Web Mercator to CSRS Datum Transformation

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10-29-2021 01:13 PM
Status: Open
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MatthewCriel
New Contributor III

When using a ESRI Web mercator Basemap ArcGIS Pro cannot find the native transformation for Canadian CSRS data. 

The only workaround is a custom transformation.

I think ESRI should implement built in transformations between Web Mercator and NAD 1983 UTM CSRS

This would cut down on the errors experienced by GIS technicians.

7 Comments
N_W_S_E

I second this!

KoryKramer

Thank you for the comment @N_W_S_E   I took a look and it doesn't appear that you added your kudos to the idea. While comments are important, kudos (the number of votes) that an idea receives is one of the primary pieces of data that we use to determine traction and trends as we monitor idea activity over time.

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Kory

BojanŠavrič

@MatthewCriel Thank you for submitting your idea. 

I believe ArcGIS Pro already supports several transformations between NAD 1983 (CSRS) and WGS 1984 geographic coordinate systems. If I set the map to NAD 1983 CSRS UTM Zone 16N (WKID::3160), I get the following possible transformation paths:

Bojanavri_1-1649265744111.png

In which coordinate system is your Canadian CSRS data? If it is using one of the NAD 1983 (CSRS) realizations (e.g. NAD83 (CSRS) v6, WKID::9644), we do not have any defined because none of the are registered with EPSG nor we can find them on Natural Resources Canada's website.

 

GrantHopkins1

@BojanŠavrič , how can we (the customers) help Esri get this information? It's very frustrating and difficult for us to know with certainty which transformations we should be using.

Could Esri proactively reach out to the Province (https://www.ontario.ca/page/geodesy) or NRCAN (https://www.nrcan.gc.ca/maps-tools-and-publications/tools/geodetic-reference-systems/canadian-spati...) to get what is needed to make this happen? I'd do it if I knew enough about the subject to ask.

I'm willing to help out if I can.

Thanks,

Grant

MattCriel

Hello @GrantHopkins1 @BojanŠavrič 

I have used this  2 part transformation with some success, I think Arcpro uses it by default now:

MattCriel_0-1655756905753.png

I doubt it is as accurate as the custom Ontario CSRS transformation from the province, but it seems to project the data properly.

@GrantHopkins1 Have you tried this transformation? 

 

GrantHopkins1

@MattCriel, thanks for your quick response! No, I have not tried that one but I'll have a look.

I've been using this as my guide: Datum Transformations in ArcGIS Online | Web Maps |Data Visualization (esri.ca) but I'm still not convinced things are set up or lining up properly when I'm not seeing an option for CSRS v6. Perhaps the difference is so small that I wouldn't notice for my uses but I just haven't seen anyone with expertise lay it out that way.

Thanks again!

Grant

BojanŠavrič

Hello @GrantHopkins1,

I can imagine how difficult it is to know all little details about transformations and coordinate systems. Every country does this things a bit differently, which does not help GIS users. All that knowledge comes with experience and, with time, it gets easier.

In cases when there is no transformation to desired GCS listed in the Geographic and Vertical Transformation Tables, I would suggest you reach out to your local Esri's distributor. I expect they would know any specifics for the country and have contacts to the local agencies. They can work with the agencies to obtain necessary information about possible transformations and clear any license restrictions. Once they obtain the information, they can contact us with details and we implement transformations.

For the Ontario province, we do have definitions for transformations to NAD83 (CSRS) v3, WKID::8240, provided by NRCAN (I know this is not what your are looking for but it might help.):

Bojanavri_0-1655920314659.png

Due to license restrictions at the time we added these definitions into ArcGIS, we do not distribute the necessary NTv2 files with the ArcGIS Coordinate Systems Data software component. If you wish to try them out, you can download them from the NRCAN website or from here and add them to a specific CoordinateSystemsData\pedata subfolder on your machine. Files are sorted into folders by transformation method name, such as NTv2 or vertical\geoid. For these four transformations, you should add the NTv2 files to <System Drive>\Program Files (x86)\ArcGIS\CoordinateSystemsData\pedata\ntv2 folder. Please contact your local distributor if you have any troubles or need more detailed instructions. 

To comment on @MattCriel's suggestion above. ArcGIS Pro is limited to 2-step transformation paths when projecting data on-the-fly. Unfortunately, this results in transformation paths that might not be geodetically correct (aka transforming between Canadian GCS-es via world-wide WGS 1984 GCS). This happens often when country has several GCS-es in use and one needs to transform/project data in several steps via multiple GCS realizations. For some applications, transforming data via WGS 1984 works OK, but I would not recommend it in general.

I hope this helps,
Bojan