[Qgis-user] WMS Image Projection

[Springfield Harrison]

Hello Andreas & Kirk,

Thanks very much for your suggestions.  I also got help from the 
regional Gov't GIS Manager.  He suggested trying the REST source 
(server?) through the QGIS ArcGIS Map Service 
(https://mapservices.crd.bc.ca/arcgis/rest/services).  It worked and the 
misalignment disappeared!  In QGIS, toggling the two different 2019 
orthophotos showed them jumping by about 1.5 m. Several miles away, the 
result was the same.

The REST source did the trick although the underlying data is the same.

The REST property lines were identical to the WMS version.

Not sure why this works but will use the REST server in the future.

Thanks again for your help . . .

-----
Cheers, Spring



On 08/Apr/2021 05:48, kirk wrote:
> Hi Springer.
> My mistake, you will require a local grid shift file, BC_93_05.gsb. 
> The NTv2 is a national NAD27
> to NAD83 grid shift file. The BC_93_95 provides localized conversion 
> from Nad83 (original) to Nad83 (csrs).
>
>
> Sent from my Galaxy
>
>
> -------- Original message --------
> From: Springfield Harrison <stellargps at gmail.com>
> Date: 2021-04-08 5:24 a.m. (GMT-04:00)
> To: Andreas Neumann <a.neumann at carto.net>
> Cc: qgis-user <qgis-user at lists.osgeo.org>
> Subject: Re: [Qgis-user] WMS Image Projection
>
> Hi Andreas,
>
> Thanks for the reply, I'll try to clarify:
>
>  1. Version is 3.16.4
>  2. The two municipal sources are being viewed in their own web
>     windows and are displaying the same data
>      1. They are the source of the property lines for my GIS
>         (downloaded shapefile) and the orthophoto (WMS link, not
>         resident TIFF or other)
>  3. The property lines are EPSG:3157 - NAD83(CSRS) / UTM zone 10N -
>     Projected, and from the municipal source.  I've attached the
>     shapefile if you have the time.
>  4. In QGIS, the ortho is loaded from the WMS source
>      1. https://mapservices.crd.bc.ca/arcgis/services/OrthoImagery2019/MapServer/WMSserver
>      2. EPSG:26910 - NAD83 / UTM zone 10N - Projected
>  5. The project CRS is EPSG: 26910 but it doesn't seem to change
>     anything by changing that or the source projections (at least
>     within versions of NAD83 UTM Zone 10N)
>  6. Thus, the same information displays differently online /versus/ in
>     QGIS.
>      1. The shift seems to be 1.5 m +/-, quite a lot for what I'm
>         trying to do (building permit with tight setbacks).
>      2. These are commonly used projections for our neck of the woods
>      3. The two images I sent earlier depict the differences; in QGIS,
>         earlier orthophotos show a similar or worse displacement. Not
>         so on the municipal web viewer.
>  7. I've read up on projections in the tutorial and Help file, no
>     revelations there, at least that I could see.
>
> Thanks very much for any thoughts you may have.
>
> -----
> Cheers, Spring
>
>
> On 08/Apr/2021 00:47, Andreas Neumann wrote:
>>
>> Hi,
>>
>> Are there two different CRS involved here? Are the vectors (parcel 
>> boundaries) in a different CRS than the orthoimages? This might be a 
>> problem of a missing grid-shift file in QGIS.
>>
>> It is also unclear for me if you load your Orthoimages locally (from 
>> tiff-files as well) or from WMS (or both) and only one of them is 
>> shifted?
>>
>> Can you also add information what QGIS version with what proj version 
>> you use? You can find this information in the about dialogue in the 
>> help menu.
>>
>> Greetings,
>>
>> Andreas
>>
>> On 2021-04-08 02:37, Springfield Harrison wrote:
>>
>>> Hello All,
>>>
>>> Re obtaining orthophotos from a WMS server.
>>>
>>> Locally we have orthophotos that can be brought into QGIS using the 
>>> WMS service.  They are also viewable on the local government web map 
>>> service.  In both cases I can compare them to the property lines 
>>> which are from the same source.
>>>
>>> On the government web pages (2), the orthophotos and the lot lines 
>>> appear to coincide very well.  In QGIS, the same two layers are 
>>> quite misaligned.
>>>
>>> One would suspect a CRS problem but changing the CRS of the Project 
>>> and the WMS image in QGIS has no effect.  Even followed the tutorial 
>>> to no effect.
>>>
>>> I'm attaching screen shots of the two results.  Ant thoughts would 
>>> be appreciated, thank you . . . .
>>>
>>> -----
>>> Cheers, Springfield Harrison
>>>
>>>
>>>
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>>
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