[mapserver-users] CGI mapserv.exe - BUFFER

[Donald Kerr]

Christopher,

Your email came in just as I posted a thought on my original posting. I said
that "I wonder if the BUFFER is actually a
buffer to both sides of the XY specified in "MAPXY"!

You've confirmed that I was nearly right! If it's a radius and the width of
the image is greater than the height then the width in metres is indeed
twice what is specified in BUFFER.

Many thanks indeed.

Regards,

Donald

-----Original Message-----
From: Christopher Schmidt [mailto:crschmidt at metacarta.com] 
Sent: 08 January 2009 19:24
To: Donald Kerr
Cc: mapserver-users at lists.osgeo.org
Subject: Re: [mapserver-users] CGI mapserv.exe - BUFFER


On Thu, Jan 08, 2009 at 05:47:09PM -0000, Donald Kerr wrote:
> I'd appreciate it if someone could give me some clarification please?
> 
> I am using the following url to return an image:
> 
>
http://localhost/cgi-bin/mapserv.exe?map=/ms4w/os.map&mode=map&mapsize=500+4
> 00&mapxy=258544+665909&layers=all&buffer=2000
> 
> The documentation states, "BUFFER [distance] - A distance, in the same
> coordinate system as the map file, used in conjunction with MAPXY to
create
> an new map extent".
> 
> The coordinate system is in metres so I would expect that the width of the
> image (500px) would be 2000m (2km). That doesn't seem to be the case i.e.
> the returned images is, at a guess, double that.

"Buffer" is usually a 'radius' -- so, you've got 2000M on each side (4k
total, instead of the 2k you expect).

If you imagine picking the center piont, and drawing a $buffer_size
circle around it -- that's your extent.

Regards,
-- 
Christopher Schmidt
MetaCarta