[OpenLayers-Users] Help needed with vectors

[Andreas Hocevar]

Hi,

On Mon, Jun 16, 2008 at 11:52 AM, realjax <jax at schildmos.nl> wrote:
> I need to draw a *large* number of vectors on a map. We are talking 300 to
> 2000 vectors.
> Drawing the features as true vectors is not an option because of (obvious)
> performance reasons, but I have found that when creating the vector as an
> icon the performance is relatively acceptable. Now I know that having so
> many features on one map is not recommendable -I'll fight my managers about
> it at some later time :-) - but truth is, it is not likely to go below 300
> ever so I just have to squeeze the most out of the browsers.

An option would be to use Layer.WMS for your vectors. I doubt that the
average human will be able to perceive a map with that many features.
If you use WFS, only the features for the current map extent will be
loaded.

> - Internet Explorer 6 is approx. fourteen times (!) slower then firefox. It
> takes over 7000 milliseconds to do the same here. Since I can't find a
> decent profiler for IE I have no idea where this lag is coming from. Can
> anybody shed some light on this? Is there a bottleneck in the VML rendering
> maybe ?

First of all, VML renders slower than SVG. And because rotation in VML
is much more expensive than in SVG. If you try to use unrotated
features, you will see that it is faster, but still slower than SVG.
But I suspect most of the time is eaten up by the rotation. A
workaround would be to provide separate icons for e.g. 12 or 16
angles. More different angles usually don't make sense in terms of
human perception.

Regards,
Andreas.