[Mapserver-users] best way to color ramp topo/bathy data that'sin PostGIS

[Charlton Purvis]

Thanks for the help, Jan.  And I look forward to your presentation this
weekend.

I decided to go ahead and churn out a Perl script to generate the 256
classes for my .map file.  I provide it the starting color and the
ending color, and based on the max and min values of my layer, it
creates the expressions, etc.  (If anyone is interested, I'll eventually
post it.)

Yes, it does create a big .map file, but everything is modular and
automated.  And I seem to remember other folks w/ other automated .map
file generations.  So no matter what I do, large .map files may be hard
to avoid!

Anyway, let's say that I'm happy w/ plenty of expressions.  My question
is, am I compromising speed?  Having GRASS work w/ my rasters might
eventually be the way to go (as you suggest), but right now it sure is
convenient and clean to have everything in only one place, my PostGIS
db.

So am I losing any speed by choosing to let MapServer use expressions to
figure out what color to display rather than letting GRASS munch and
crunch it?  So far I am very happy w/ the MS performance (in general and
as it relates to this issue).  Of course, my dataset is very localized
and small at this point.

Thanks again.

Charlton

-----Original Message-----
From: Jan Hartmann [mailto:jhart at frw.uva.nl] 
Sent: Friday, May 30, 2003 6:05 AM
To: mapserver-users at lists.gis.umn.edu
Subject: Re: [Mapserver-users] best way to color ramp topo/bathy data
that'sin PostGIS

Hi Charlton,

I've been using GRASS/MapServer on a few 30sec global databases 
(elevation, satellite, landcover, going to show them on the User's 
Meeting). In my experience, putting everything in a GRASS database and 
displaying them directly from there in MapServer is the most efficient 
way. It's quick, lets you manipulate your rasters (e.g. colortables) in 
GRASS while immediately displaying them in MapServer, makes it 
incredibly easy to create tiles and tileindexes, etc. As to your other 
suggestions: I don't think PostGIS already has raster support, and the 
maximum number of classes in MapServer is 50 by default. You can compile

in a larger number, but you'll get horrible mapfiles.

Some time ago, Frank Warmerdam wrote about the possibility of color 
table processing in GDAL 
(http://mapserver.gis.umn.edu/data2/wilma/mapserver-users/0304/msg00621.
html). 
Is this something for a feature request? I think there are many people 
who could use such a feature.

Jan

Charlton Purvis wrote:
> Hi, folks:
> 
> I've got an approach question to ask.  I've been boning up on GRASS
and
> r.colors and MapServer integration.
> 
> Say I'm updating my PostGIS data based on :15 minute pings of netCDF
> DODS-available data.  In these datasets is some interpolated
bathymetry
> data.  What is the best way for me to store and then render it?
> 
> We're already going from netCDF to PostGIS.  I don't think I really
want
> to break my .map into a lot of classes (255?) to display a nice and
> gradual color ramp for different sea depths.  So should I be pumping
my
> PostGIS data into GRASS and somehow doing an r.colors on it to then be
> displayed by MS as a raster dataset?  Or should I be trying to take
> advantage of the alpha (?) GRASS version which already talks PostGIS
(I
> think I heard that somewhere)?  Or should I spend a little bit of time
> making a large .map file that contains many layers w/ unique RGB's?
> 
> Truth be told, I think the less pieces, the better.  I'd love to keep
it
> all wrapped up in MapServer.  But I'm trying to bone up on GDAL, too
> however, I don't quite see where that fits in.
> 
> Any help always appreciated.
> 
> Thanks.
> 
>  
>  
>  
> Charlton Purvis
> (803) 777-8858 : voice
> (803) 777-8833 : fax
> cpurvis at sc.edu
>  
> Advanced Solutions Group
> Department of Physics and Astronomy
> University of South Carolina
> Columbia, SC 29208
> 
> _______________________________________________
> Mapserver-users mailing list
> Mapserver-users at lists.gis.umn.edu
> http://lists.gis.umn.edu/mailman/listinfo/mapserver-users
> 

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