[ka-Map-users] Layer Interaction/Overlays

Sun May 29 21:28:06 EDT 2005

I don't think the concept is so difficult that it requires a third party 
library of code to handle it.

The question would be more of 'why do it'?  Opacity on layers is 
interesting, not so much from a user controlled point of view perhaps, 
but if it could be controlled through the map file (shouldn't be hard to 
add now)

Layer ordering on the client side doesn't seem like a very necessary 
thing to me, but it would also be easy to add to the kaMap API ... if 
someone can convince me that it is useful, or can provide the code

Cheers

Paul

arthur at sirius-cybernetics.info wrote:
> hi
> 
> maybe it's worth to have a look at http://dynapi.sourceforge.net/
> the DynLayer class seems to be suitable for all kinds of layer juggling...
> 
> Am 26.5.2005 schrieb "Moran Ben-David" <moran at place-base.com>:
> 
> 
>>Chris this is a great idea.  Especially in my line of work/applications
>>where we display thematic maps that don't allow even near complete caches of
>>maps or tiles.  Our work in http://www.dataplace.org
>><http://www.dataplace.org/>  (for fannie mae foundation - along with Vinq)
>>has relied on the simple
>>
>>
>>
>>1.       check tile cache
>>
>>2.       generate complete map (with thematic shading and layers)
>>
>>3.       slice tiles
>>
>>4.       cache tiles
>>
>>
>>
>>approach.  Our cache though currently large enough to have some recurring
>>cache hits, won't be able to be large enough for the future of our app.
>>That is we want to add more indicators to our system (and thus many more
>>potential maps being generated).  As well we want to add more complicated
>>maps and chart shields as labels.   The universe of maps even with Terabyte
>>drives won't be covered by pre-rendering.
>>
>>
>>
>>We have been aiming towards a client side rendering solution to increase our
>>cache hits.  I'm curious, has anyone tried rendering a map with
>>transparencies created by map server?   I.e. essentially doing what Chris
>>suggested?  Are the maps as pretty on Firefox (given that IE doesn't support
>>full alpha-channel usage in PNG's)?
>>
>>
>>
>>As well, has anyone looked at the approach of actually rendering the layers
>>(placing them on the map) one by one on the client?  I know this delves into
>>fattening the client beyond the abilities of javascript, but I'm curious if
>>this has been discussed in the ka-map group.
>>
>>
>>
>>Thanks,
>>
>>Moran Ben-David
>>
>>Placebase (www.place-base.com)
>>
>>
>>
>> _____
>>
>>From: ka-map-users-bounces at lists.maptools.org
>>[mailto:ka-map-users-bounces at lists.maptools.org] On Behalf Of Chris Tweedie
>>Sent: Tuesday, May 24, 2005 3:05 AM
>>To: ka-map-users at lists.maptools.org
>>Subject: [ka-Map-users] Layer Interaction/Overlays
>>
>>
>>
>>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 :-)
>>
>>
>>
>>---------------------------------------------------------------------------
>>
>>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:  <mailto:chris.tweedie at dli.wa.gov.au> chris.tweedie at dli.wa.gov.au
>>
>>Website:  <http://www.dli.wa.gov.au> www.dli.wa.gov.au
>>
>>---------------------------------------------------------------------------
>>
>>
>>
>>
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> 
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|Paul Spencer                           pspencer at dmsolutions.ca   |
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