Overview
FME supports conversions between coordinate systems using different datums. Many datum transformations are not mathematically definable and require a grid of shifts. If you attempt to make a datum transformation of this kind without the appropriate grid shift file in place, FME will stop the translation. This article shows examples of how you can control which grid shift files are used and in what order.
To better understand how FME handles grid shift files, please refer to the online documentation.
In many cases, you need to contact the responsible authority (provincial ministry, etc.) to obtain the grid shift file. We are not always allowed to distribute them ourselves.
How Grid Shifts are Configured in FME
When converting datums, FME chooses the grid shift file to use from the list configured in Tools - FME Options - Coordinate Systems in the appropriate Grid Transformation.
HARN / HPGN Network in North America
When this was originally designed, there were only six HPGN files (HARN used to be called High Precision GPS Network, and that's why the files are named *HPGN.las). At the time, in all cases of overlap, the results were the same from any overlapping file, but this is no longer true. The design was intended to make HARN look like one datum and not preclude converting data that might extend beyond or over a grid file boundary. By making a selected wihpgn.las (Wisconsin) the first entry, for example, it becomes the default file.
If you only need high precision in one geographic region, for example, the state of Wisconsin, you could remove the other entries and gain a slight performance improvement as well as not have to worry about grid shift file order.
This same principle applies to NAD83, for example. The alaska.las files, the conus.las files, and the hawaii.las files are all listed in the Grid Transformation dialog. Users can order the files as needed. Thus, NAD83 is a single datum, and the system avoids prompting for which file to use.
Grid Shift Files by State
Here is a listing of States and their associated grid shift files.
For more background on NADCON and a complete list of US grid shift files, see State File Name
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Alabama ALHPGN
Arkansas ARHPGN
Arizona AZHPGN
California CNHPGN (Above 37 degrees latitude)
California CSHPGN (Below 37 degrees latitude)
Colorado COHPGN
Florida FLHPGN
Georgia GAHPGN
Hawaii HIHPGN
Idaho-Montana EMHPGN (East of 113 degrees longitude)
Idaho-Montana WMHPGN (West of 113 degrees longitude)
Iowa IAHPGN
Illinois ILHPGN
Indiana INHPGN
Kansas KSHPGN
Kentucky KYHPGN
Louisiana LAHPGN
Maryland - Delaware MDHPGN
Maine MEHPGN
Michigan MIHPGN
Minnesota MNHPGN
Mississippi MSHPGN
Missouri MOHPGN
Nebraska NBHPGN
Nevada NVHPGN
New England NEHPGN (CT,MA,NH,RI,VT)
New Jersey NJHPGN
New Mexico NMHPGN
New York NYHPGN
North Carolina NCHPGN
North Dakota NDHPGN
Ohio OHHPGN
Oklahoma OKHPGN
Pennsylvania PAHPGN
Puerto Rico-Virgin Is PVHPGN
South Carolina SCHPGN
South Dakota SDHPGN
Tennessee TNHPGN
Texas ETHPGN (East of 100 degrees longitude)
Texas WTHPGN (West of 100 degrees longitude)
Utah UTHPGN
Virginia VAHPGN
Washington-Oregon WOHPGN
West Virginia WVHPGN
Wisconsin WIHPGN
Wyoming WYHPGN