[ka-Map-dev] Overlay Objects
lorenzo at ominiverdi.com
Wed Feb 8 06:10:40 EST 2006
Today I've started talking with Andrea about push a little bit on the
Next week we'll be together developing only on ka-map (maybe...)
Starting point is PG work:
His API seems to me a good starting point.
About Point, Symbol, Icon and Label implementation I've nothing to say
(maybe we can change little things before starting coding).
What we have in mind is about Linestring and Polygon. We want to start
from ka-map core function: tiling.
We hope to offer a solution that could work on any AJAX compliant
browser avoiding, for the moment, vectorial implementations as IE
Canvas or SVG or WZ_jsgraphics.
First of all we think to create a layer (we can call it Canvas, or a
better name) in the Viewport where, starting from XML, objects can be
designed by the server, then tiled and finally back to the client.
In contrary to wz_jsgraphics, this system permits managing Lines and
Polygons of big size and let us use pan and zoom functions without
charging the client (wz_graphics could really slow the client). For the
client is like another layer over the others: it can be very light if
well optimized (few kb for tile).
If there's an updating procedure we would like to try to implement a
solution that update only changed tiles (es: a point that moves on the
now the problem is to give this drawn objects some life.
We think to create a "special" level (trying to call it CanvasProxy, or
a better name).
We are not sure about this implementation, maybe somebody can
contribute with a better idea.
Anyway we want to use, inside the CanvasProxy, a transparent image (1px
height & width) and force his dimensions to the map extent (so it
changes depending on zoom level) then let it pan as layers below.
The hazard is: an imagemap.
Imagemap is the only HTML object that permits to design irregular
polygons (not just rectangles) and simply attach event listeners (es:
onclick, onmouseover). Moreover it can be easily manage with DOM
scripting (+ or -).
Now, for each polygon drawn in the Canvas there will be an AREA tag
with his shape (rectangle, circ, circle, poly, polygon; maybe just
polygons) for the CanvasProxy transparent image. Then for each polygon
we can associate onclick and mouseover events extending ka-map ones.
In a future we can extend this method to edit objects just drugging
polygon extremes, alter the XML on the fly and send it back to the
server to render the Canvas layer.
To start working on this we need to choose the XML schema we want to
use. Maybe Paul already decided (let us know).
please, send comments
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