[OpenLayers-Dev] Grid-style loading of Markers

Matt Williamson MatthewDW at gmail.com
Wed Feb 10 18:04:41 EST 2010


Ah, thanks for this--you hit on part of my misunderstanding, that not all strategies in trunk are clustering strategies. I didn't realize that the BBOX strategy actually loaded more data from the server.

So I experimented with the BBOX strategy, and unfortunately it doesn't really fit my needs, for two reasons.

One (the lesser), I have a problem with data density--if I just select the top (most "interesting") 150 points in the BBOX, they may all be in one place. Consider Salt Lake City, Utah, which is a large city in the middle of mountain wilderness. If I center the map showing Utah, I get 150 points in Salt Lake City, and none in the mountains--I'd like to be able to display points in data-sparse areas, even if they're lower priority points, when there is room. My tile generation routine uses a computationally expensive mechanism to fill those gaps--but if I can pre-generate them, then there's no real-time cost.

Two (the greater), the BBOX strategy does not load more points when zooming in. If the map starts centered on Utah, then the user zooms out to the whole U.S., then zooms back in on Texas, it doesn't load new points, because the zoomed-in BBOX is still within the old zoomed-out BBOX. Since the new viewport is still within the last gathered dataset, it does not attempt to get more features. If there's a way to configure the BBOX strategy so this is not the case, please let me know!

So, am I to assume from your comments that the BBOX strategy is still a valid option? Do you happen to know if it still even works with 2.8 or will with 2.9? And/or, that functionality hasn't been merged into some other object in the mainline trunk or otherwise made obsolete by some other new functionality? I just don't want to invest in obsolete or orphaned code, especially if there's something better.


Second question, what interested me so much 

On Feb 10, 2010, at 12:26 AM, Eric Lemoine wrote:

> On Tuesday, February 9, 2010, Matt Williamson <MatthewDW at gmail.com> wrote:
>> Devs,
>> I posted this to the Users list, but the devs list might have made more sense, since part of the question has to do with the vector behaviors sandbox in SVN...
>> I am looking for a way to load statically stored "tiles" full of marker information, so I can do progressive disclosure of a large point dataset (and I don't have access to Geoserver or similar server-side component). My maps are spherical mercator/Google based, so loading the markers in tiles makes sense.
>> I found this post on the dev list, which sounds pretty much exactly like what I want to do...
>> http://openlayers.org/pipermail/dev/2009-January/004222.html
>> But it was using stuff from the vector behaviors sandbox, which hasn't been touched in a year, it looks like.
>> So my question is: Is there a standard way to do something like this? From static tile files on the server filesystem (probably GeoJSON format)? I know the "right" answer is to set up a WFS server somewhere, but that's out of the question in the short term. Plus, my point locations change very seldom, so Geoserver would really be overkill anyway.
>> I was going to try writing my own OpenLayers.Layer.Grid and OpenLayers.Tile subclasses, but I wanted to check if there's an existing way to do this that I've missed, or if the OpenLayers.Strategy.Grid stuff in the vector behaviors sandbox stuff is still a valid way to go.
> Hi. Just like the BBOX strategy the grid strategy sends requests with
> a BBOX filter so a web service that can "decode" that filter is
> assumed.
> Cheers,
> -- 
> Eric Lemoine
> Camptocamp France SAS
> Savoie Technolac, BP 352
> 73377 Le Bourget du Lac, Cedex
> Tel : 00 33 4 79 44 44 96
> Mail : eric.lemoine at camptocamp.com
> http://www.camptocamp.com

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