[Chameleon] How to specify 24bit output for a WMS layer within
an xml context file?
Jeff McKenna
jmckenna at dmsolutions.ca
Tue Jan 24 08:23:49 EST 2006
Have you tried setting Chameleon's "image_type" parameter to PNG24 in
/config/chameleon.xml?
jeff
Jennifer Zeisloft wrote:
> Hello All,
>
> I have been having problems displaying raster imagery from web mapping
> services in MapServer/Chameleon (poor visual resolution, essentially).
> I first sought help from the MapServer list (pasted below), but have
> discovered that I likely need Chameleon help.
>
> Specifically, I am wondering how I can specify that 24bit output be
> generated from a layer in a web mapping context.
>
> In addition to the responses below, Frank Warmerdam also suggested
> adding PROCESSING "DITHER=YES" to the mapfile if I do not specify jpeg
> or png24 in the mapfile output. This did help somewhat. But again, the
> problem is that I cannot refer to a mapfile in an xml context file (as
> far as I know). So, there must be some other means in Chameleon of
> specifying that the output is 24bit rather than 8bit.
>
> I am grateful for any hints or ideas you can offer!
>
> Thanks!
>
> Jennifer Zeisloft
> UW Sea Grant
>
> ------------------------------------------------------------------------------------------------------------------
> >From the MapServer List Discussion:
>
> Greetings All,
>
> We have been noticing that some (but not all) WMS raster images look
> pretty terrible (extremely low resolution compared to what they should
> be) when added to our MapServer application. For instance, from
> TerraServer (http://terraservice.net/ogcmap.ashx), USGS Digital Ortho
> Quads are virtually useless regardless of scale, while USGS DRGs look
> decent. Daily MODIS imagery from NASA JPL World Map Service
> (http://wms.jpl.nasa.gov/wms.cgi?) has also typically been a problem.
> And there are others...
>
> I have recently been playing with GDAL to display our own rasters, but
> also partially with the hope that it might somehow magically fix this
> problem (of course it hasn't).
>
> I am wondering whether the display problem is local or if it is on the
> data custodian's end, and whether this is typically the case. Is there
> any way to correct it? If it is at the custodial end, what might be
> done differently to increase the display resolution for WMS clients (so
> that we don't make the same mistake)?
>
> I really appreciate any hints or ideas you can offer.
>
> Thanks much!
>
> Jennifer Zeisloft
> UW Sea Grant
>
> ------------------------
> Jennifer -
>
> You don't give us much information to go on, other than your dislike of
> the results!
>
> If you're consistently seeing poor-quality results, then there may well
> be something systematic you're doing in your map files or MapServer
> configuration. I'm assuming you're using MapServer to generate these
> "horrible-looking" images. If you are, for example, requesting
> low-color output from high-color images, you're going to see blotchy
> output. DRGs are low-color images (only 13 unique colors) so they are
> not as prone to being affected by a low-color output request.
>
> Could you provide an example of the map file and configuration you're
> using to retrieve and display these images? There's nothing special
> about the WMS interface that inherently limits image quality - you can
> get a perfect reproduction of the source imagery in many cases.
>
> - Ed
>
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com / Maps a la carte, Inc.
> 73 Princeton Street, Suite 305
> North Chelmsford, MA 01863
> Phone: +1 (978) 251-4242
> Fax: +1 (978) 251-1396
> ed at topozone.com <mailto:ed at topozone.com>
>
> --------------------------------------
> Thank you for responding, Ed.
>
> Actually, these raster data sets are displayed as part of Chameleon
> contexts (so there is no mapfile). I added the USGS orthos to a mapfile
> to see if the result was any different and it wasn't (the mapfile code
> for this layer is pasted below in any case).
>
> The application can be found at
> http://maps.aqua.wisc.edu/lscmp/viewmaps.phtml. The example data sets I
> am referring to can be found in the Wisconsin: Imagery context.
>
> I have read through the documentation on rasters in MapServer, as well
> as searched list archives and have not been able to determine how I
> would go about specifying low or high -color output. So, perhaps this
> is part of the problem?
>
> Again, any suggestions are greatly appreciated!!
>
> Jennifer Zeisloft
>
> LAYER
> NAME DOQ
> STATUS ON
> CONNECTIONTYPE WMS
> TYPE RASTER
> CONNECTION "http://terraservice.net/ogcmap.ashx"
> PROJECTION
> "init=epsg:4326"
> END # Projection
> METADATA
> "wms_srs" "EPSG:4326"
> "wms_name" "DOQ"
> "wms_title" "USGS Digital Ortho-Quadrangles"
> "wms_onlineresource" "http://terraservice.net/ogcmap.ashx"
> "wms_abstract" "NA - test"
> "wms_keywordlist" "NA -test"
> "wms_server_version" "1.1.1"
> "wms_formatlist" "image/png,image/jpeg,image/wbmp"
> "wms_format" "image/png"
> END # Metadata
> END # layer
>
> -------------------------------------
> From: Frank Warmerdam <warmerdam at pobox.com
> <mailto:warmerdam at pobox.com>> Mailed-By: lists.umn.edu
> <http://lists.umn.edu>
> Reply-To: Frank Warmerdam <warmerdam at pobox.com <mailto:warmerdam at pobox.com>>
> To: MAPSERVER-USERS at lists.umn.edu <mailto:MAPSERVER-USERS at lists.umn.edu>
> Date: Jan 23, 2006 10:57 PM
> Subject: Re: [UMN_MAPSERVER-USERS] Horrible Looking WMS Raster Imagery
>
> On 1/23/06, Brent Pedersen <bpederse at nature.berkeley.edu
> <mailto:bpederse at nature.berkeley.edu>> wrote:
> > have you tried using image/jpeg?
>
> In addition to fetching data from the remote WMSes as
> JPEG, it is also necessary for mapserver to generate 24bit
> output (JPEG or PNG24 for instance). I don't know how to
> do that with Chameleon myself, but I'm sure there is a setting
> somewhere.
>
> I think Ed is right that the problem is 24bit to 8bit color
> conversion with correspondingly poor color resolution.
> Given sufficient blotchiness from this conversion it can
> even appear that spatial resolution is degraded (though it
> isn't actually).
>
> Best regards,
> ---
>
> I set the clouds in motion - turn up | Frank Warmerdam,
> warmerdam at pobox.com <mailto: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
>
> ------------------------------------------------
> Brent,
>
> Thanks for the suggestion. I switched the output from png to jpeg - but
> no change (the jpeg might have looked a little worse??). Still, the
> crux of the matter is, I suppose, that these images are displayed
> through a context file. The rasters are coming straight from their
> "original" (perhaps) source, which doesn't allow me to specify how the
> image is displayed, but merely that an image is displayed (furthermore,
> the context file is automatically generated by the "Save Context" widget
> in Chameleon).
>
> And an addendum to my last message: I did find output specifications in
> the documentation
> (http://mapserver.gis.umn.edu/docs/reference/mapfile/outputformat/), but
> I don't have the opportunity in this instance to specify the output in
> this sense.
>
> Jennifer
>
> -----------------------------------------------
> Hi Frank,
>
> Thanks for the response, Frank. It is sounding more and more like this
> is a question I ought to forward to the chameleon list - because I am
> also not sure how to generate 24bit output with chameleon!
>
> I appreciate the much needed direction!
>
> Thanks all!
>
> Jennifer
>
--
Jeff McKenna
DM Solutions Group Inc.
http://www.dmsolutions.ca
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