[ka-Map-users] Layer Interaction/Overlays

[Chris Tweedie]

To Paul / rest of the devs, what's your thoughts on adding transparency
to the tiles and allowing tile/layer overlays? I see you have commented
out the following, so you may be already looking at this?

 

        // TODO: We don't need transparency for now

        //$oMap->outputformat->set("transparent", MS_ON );

 

Im looking at instead of creating the tiled images based on all layers
in the map file, I would add a new config switch to specify particular
layers that you wish to split into separate tiles. Ideally, this would
allow particular layers in the map to be toggled on/off and be moved
hierarchically all on the client side.

 

Advantages:

-          Complete client side transparency / z-index position using
CSS / DOM / JS

-          Same benefits with cached tiles but further functionality

-          Remove reliance on the server regenerating images to perform
simple layer ordering functions

-          Will suit the planned cache refresh function seen on
bugzilla. If a layer data source is updated, only related layer images
need to be flushed, not everything.

 

Disadvantages:

-          Cross browser support issues

-          Integration with current code would require directory and
tile algorithm change

-          Annotation clashes due to the images being created
independently. ie. labels and symbols may become illegible

-          Increased overhead downloading images

 

While the download overhead may be significant depending on the number
of images you wish to overlay, typically you'd limit the amount of
layers available to be moved/turned off. However as the xmlhttprequest
handles concurrent downloading of images, I'd expect most users will not
notice the increased data as they can continue to zoom/pan.

 

Thoughts/Opinions? Thought I'd throw the idea out there and gauge a
response. Afterall, no point reinventing the wheel :-)

 

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Chris Tweedie

Technical Officer

Shared Land Services

Department of Land Information

1 Midland Square, Midland, Western Australia 6056

PO Box 2222 Midland 6936

Telephone: (08) 9273 7520 Facsimile (08) 9273 7638

Email: chris.tweedie at dli.wa.gov.au <mailto:chris.tweedie at dli.wa.gov.au> 

Website: www.dli.wa.gov.au <http://www.dli.wa.gov.au> 

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