goes wrong, make sure to check the status field.  On the first
map
being blank make sure passing at a minimum the following:

&map=<mapfile>
&mapext=<minx>+<miny>+<maxx>+<maxy>      (the "+" is a literal seperator)
&zoomsize=<value>


My test URL looks like:

http://localhost/cgi-bin/mapserv.exe?map=test.map&mapext=-3300000+3000000+3220000+6300000&zoomsize=2&mode=map

produces a map only....  

As far as debugging things, make sure you check your httpd error_log and the
mapserver 
access_log.   Usually you get some thin message from mapserv, but depending on
the
severity you may not get anything... In which case, check the logfiles.  That
should
give you a clue about what is broken.  With respect to debugging, the error
messages
are terse.  Steve improved this area to some degree, but we still needs more
verbose
msError.message ;)

Since I was up early this morning, I thought I would go ahead and answer what
I could.

Regards,

-Chris (imap at chesapeake.net)


Cameron Shorter wrote:
> 
> Hi,
> 
> I'm having problems getting my first map to come up.  So far all I'm
> getting is a blank page, which raises the following questions.  (Please
> excuse me, but I have no GIS training).
> 
> * What are the units of Map Extents, and what are they relative to?
> 
> * Given a shapefile, how do I determine the Extent of the data represented
> in it?  I've tried working this out with ArcExplorer, but I'm stumbling
> over units.  Hence the previous question.
> 
> * It would be good if there was an explanation of what the fields in the
> logs mean (although I think I've guessed most of the fields).
> 
> * Are there any other debugging tools around that I should know about?
> 
> Cameron Shorter
> 61.2.9901-1596 work.