Canadian Spatial Reference System (CSRS) High Precision Datum

From Fmepedia

Created by: Dean Hintz

CSRS stands for Canadian Spatial Reference System. This is the current geodetic baseline used for performing surveys within Canada. Within FME, CSRS refers to the datum used for the highest precision coordinate systems typically used for survey data. In North America, most people are familiar with the NAD27 and NAD83 datums, and that conversion between them can result in shifts of up to 100m or so. CSRS uses a version of NAD83 updated in 1998 and typically involves shifts in the sub metre range. Thus, most users dealing with national or provincial scale maps are happy with the usual NAD83 and it is only survey level users that are concerned with CSRS. These include CSRS versions of the UTM grids and the Canadian Conformal Conic among others. For more on CSRS see: http://www.geod.nrcan.gc.ca/geodesy/reference/index_e.php (7 pages)

Due to the high precision required, CSRS always requires grid shift files. NTV2 is the grid shift for NAD27 to NAD83 conversion for all of Canada and is available from the FME gridshift installer. However, CSRS requires a different grid shift file for every province, and as Safe is not permitted to distribute these, they must be obtained from the relevant provincial ministry responsible for geodesy. For web links on where to obtain these, see: http://www.geod.nrcan.gc.ca/prov_contact/index_e.php

Before changing your FME gridshift coonfiguration, its a good idea to understand how FME handles grid shift files. Go to FME Workbench Help menu and choose Coordinate Systems help - Datums - Grid shift files. It used to be that you needed to manually edit some grid shift files or use Universal Translator to edit others but everything can now be managed from within Workbench.

You can also see the info at: http://www.safe.com/support/gridshift/index.php which includes a link to NRCan which in turn has links to the provincial websites of the ministries responsible for distributing the grid shift gsb files.

Its also good to take a step back and see if high precision provincial data is what you really want. First confirm what your desired destination coordinate system is. Consider 'Lambert Conic projection for Canada'. There are about 10 different variants of this projection available within FME.

If you choose :

 CS_NAME: CANLAMB-CSRS
 DESC_NM: Lambert Conformal, Canada, CSRS
 DT_NAME: CSRS

Since this is high precision, it requires a provincial gridshift file, and since the default in FME is PQA8398.gsb (Quebec) you get an error saying this isn't available.

Unless you really need mm level accuracy, and you already have all your data in high precision CSRS, you may be better off choosing a NAD83 based variant of the Lambert Conformal, Canada, such as:

 CS_NAME: CANLAMB-83
 DESC_NM: Lambert Conformal, Canada, NAD83
 DT_NAME: NAD83

or the WGS84 variant:

 CS_NAME: Canada-LCC
 DESC_NM: Lambert Conformal Conic projection for Canada, Meter
 DT_NAME: WGS84

Of course, this all depends on what datum you are using in general for your project.

So if you are getting an error such as

 The following Canadian grid shift file was specified, but not found:
 \FME\Reproject\GridData\Canada\PQA8398.gsb. 
 This reprojection will be inaccurate for Canadian data.

To sum up, if you really just want your data in NAD83 or WGS84, double check your coordinate system destination setting and make sure you chose the right one. If you are still certain that you want the high precision coordinate system, then contact the relevant provincial ministry, obtain the grid shift .gsb file from them, then place it in the \FME\Reproject\GridData\Canada\ directory and then check your Workbench - Options - Datum Gridshift settings to make sure that that provicial gridshift file is properly referenced and at the top of the list.