[OpenLayers-Users] Some help with persistent layers and web server reponses.

[Eric Lemoine]

On Wednesday, August 11, 2010, Nathan Silver <nsilver at imagesensingca.com> wrote:
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> Hello all,
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> I’ve looked at  Peter Robbins’ example of a
> persistent layer using GeoJSON (http://maps.peterrobins.co.uk/files/ol6.html)
> which is well behaved. I’ve been trying to duplicate the entire structure.
> I have my own IIS 7.5 running on Windows 7 which in turn is connected to a SQL
> Server 2008 DB. Once I can get OpenLayers to send the right query to IIS, I’ll
> be away to the races. Here’s what’s confounding me.
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> The working example issues a GET to retieve the GeoJSON data.
> The vector layers is defined like this:
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> var vectorLayer = new OpenLayers.Layer.Vector("Line
> Vectors", {
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> styleMap: sm,
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> eventListeners: {
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>  "featuresadded":
> dataLoaded
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>  },
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> strategies: [
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> new
> OpenLayers.Strategy.Fixed(),
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> saveStrategy
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> ],
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> protocol: new OpenLayers.Protocol.HTTP({
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> url:
> "/cgi-bin/fs/workspace/",
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> format: new
> OpenLayers.Format.GeoJSON({
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> ignoreExtraDims:
> true,
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> internalProjection:
> map.baseLayer.projection,
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> externalProjection:
> wgs84
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> })
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> })
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> });
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> My code only issues an OPTIONS request to the web server,
> something the working example never does. If I step through the OpenLayers code
> with Firebug, not only do I not see the OPTIONS request, I don’t see anything
> hitting the webserver at all. My vector layer is defined like this:
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> var vectors = new OpenLayers.Layer.Vector("Vector
> Layer", {
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> style: {
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> strokeColor:
> "blue",
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>                 strokeWidth:
> 3,
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> cursor: "pointer"
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> },
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> eventListeners: {
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> "featuresadded":
> dataLoaded
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> },
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>                 strategies:
> [
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>                                 new
> OpenLayers.Strategy.Fixed(),
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>                                 saveStrategy
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> ],
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>                 protocol:
> new OpenLayers.Protocol.HTTP({
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>                                 url:
> "http://10.0.1.26/roads.aspx",
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>                                 format:
> new OpenLayers.Format.GeoJSON({
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>                                                 ignoreExtraDims:
> true,
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>                                                 internalProjection:
> map.baseLayer.projection,
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>                                                 externalProjection:
> wgs84
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> })
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>  })
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> });
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> If someone can help me understand why OpenLayers is
> requesting “OPTIONS” from the server (which I can’t even see
> from grepping  or stepping through the code), and what I might need to go
> in order to get these two piece glued together, I would really appreciate it.


Hi.

I'm pretty sure you are facing the Same Origin Policy issue. The
OPTIONS request you're seeing is the "preflighted" request the browser
sends in your back. See
<https://developer.mozilla.org/en/HTTP_access_control>. To solve the
problem the GeoJSON service and the service providing the web page
must be available at the same domain.

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