Problems Creating Projection File

[ScottAtherton1]

I was given some CAD Data and told it was in a 10TM projection, included in the meta data was the following information:

GEOGRAPHIC LOCATION:         Latitude: 49:0:0
                                         Longitude: 110:0:0
PROJECTION:            10 DEGREE TRANSVERSE MERCATOR
PROJECTION ID:         0202
CENTRAL MERIDIAN:      115
COMBINED SCALE FACTOR: 0
IGDS GLOBAL ORIGIN:    X = 500000    Y = -5000000
DESIGN SCALE:          1000000
DATUM:                 NAD83
COMMENTS:              1:1,000,000 POSITION FILE

This is my attempt at the projection file:

PROJCS["10TM",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",-5000000.0],PARAMETER["Central_Meridian",115.0],PARAMETER["Scale_Factor",0.0],PARAMETER["Latitude_Of_Origin",49.0],UNIT["Meter",1.0]]

If someone could explain where I am going wrong that would be fantastic, keep in mind I am a relatively novice user,
Thanks in advance

[MelitaKennedy]

Hi,

I see a few possibilities. Canadian data, right? The information doesn't match any of our existing 10TM definitions, unfortunately. First, change the central meridian to -115. (115W).

Also I would try changing the latitude of origin to zero. I think geographic location just identifies the area of the data, and may not have anything to do with the projection parameters. With the latitude of origin set to the equator, Y values will be around 5-6 million. However, with a -5000000 m false northing, that will reduce the size of the Y values.

Lastly, change the scale factor to 1.0. Scale factor is applied as a multiplier to the numbers coming out of the algorithm, before the false easting and false northing values are added.

Melita

[ScottAtherton1]

Yes it is data from Canada in fact this is what altalis has provided (the official data distributer of the Alberta Government). It looks like I am still missing something here, this is what the projection file looks like now:

PROJCS["10TM",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",5000000.0],PARAMETER["Central_Meridian",-115.0],PARAMETER["Scale_Factor",1.0],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]

Thank you for your help on this

[MelitaKennedy]

Hi,

Try changing the false northing to -5000000.

Melita

[ScottAtherton1]

Humm ok I tried that, and now when I bring the layer into Arcmap I am getting the Inconsistent extent Error message  

PROJCS["10TM",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",-5000000.0],PARAMETER["Central_Meridian",-115.0],PARAMETER["Scale_Factor",1.0],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]

[MelitaKennedy]

Can you post the data's current extents (using this coordinate system), plus a general idea of where it should be located?

Thanks,
Melita

[ScottAtherton1]

I can do even better than that, the data is from the following link
http://www.altalis.com/prod_base_small.html
it is the 1:1 million data and it covers all of alberta

[MelitaKennedy]

Okay, I downloaded the DWG. Ignore everything I said and what the metadata says. Just assign the NAD 1983 10TM AEP Resource prj to the data. A quick way to check it is to add the AltaLIS data to ArcMap. You should get a 'missing coordinate system' message; ignore it. Add some reference data. Set the data frame's coordinate system to the AEP Resource coordinate system. The reference data, as long as it has a coordinate system, will get projected on-the-fly and should line up.

Melita

[ScottAtherton1]

Alright now we are in business thank you very much, I don�??t fully understand why my approach didn�??t work it seems like it should have, was the meta data wrong?

[MelitaKennedy]

I don't know. I believe the metadata's correct for the CAD software, so someone working with it in that software would need to know that information. Because the data was georeferenced to a 'known' coordinate system, it just works in the GIS software.

Melita