[ka-Map-users] Vertically Stacked Data

David Bitner osgis.lists at gmail.com
Wed Jul 20 11:26:49 EDT 2005

I am trying to get a feel for what it would take to extend ka-map to
work with an idea I have or whether it would be easier to build from

The data that I deal with has some layers that draw incredibly fast
and create incredibly small images due to compression.  Other layers
(or groups) create much larger images or involve time filtered data
that would not be able to be cached and so would take longer to draw
since a new map would need to be created for any possible time choice.
 Currently I use a non-horizontally tiled interface that uses a
separate mapfile for each group and draws them as stacked pngs with
transparency.  The effect that this has is that when you pan (single
click, not drag) or zoom the fast layers show up almost instantly,
while the slower layers will build up the map with some time so you
watch the map build while getting some reference data right away, so
you could pan again before the slower data got there.

The next step to this approach would be to combine the set scales and
tiling that you are able to do with ka-map with the differences in
file size per a given tile size.  For example, one of my layers is
contours around an airport, another is a roads dataset for an entire
metropolitan area.  The contours are so small when compressed that you
could just have one image for each zoom level, meaning for that
particular layer, you would never have to do any railroading, it would
just be there.  The roads on the other hand would probably need to
tile at 200px on a side across the metro area.  Another group of
layers may be best tiled at 400px on a side.  From the way that you
have ka-map built, what I would like to see added to ka-map would be
the ability to use a different definition for each group (or separate
each group out as different maps) and have individual parameters for
tiling of each group including a bounding box outside of which there
is no data so no map request would even be made.

Does this seem feasible within the framework that you have set up?  If
so, what pointers might you have for getting started?

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