topic Re: Defining Projection in Data Management Questions

Defining Projection

morganhunt — Fri, 08 Jul 2011 15:48:42 GMT

Hi, I am a newbie so please bear with me. I have downloaded some grids from the USGS and while I can open and view them in ArcView (9.2) there is no projection file. However, there was provided projection information on the website where I downloaded the grid. My issue is that when I go to define the projection for the grid, I can't locate the projection that they specified. I have copied below exaclty what I was given as to the projection of the grid:

For the merged aeromagnetic anomaly grid and map.

Projection = Spherical transverse mercator

Central meridian = 100Â° W.

Base latitude = 0Â° N.

Scale factor = 0.926

Spherical earth radius = 6,371,204 m

Horizontal datum = DNAG

Re: Defining Projection

MelitaKennedy — Mon, 11 Jul 2011 16:31:36 GMT

Hi,

If the files are still in Esri GRID format, make a text file called prj.adf and place this text in it:

projection transverse
units meters
parameters 6371204 6371204
0.926
-100 00 00
00 00 00
0.0
0.0

We don't have a separate spherical transverse mercator. Instead, you set the gcs/datum to use a sphere and that triggers the correct map projection equations.

If the raster's been converted to another format, try creating a text file called DNAG.prj and put this in it (as a single line)

PROJCS["DNAG",GEOGCS["GCS_STM1987",DATUM["D_STM1987",SPHEROID["STM1987",6371204.0,0.0]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-100.0],PARAMETER["Scale_Factor",0.926],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]

Put DNAG.prj into the ArcGIS install location's Coordinate Systems, Projected Coordinate Systems folder. Now you can browse to it and set it as a raster's coordinate system in Define Projection Tool or the data's property page in ArcCatalog.

Melita

Re: Defining Projection

morganhunt — Wed, 13 Jul 2011 18:38:20 GMT

Thank you, Thank you, Thank you!