[OpenLayers-Dev] RE: WMS request mod

[Dominik Mikiewicz]

Using some kind of reprojection in the middle would be ok but would consume
resources as Bob mentioned. Although if you are displaying your data in
large scales, staying with 4326 should be ok for visualization.
In one of my apps I display data that comes in 4326 over google maps and I
am happy with the accuracy even though the data is fairly detailed -
planning information with extents derived from catastral boundaries. So I'd
say if you are presenting your data at a county,  or city level or in larger
scales you should not notice any particular problems. If you are to display
your data at a country or continental level do consider a reprojection.

You mentioned your data appears in the right position over your basemap. I
think this should be your benchmark actually. If it looks ok, and you don't
need a razor sharp accuracy stay with what looks ok and works already.


-----Original Message-----
From: openlayers-dev-bounces at lists.osgeo.org
[mailto:openlayers-dev-bounces at lists.osgeo.org] On Behalf Of ray.diciaccio
Sent: Friday, May 20, 2011 5:05 PM
To: dev at openlayers.org
Subject: [OpenLayers-Dev] RE: WMS request mod

Ok, so it sounds to me like the "right" way to do this would be to follow
Bob's suggestion and use some middleware piece to do the reprojection --
that way I wouldn't need to worry about the distortion?

- Ray


Dominik Mikiewicz wrote:
> 
> Yeah, I should have added - large scales are fine (> 1m, 500k), small are
> distorted.
> 
> -----Original Message-----
> From: andreas.hocevar at gmail.com [mailto:andreas.hocevar at gmail.com] On
> Behalf
> Of Andreas Hocevar
> Sent: Friday, May 20, 2011 9:26 AM
> To: Dominik Mikiewicz
> Cc: Ray Di Ciaccio; openlayers-dev at lists.osgeo.org
> Subject: Re: [OpenLayers-Dev] WMS request mod
> 
> This approach will only work well for tiles that are near the equator,
> or don't span over a wide range of latitudes. It is basically the same
> thing that happens when you use the not recommended reproject: true
> option for Layer.WMS.
> 
> Andreas.
> 
> On Fri, May 20, 2011 at 8:54 AM, Dominik Mikiewicz
> <dominikmikiewicz at o2.pl> wrote:
>> This should work just fine. There won't be a serious performance hit
> either as you only recalculate bbox and change srs on the clientside. I do
> it quite often and even extended a wms layer class so I can quickly set up
> my 4326 layers to work with spherical Mercator.
>> However you may experience some issues with tile caching as sometimes the
> precision may vary from browser to browser. Another thing is the
> getFeatureInfo request - make sure you send correct cords if you are going
> to use it.
>> dom
>>
>> -----Original Message-----
>> From: openlayers-dev-bounces at lists.osgeo.org
> [mailto:openlayers-dev-bounces at lists.osgeo.org] On Behalf Of Ray Di
> Ciaccio
>> Sent: Thursday, May 19, 2011 6:00 PM
>> To: openlayers-dev at lists.osgeo.org
>> Subject: [OpenLayers-Dev] WMS request mod
>>
>> Sorry for the previous messed up message. Let me try this again:
>>
>> Hi all,
>>
>> I'm in what I'm guessing is a fairly common situation -- I'm using
>> Google Maps as my baselayer (so map is in EPSG:9009l3 projection) and
>> I'm trying to load an overlay from a WMS which I have no control over.
>> It only offers data in EPSG:4326. The WMS request generated by
>> OpenLayers will be for CRS=EPSG:900913 and the BBOX values will be in
>> EPSG:900913. This obviously won't work if the WMS only offers EPSG:4326.
>> My solution to this problem was to override
>> OpenLayers.Layer.WMS.getFullRequestString() so that it uses the
>> projection that I set for that particular layer -- it changes the
>> CRS/SRS param to whatever the layer projection is, and it transforms the
>> BBOX values from the map projection to the layer's projection. This way
>> I get a valid request for the WMS and it's loaded in the correct
>> location on the basemap. My question is whether this is the right
>> approach to this situation and whether there may be unforeseen
>> repercussions to these changes I made.
>>
>> Thanks!
>> - Ray
>>
>> --
>> Ray Di Ciaccio
>> MIT LL, Group 42
>> 781-981-2024
>> ray.diciaccio at ll.mit.edu
>>
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> 
> 
> 
> -- 
> Andreas Hocevar
> OpenGeo - http://opengeo.org/
> Expert service straight from the developers.
> 
> _______________________________________________
> Dev mailing list
> Dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/openlayers-dev
> 


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