negative values and colors in Ascii Grids

[Christopher Condit]

Hi Frank-
I'm also very interested in this topic and have been trying to
efficiently create raster images from continuous oracle point sources.
Currently, I write the Oracle points to a ArcInfo ASCII grid and create
all of my own CLASS directives for MapServer.  Do you know of a better
way to do this?  Problem is: I need the raster to come from a DB query
input by the user, so I can't create static images ahead of time...

Thanks!

Chris

-----Original Message-----
From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of Frank Warmerdam
Sent: Monday, January 16, 2006 12:03 PM
To: MAPSERVER-USERS at LISTS.UMN.EDU
Subject: Re: [UMN_MAPSERVER-USERS] negative values and colors in Ascii
Grids

On 1/16/06, Carola Jesch <cjesch at cct.lsu.edu> wrote:
> Hi Frank,
> I had a look to the raster-howto and the sources as well, but was
unsure,
> because I can't imagine that most users have grids that exactly have
values
> between 0 and 255 in it.

Carola,

Well, most folks are working with simple 8bit images where
scaling is not required.

> So sorry fot the questions.
> Do you plan to implement a colormap for ascii grids like the clr for
binary
> grids?

I wasn't planning to do so, but it looks like it wouldn't be too hard.
Note that ASCII grids are a terrible format to run mapserver from
due to the amount of processing required when reading it.

> What would you suggest to display the negative values?

If you want detailed control of the colors then create a series of
classes.  If a greyscale is fine then just use automatic or
explicit scaling values.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent