[gdal-dev] What options for display of high-quality ortho's via WMS?

[Martin Chapman]

Can you let me download the image you are having issues with?  You want to
have a pyramid of files that are varying levels.  Ideally they should be a
factor of 2, i.e
 2, 4, 8, 16, 32 , 64, 128, 256, 512, 1024, 2048, 4096, 
 .
What is the gsd of your base image?

 

Martin

 

From: Roger André [mailto:randre at gmail.com] 
Sent: Friday, May 02, 2008 2:54 PM
To: mchapman at texelinc.com
Cc: gdal-dev-bounces at lists.osgeo.org; gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] What options for display of high-quality ortho's via
WMS?

 

Well, generating overviews of the 8-bit data produced pretty awful looking
results.  gdaladdo did warn me, so I can't blame it.  ;)  Also changing the
resampling to bilinear did not improve the matter.

Is it better to create large, single-image overviews, or to create many
tiles of varying resolution levels?
--




On Thu, May 1, 2008 at 11:37 PM, <mchapman at texelinc.com> wrote:

Maybe try generating an overview
(.ovr) file for the image. Perhaps the resampling will be better. Also see
if you can specify in mapserver the resampling method to cubic convolution
or something other than nearest neighbor.

Martin


Sent via BlackBerry by AT&T


-----Original Message-----
From: "Roger André" <randre at gmail.com>

Date: Thu, 1 May 2008 21:20:04
To:gdal-dev at lists.osgeo.org <mailto:To%3Agdal-dev at lists.osgeo.org> 
Subject: [gdal-dev] What options for display of high-quality ortho's via
WMS?


Throwing out a general question to this list because I know that many of us
use a variety of different applications to "get the job done", but use the
GDAL tools as the common unifier (at least I like to think so).  I'm putting
together a Mapserver-driven web map that uses OpenLayers to get data via
WMS.  It's all working quite nicely, except for my aerial photo layer, which
I am not incredibly pleased with.  Despite using every tweak I could find
(convert from RGB to 8-bit with pct2rgb.py, use OUTPUTFORMAT with GD/PNG,
and use "DITHER=YES" in mapfile, I cannot get a very high quality rendition
of the photo layer in my WMS output.  It looks grainy in areas with solid
color and generally a bit "pixelly".  So I have a couple of questions.
 
1.  Is some loss of image quality an unavoidable side-effect of using
Mapserver?
 
2. If not 1, then are there other tweaks that can be done to further improve
the quality of my output?  (Note that I intend to use Tilecache, so maybe
slow initial performance may is an acceptable trade off, I dunno.)
 
3. If yes to 1, then what other open source tools do a better job of
rendering photo data?  (I intend to test some of the data in GeoServer, but
I haven't done so yet.)
 
Thanks in advance for your feedback.
 
Roger

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