Andreas,<br><br><div class="gmail_quote">On Mon, Mar 23, 2009 at 5:45 AM, Andreas Hocevar <span dir="ltr"><<a href="mailto:ahocevar@opengeo.org">ahocevar@opengeo.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi,<br>
<br>
2009/3/22 Andrew Smith <<a href="mailto:laconical@gmail.com">laconical@gmail.com</a>>:<br>
<div class="im">> Andreas, you mentioned that if my data was in PostGIS I could use either a<br>
> WMS or WFS to get the data. If I went down the WMS path, I would have one<br>
> WMS for my base map layer, and another one for my text objects layer. My<br>
<br>
</div>You could also combine these into one set of image tiles. WMS has a<br>
layers parameter. So if your wms layer params has something like<br>
<br>
params.layers=["mybaselayer","myoverlay"];<br>
<br>
in it, both will be rendered in one image, with the overlay not<br>
occluding the base layer.</blockquote><div><br>This would be a good idea if the text data I wanted to show was static, but unfortunately it'll be changing every 5 seconds or so. If I integrated the base map and the text into one set of image tiles, the browser would need to reload all image tiles regularly to get the updated data. If the text objects are on their own layer, then the server will be doing less work to regenerate just the text images (parsing less data from PostGIS), and hopefully the refresh will be reasonably smooth because the base layer isn't changing. That's what I'm hoping anyway. I assume there are no performance implications I need to worry about if I'm redrawing a layer every 5 seconds? My guess is that OpenLayers is not typically used to show data that changes so quickly.<br>
<br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br>
<div class="im"><br>
> understanding is that the text WMS would return a tile map of images which<br>
> would be largely empty space with the occasional text value here and there.<br>
> I guess this layer would be transparent so as not to occlude the underlying<br>
> map images.<br>
<br>
</div>That's correct, you would have to add the transparent=true param for<br>
the overlay.<br>
<div class="im"><br>
> Meanwhile, the WFS would return the details about the text<br>
> labels and rely on OpenLayers to actually render the vector representations.<br>
<br>
</div>You can also get the details of text labels using a WMS GetFeatureInfo request.</blockquote><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
<div class="im"><br>
> You mentioned that WMS would be preferred if there were a 'huge number of<br>
> features' - I'm surprised that creating all those image tiles on the server<br>
> side is faster than adding x vector objects on the browser side (I will<br>
> probably have a few dozen at most). Is there a certain point where it just<br>
> makes more sense to do it on the server based on the number of objects you<br>
> want to displa<br>
<br>
</div>If you expect the number of your point to grow beyond ~100, you'll<br>
definitely be better off using WMS (especially if your users are on<br>
Internet Explorer).<br>
</blockquote><div><br>I assume this is because SVG is not used when rendering vector objects in IE, so there's a lot more overhead in showing vectors in that browser?<br><br>Cheers,<br><br></div></div>Andrew<br>