Status: Layer organisation

[Martin Schulze]

Hi,

since it is now possible to select which layer the WMS server should
render for Thuban, it starts to make sense to mix WMS resources with
local resources or with other WMS resources.  For example, it could be
easier and faster for hide some layers and re-display them later.

However, this does require transparent layers which can be stacked.

In trying this, it seems that I have opened a can of worms:

 1. Transparency is not supported by JPEG, but only by PNG (through an
    alpha channel), GIF and probably BMP.

 2. The internal render engine from Thuban does only support BMP and
    JPEG at the moment.  At least on GNU/Linux it is no problem to
    support PNG, TIFF and GIF as well.  See [1].

 3. The frida server only supports JPEG, PNG, GIF and WBMP.  WBMP is
    Wap Bitmap, something you may find useful on your mobile phone but
    not on a standalone computer.

 4. At least the frida server supports transparent PNG and transparent
    GIF images.  See [2] as an example.

 5. Even after I added support for PNG and GIF (see [1]) the results
    were not promising since the transparent background was rendered
    in a bright pink tone (#FF00FF), a nice colour but not exactly
    suited for transparency.

As a result of 1 and 2 the CVS version of Thuban does not support
transparent image layers.  Bummer.

As a result of 1, 2 and 3 it is not possible with the CVS version of
Thuban to use more than one layer of frida.

As a result of 5 it is currently not posible to use multiple image or
WMS layers with Thuban.

I had hoped that transparent images would be supported since that
would have delivered such a nice presentation tomorrow (I need to give
a talk about WMS to members of the environmental computer science).

Todo:

 1. I guess that we should see if we can support more graphics
    formats.  That's easily doable, but there may be a good reason for
    limiting support to BMP and JPEG.

 2. If 1. we should see why transparency is currently not supported by
    Thuban and see if we can fix this.


Links:

 1. http://intevation.de/pipermail/thuban-devel/2004-April/000094.html

 2. http://frida.intevation.org/cgi-bin/frida_wms?LAYERS=Osnabrueck&STYLES=&SERVICE=WMS&SRS=EPSG%3A31493&FORMAT=image%2Fpng&REQUEST=GetMap&HEIGHT=600&WIDTH=800&VERSION=1.1&BBOX=3426792.643114%2C5786721.353642%2C3444358.076702%2C5801282.173590&TRANSPARENT=TRUE

Regards,

	Joey

-- 
It's time to close the windows.