Civil 3D 2012 Coordinate system scale factors are wrong for 6TM and 3TM?

[ericcollins6932]

I was recently setting up a new install of Civil 3D 2012 and was going to set the default coordinate system to 3TM (CM=114°W) when I realized the scale factor was set to 1.0 at the central meridian.

It should be 0.9999. I checked some others and they are all the same. I also checked the 6TM projection and it is also set to 1 although it should be 0.9992

Below is the WKT(ESRI) out of Civil for EPSG code 3401:

PROJCS["CANA83-10TM115",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.000,298.25722210]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",0.000],PARAMETER["False_Northing",0.000],PARAMETER["Scale_Factor",1.000000000000],PARAMETER["Central_Meridian",-115.00000000000000],PARAMETER["Latitude_Of_Origin",0.00000000000000],UNIT["Meter",1.00000000000000]]

Looking up the .PRJ for EPSG 3401, the published standard is:

PROJCS["NAD83 / Alberta 10-TM (Resource)",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-115],PARAMETER["scale_factor",0.9992],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1]]

Is anyone aware of this behaviour in Civil 2012? Has it been fixed in later versions? Thanks in advance.

[BrianHailey]

I'm not real familiar with how the coordinate systems are set up. If you give me instructions on how to check it, I can check it in 2014 for you.

Also, you might want to post this in the Map discussion group. They might be able to provide better answers as they deal with coordinate systems a lot more then Civil 3D folks do.

[ericcollins6932]

In 2012, one can keyin mapcslibrary.

Set your Category filter to Canada, Provinces and look for Code CANA83-3TM114

Click on View, -WKT

The WKT ESRI in my 2012 version looks like this:

PROJCS["CANA83-3TM114",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.000,298.25722210]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",0.000],PARAMETER["False_Northing",0.000],PARAMETER["Scale_Factor",1.000000000000],PARAMETER["Central_Meridian",-114.00000000000000],PARAMETER["Latitude_Of_Origin",0.00000000000000],UNIT["Meter",1.00000000000000]]

Scale factor is 1.0, and it ought to be 0.9999 for 3TM at the central meridian.

Thanks in advance!!

[sirjoelsph · Accepted solution]

In 2014 SP1 i get this:

PROJCS["CANA83-3TM114",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.000,298.25722210],TOWGS84[0.0000,0.0000,0.0000,0.000000,0.000000,0.000000,0.00000000]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",0.000],PARAMETER["False_Northing",0.000],PARAMETER["Scale_Factor",0.999900000000],PARAMETER["Central_Meridian",-114.00000000000000],PARAMETER["Latitude_Of_Origin",0.00000000000000],UNIT["Meter",1.00000000000000]]

Looks like the have the Scale Factor at 0.9999 like you wanted.

[ericcollins6932]

Yep, this will contribute 100 PPM of error as the work I do is pretty much in the vicinity of the central meridian. That's a huge error. Am curious when Autodesk corrected this. Will have to dig into release notes unless anyone knows.

[BrianHailey]

In 2013, the scale factor is 0.9999 as well.