Difference between NAD_1983_CSRS_MTM_9 and NAD83(CSRS) / MTM zone 9 ?

[mastc26]

Hi,

I would like to know if there is a difference between NAD_1983_CSRS_MTM_9 and NAD83(CSRS) / MTM zone 9 coordinate systems in ArcMap 10.6.

Here are the characteristics for NAD_1983_CSRS_MTM_9:

Projected Coordinate System: NAD_1983_CSRS_MTM_9
Projection: Transverse_Mercator
False_Easting: 304800.00000000
False_Northing: 0.00000000
Central_Meridian: -76.50000000
Scale_Factor: 0.99990000
Latitude_Of_Origin: 0.00000000
Linear Unit: Meter

Geographic Coordinate System: GCS_North_American_1983_CSRS
Datum: D_North_American_1983_CSRS
Prime Meridian: Greenwich
Angular Unit: Degree

Here are the characteristics for NAD83(CSRS) / MTM zone 9 :

Projected Coordinate System: NAD83(CSRS) / MTM zone 9
Projection: Transverse_Mercator
false_easting: 304800.00000000
false_northing: 0.00000000
central_meridian: -76.50000000
scale_factor: 0.99990000
latitude_of_origin: 0.00000000
Linear Unit: Meter

Geographic Coordinate System: NAD83(CSRS)
Datum: NAD83_Canadian_Spatial_Reference_System
Prime Meridian: Greenwich
Angular Unit: degree

The layer of my project in ArcMap is in NAD_1983_CSRS_MTM_9, but I noticed the shapefiles I exported from Pix4Dmapper are in NAD83(CSRS) / MTM zone 9 when I import them in ArcMap. It seems to me like it is the same coordinate system, therefore I don't understand why there are two ways to "write" it in ArcMap. Is there a real difference (I notice the Datum is not written the same either)?

Thank you for the info!

[Pål_Herman_Sund · Accepted solution]

Seems to be the same reference system (in practice) - but the PRJ file describing the pix4dmapper shapefile is not made according to the way ESRI does it (ESRI WKT) . There are several ways for describing a reference system (you will be surprised) as Autodesk, MapInfo, PROJ etc all have their own "WKT".

If you do not like the difference use the "Define Projection" tool to set the description for the shapefile. 

[MelitaKennedy · Accepted solution]

We modeled the Esri projection engine's coordinate system and transformation structures after EPSG's but didn't always agree with some of their decisions. Later, once ISO19111 codified the coordinate reference system data model (and in the last few years, coordinate operations/transformations), it was somewhat different. EPSG has updated their data model to more closely match ISO19111. Esri has generally remained unchanged. We have the EPSG names as synonyms so if we can identify the object, you should see the WKID if you look at its details. If it's listed as unknown, then for whatever reason, we could match the definition against our version. If you leave the coordinate system as-is, the only thing it will affect is if you need to transformation between NAD 1983 CSRS and another GCS. Because we don't 'recognize' the GCS, we won't be able to find any transformations for it.

Melita