[mapserver-users] pre-projection

[Ed McNierney]

Brian -

As long as it doesn't interfere with the management of your data,
pre-projecting your source data into your output projection makes a lot
of sense.  However, if your goal is to make (perceptible) performance
improvements in your application, I'm not sure this will help much.  The
PROJ library support in MapServer is VERY fast in my experience, and
I've been quite surprised at how small the impact of reprojecting
point/line/polygon layers is.

Reprojection is just a bunch of in-memory math, which computers do
really quickly.  The really slow stuff is looking for and reading data
from disk, and if you're looking for performance improvements the first
thing I'd do is make sure my data is organized and indexed so each map
request has to touch the absolute minimum amount of data it doesn't
need.  If pre-projecting the data DOES make a noticeable difference,
that might be evidence that your data isn't well-structured to begin
with.

	- Ed

Ed McNierney
Chief Mapmaker
TopoZone.com
ed at topozone.com
(978) 251-4242


-----Original Message-----
From: Brian Hill [mailto:bhill at nextbus.com]
Sent: Wednesday, October 31, 2001 5:41 PM
To: mapserver-users at lists.gis.umn.edu
Subject: [mapserver-users] pre-projection


I have tiger data in geographic projection, and other data in a mercator

projection.  My output projection is the mercator projection.  All the 
preceding is specified in my .map file.

Does one of the MapServer utilities allow me to pre-project all the 
tiger data into the same mercator projection so that the transformation 
doesn't have to be done on-the-fly?  If so, are there directions 
somewhere (something much more detailed than the discussion at 
http://mapserver.gis.umn.edu/coordinates.html ) that I can follow to do 
this operation?

My goal is to make my installation perform better, and I am hoping from 
previous posts to this list that this will be the ticket.  Thanks very 
much for any pointers. --Brian Hill