Many thanks for your helpful response Simone, much appreciated. I am now using an ImageMosaic source which was very easy to do, and as you say it supports setting of the transparent colour for my MrSid images which works great.
One thing I did notice is that it can be slower to generate tile images when using ImageMosaic when compared to using a Layer Group for the same set of images. It only seems to be slower though when the requested tiles cover an area which requires imagery from more than one of the source images. By way of example, requesting 35 tiles at TMS zoom level 19, all coming from a single source image, took 5 seconds to serve on my platform with both the ImageMosaic and Layer Group approaches, but requesting 35 tiles at zoom level 15, which in this case requires parts from 3 of the source images, takes 65 seconds using ImageMosaic but only 16 seconds using a LayerGroup.
I realise the ImageMosaic would have to do some extra work to take the transparent colour into account at the image borders, so to check this I tried deleting the InputTansparentColor for the ImageMosaic. This speeded things up from 65 seconds to 37 seconds, but this is still less than half the speed of the layer group. I guess the ImageMosaic must also be doing something extra that the layer group is not.
As you suggested, I filed a JIRA request for an enhancement for layer groups to support setting of a transparent colour at https://jira.codehaus.org/browse/GEOS-5501.
Regards
Tim
-----Original Message-----
From: Simone Giannecchini [mailto:simone.giannecchini@anonymised.com]
Sent: 01 December 2012 09:08
To: Tim Hayton
Cc: geoserver-users@lists.sourceforge.net
Subject: Re: [Geoserver-users] How to set InputTransparentColor for MrSid layers?
Ciao Tim,
please, find my aswer inline below....
Regards,
Simone Giannecchini
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On Wed, Nov 28, 2012 at 4:08 PM, Tim Hayton <tim.hayton@anonymised.com> wrote:
I've just started using GeoServer/GeoWebCache to serve map imagery to
web clients which use the TMS service. My source images are in either
GeoTIFF or MrSid format, and are satellite imagery for adjacent areas
which slightly overlap. I have successfully set these up in GeoServer
as data sources and layers, and then made a Layer Group which combines
each individual image layer into a single group so I can easily get
tiles for anywhere in the coverage area via a single TMS request.
I would suggest to use the ImageMosaic plugin.
I am assuming the images have:
- same CRS
- same data type
- same number of bands
- similar resolution
With the ImageMosaic plugin you do not need to use the layer group and your GetCapabilities will be much smaller.
ImageMosaic handle the transparent color both on put images as well as on the output image. Check the layer configuration.
Last but not least it does handle MrSID as well as GeoTiff files.
My problem is related to nodata areas, which are black in the
individual images, at the borders of each image file where there is an
overlap with the next image. For the GeoTIFF layers, I can easily set
the InputTransparentColor in the GeoServer Layers -> Coverage
Parameters screen, and this works great with the combined layer group
correctly serving the actual data rather than the black pixels for tiles where two images overlap.
However, for my MrSid images, there is no InputTransparentColor option
in the Layers screen, and when I get border tiles with TMS requests I
am often getting the black pixels in preference to the actual data
where tiles overlap.
See suggestion above about using ImageMosaic. That said you are right there is no support for input transparent color on GDAL Formats. Could file a jira enhancement report for this?
It would be dead easy to add it and I believe we should do it right away.
So my question is basically is there any way to set the
InputTransparentColor for layers based on MrSid data sources, or is
there something peculiar to this format that prevent this option from being set?I also see the same problem if I get a tile layer preview from the web
interface, but interestingly if I ask for a layer preview (rather than
a tile layer preview) the I do not see the problem, and the image
layers blend correctly at the borders. I wonder then if the problem
might be related to the way GeoWebCache requests the images from
GeoServer in a way that causes the nodata to take preference somehow?System details:
GeoServer 2.2.2 from windows installer
GDAL extensions
Windows XP
Oracle Java 1.7.0_09
Thanks in advance for any help!
Tim
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