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Transformations installed by default in ArcGIS

ArcGIS uses the EPSG codes for datum transformations.

NAD_1983_to_WGS_1984_1 - Any area

Transform _1 is a null transform.

All parameters are held at 0 and data does not move at all. Your data is defined as NAD83 in ArcGIS without shifting positions as collected by GPS. This ‘transformation’ reflects the fact that WGS84(1986) and NAD83(1986) are equivalent. The latest realizations of each datum have since migrated meters away from each other.

NAD_1983_to_WGS_1984_5 - Continental US and Alaska

Transform_5 is an updated version of NAD_1983_to_WGS_1984_1.

It was designed to move data between ITRF96/WGS84(G973) and NAD83(CORS96). This transformation needs to be updated. The centimeter level error resulting from failing to update from ITRF96 and ITRF00 is referred to here as “NAD83_5”.

NAD_1983_to_WGS_1984_3 - Pacific Islands

Transform_3 moves data between WGS-84 and NAD83 in the Pacific.

This transformation needs to be updated to incorporate corrected parameters in the last days of 2008. The error resulting from failing to update is referred to here as “NAD83_3”.

Recommended for manual installation in ArcGIS and ArcPad

The accumulation of ‘small errors’ in your data adds up quickly.

H-Star users in particular risk losing the centimeter-level accuracy afforded by the hardware to datum shifts introduced by failing to update software transformations. All users should ‘do the right thing’ and manually install the following transformations in ArcGIS. Instructions are included on this site.

Continental US and Alaska

Replace all instances of Transform_5 with NAD83(CONUS)CORS96 .

While transform_5 moves move data between ITRF96/WGS84(G973) and NAD83 (WHICH?), the newer NAD83 (CONUS) CORS96 transformation moves data between the latest realizations of WGS84/ITRF00 and NAD83 - or more specifically WGS84(G1150) and NAD83(CORS96). Your resulting data is true NAD83(CORS96) rather than “NAD83_5” resulting from the outdated ArcGIS transform _5.

Pacific Islands

Replace all instances of Transform_3 with ITRF_to_NAD83(PacP00). ITRF_to_NAD83(PacP00) moves data between WGS84 and NAD83(CORS96) for users in the Hawaiian and Marshall Islands and American Samoa. Users on Guam and others on the Mariana plate, use ITRF_to_NAD83(MarP00). Your resulting data is true NAD83(CORS96) rather than “NAD83_3” resulting from the outdated ArcGIS transform _3.  Be sure to see important PacP00 updates as of Jan 2011!