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I have data in NAD 1983 Zone 20 and want to transform it to NAD 1983 CSRS Zone 20. I found this source: https://community.esri.com/thread/6772 which states:

  • NAD_1983_To_NAD_1983_CSRS_4 > 1950 Canada - Newfoundland, New Brunswick, & Nova Scotia offshore

Since I am not native in English, the word "offshore" bothers me. I hope somebody could confirm if this is the best transformation for data located in the Nova Scotia mainland or suggest a better transformation?

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    Offshore would mean one of the only parts of Nova Scotia that is in the Atlantic (Cape Breton or Sable Island). The issue here is that New-Brunswick is actually further west than Nova Scotia, bordering Quebec. I'm somewhat perplexed by the idea that NS wouldn't work as it's between NB and NL (Newfoundland). My main question is, though, do you really have to work in CSRS? I did work for provincial agencies recently and we used vanilla NAD83. – Gabriel C. Nov 29 '18 at 14:23
  • That's a valid question. :) But unfortunately, some of my data are in NAD 1983 CSRS Zone 20 and some in vanilla NAD83. – Thomas Zuberbühler Nov 29 '18 at 16:22
  • I would contact ESRI. Or simply forego the problem and reproject using GDAL/QGIS which won't raise any issue with transformations. The variations should be extremely minimal anyway and unless you need topology to exactly line up between data sets (if that's an issue), it should be fine. – Gabriel C. Nov 29 '18 at 16:52
  • I believe you would need to download the files for the transformation on the local or national government website, because ERSI does not provide those files with the installation. – FSimardGIS Nov 29 '18 at 17:41
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    @FSimardGIS I had looked into that and when reading documentation from Geonova, it seems they don't have a .gsb for original to CSRS transformation. – Gabriel C. Nov 29 '18 at 21:28
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If you check the official definition in the EPSG Geodetic Data Registry, it lists:

Remarks: Used as part of NAD27 to/from WGS 84 transformation for offshore oil operations - see code 8647. Scope: Accuracy 1 to 2 metres. Used for oil industry operations only. Information Source: Various oil industry sources.

The transformation parameter values are zeroes, so it's treating NAD 83 and NAD 83 CSRS as equivalent within 1-2 m of accuracy.

Esri has been working on getting permission to redistribute the provincial NTv2 transformation files but we need to deal with each province separately.

Nova Scotia plans to release (not sure if it's available yet) a new NTv2 file but it converts between ATS77 and CSRS 2010.0. This would replace the older NTv2 file which converts between ATS77 and CSRS 1997.0. The paper is online here.

Even if you got either NTv2 version, there's no transformations available between ATS77 and the "original" NAD 83 that I know about.

Disclosure: I work for Esri and am on the subcommittee that maintains the EPSG registry.

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