NGS releases revised coordinates for all CORS sites…

On September 6, 2011 NGS’s CORS group released revised coordinates for all CORS sites. The new coordinates update both the global frame and the National Spatial Reference Frame as follows.

New Frames Previous Frames
IGS08 Epoch 2005.00 ITRF00 Epoch 1997.00
NAD 83(2011) Epoch 2010.00 NAD 83(CORS96) Epoch 2002.00
NAD 83(MA11) Epoch 2010.00 NAD 83(MARP00) Epoch 2002.00
NAD 83(PA11) Epoch 2010.00 NAD 83(PACP00) Epoch 2002.00

NGS is in the process of completing an adjustment of the passive control network. Until the adjustment is complete, OPUS will allow users to choose getting coordinates in either the new or previous reference frames. Once the passive network is adjusted to NAD 83(2011, MA11, PA11) then the OPUS support for ITRF00 and NAD 83(CORS96, MARP00, PACP00) will end.

Q: Which button/reference frame should I choose to get my solution?
A: Most users should start using the new reference frame, especially for users who are only interested in the global reference frame i.e. IGS08. Users who are in the middle of a project, will probably want to continue using their original reference frame.

Q: How much will OPUS coordinates change if I use the new reference frame?
A: The biggest changes in the coordinates are caused by the change from relative to absolute antenna calibrations and the change in reference epoch as defined at the top of this page. OPUS coordinate changes should mimic those of the CORS namely: Difference of NAD 83(2011) epoch 2010.00 minus NAD 83(CORS96) epoch 2002.00: mean East 0.05±5.25 cm; North 2.12±6.08 cm; Up -0.66±2.24cm and median values of: East -0.12 cm; North 0.00 cm; Vertical -0.80 cm. For maps showing differences in CORS coordinates see this FAQ.

Q: Has the OPUS processor changed?
A: No. The OPUS processor simply points to the new set of CORS coordinates and absolute antenna calibrations.

Q: Is GEOID09 compatible with solutions obtained using the new coordinates?

A: More or less. The GEOID09 model was built from CORS96-derived ellipsoid heights, therefore orthometric heights obtained will differ by at least the change in ellipsoid height. If orthmetric heights are critical to your needs, we recommend that you submit a solution through both submission buttons and evaluate the differences. Shortly after the completion of the passive adjustment a new geoid will be created using the consistent set of new ellipsoid coordinates from both CORS and passive control.

Q: Will OPUS published solutions use the new or old reference frames?
A: OPUS published solutions will be in whichever reference frame you selected to get a solution in. Once the passive adjustment is completed and OPUS no longer supports the old coordinates, all published solutions with old coordinates will be updated to the new reference frames, with the old coordinates retained as superseded values.

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