Hi Sam,
There are different vector rendering technologies: SVG, VML, Canvas,
Flash, Silverlight, PDF, etc. As far as I know, OL supports SVG, VML and
canvas. Depending on the browsers it will decide which technology it
will use: IE6 to IE8 will render with VML, all other browsers, including
IE9 will render in SVG by default. But you can override settings, e.g.
if you wish to rencer in canvas.
In the future, VML will disappear and there will be mainly SVG and
Canvas. Those two are quite different. SVG is based on a DOM tree and
keeps it state, while canvas renders vectors into rasters and then
forgets about its state. Canvas is often faster, but not very suitable
for interactive vector graphics, this means if you want to edit or
restyle features without reloading/redrawing, you are better off with
SVG. SVG performance also improves from browser to browser.
As to performance problems: especially with IE6 to IE8 you will
certainly run into performance problems. Other browsers should be much
better. However, there is a limit as SVG is a DOM based technology. This
limit depends on hardware and software and could be with several
thousand features or even below. If you have tens of thousand of
features you definitely need a different strategy. One strategy would be
to render in raster unless you need special interactivity or editing.
You would enable editing only at certain zoom factors, which means that
you would have a lot less features in the DOM.
Hope this helps a bit,
Andreas
On Wed, 25 May 2011 17:05:08 -0600, Samuel M. Smith wrote:
How does Openlayers render features on a vectory layer? How are they
represented internally. From my limited understanding of Javascript,
there are no graphics primitives for drawing arbitrary shapes. HTML5
has a canvas element that allows such graphics primitives but
OpenLayers
doesn't require HTML5 so I am curious how its done?
Also if I want to display a lot of geometry on vector layers will I
run into performance problems with the javascript based rendering?
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Samuel M. Smith Ph.D.
242 East 600 North, Lindon Utah 84042-1662 USA
801-768-2768 voice
801-768-2769 fax
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"The greatest source of failure and unhappiness in the world is
giving up what we want most for what we want at the moment"
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Andreas Neumann
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8624 Grüt (Gossau ZH)
Switzerland
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