[ka-Map-users] Layer Interaction/Overlays

Fri May 27 08:58:08 EDT 2005

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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