Differential Correction: Big Changes with new NAD83(2011) Print

"OLD" listings removed from CBS in Oct 2012

Previously Pathfinder Office’s Community Base Station(CBS) list reported base station coordinates in both “NEW” and "OLD"versions to reflect allow users to choose a preferred reference frames to view coordinates. helped users gradually transition to the National Adjustment 2011 (NA2011).

CORS Station GARL is shown below but the same choice apply for any CORS stations  –

1) “NEW’ or “Derived from IGS08”

CORS, GARLIC (GARL),  NEVADA (ITRF00 (1997)-Derived from IGS08 (NEW))

ITRF2000 epoch 1997 coordinates that have been transformed by HTDP software and are now expressed in the newest NAD83(2011, PA11 or MA11) which is based on IGS08 epoch 2005

2) OLD or “offline”

CORS, GARLIC (GARL),  NEVADA  (ITRF00 (1997)-OLD)

These base coordinates were in the older NAD83(CORS) which is based on ITRF2000 epoch 1997

A Jan 2012 Support Note warned that “Trimble reserves the right to remove these stations from the CBS List unannounced, at a later date.” 

Resulting Loss

Users have lost the ability to directly compare Trimble CBS coordinates with the NGS datasheets in either IGS08 or NAD83.  ITRF2000 epoch 1997.  Ideally users could access NGS HTDP software to transform coordinates from one frame to another.  In actuality, regional variations in IGS08 epoch 2005, the of use default versus location-specific velocities, and other unknown variations are make it impossible to replicate the HTDP-derived coordinates listed in the Trimble CBS. 

Spatial-Ed and friends spent much time in the last few months trying every configuration reagin this comparision.  The results were dishearteining. A true comparision of coordintes cannot been obtained with any reference frame with the "NEW" coordinates against NGS absolute or relative antenna positions for any reference frame for tested base stations across the Lower 48 or AK.

Impact

Because GPS and GIS data are in different spatial reference frames,  it is impossible to avoid considering datums when moving combining GPS and GPS data. Since we wish to do the right thing and accuracy matters we are hoping Trimble will shift GPS Pathfinder Office's base from ITRF00 epoch 1997  to a latest NAD83 realizations for North America NAD83(2011), the Pacific NAD83(Pa11) and the Marianas NAD83(MA11).