[mapguide-internals] Re: OpenLayers + SVG = MapGuide Vector Viewer

[Traian Stanev]

In short:

It renders everything with canvas. There is a spatial index, which the Javascript uses to render what's visible and skip whatever is not. However, it is not an R-Tree -- it is similar to the spatial index I used in the FDO SQLite provider, with the added support for partially populated index as data is asynchronously streamed in from the web server on demand. There are some significant performance advantages to this spatial index compared to an R-Tree.

Geometry+properties are streamed to the client in JSON format. The spatial index is also streamed in compressed JSON chunks to the client, depending on what areas the user zooms in to.

The really neat part is that there is no server process at all (so nothing to crash on the server side apart from Apache). The data (features and spatial index) is pre-computed from FDO format into JSON chunks, using some magic sorting which ensures that the JSON chunks are all fairly small and spatially coherent. Again, this sort is the same as is done in the FDO SQLite provider. Since the browser simply requests JSON files, it enables easy caching of the chunks both on the client and on the server tier.

The UI is done with yUI, which is pretty simple to use and quite effective.

Of course if you are really determined, you can see all the code in the Javascript that your browser cached. :)

Traian




-----Original Message-----
From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Crispin_at_1Spatial
Sent: Thursday, September 16, 2010 3:58 AM
To: mapguide-internals at lists.osgeo.org
Subject: [mapguide-internals] Re: OpenLayers + SVG = MapGuide Vector Viewer


Stunningly simple and effective example - could you elicit us with a little
of the architecture behind the interface please?
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