How do you compute the shift from NAD83(90) to NAD83(2011)?
TIA.
You can look at NSRS stations around where you want to know the shift, and compute a mean shift. There is no way to compute an exact value. This is similar to what NADCON does, although it uses a grid created from the nearby values.
The only way to get "good" NAD83 (2011) values from NAD83 (90) is to readjust.
Thanks John.
Unfortunately, the data for my area doesn't go back that far, by 15 years.
Maybe I'm missing the boat somewhere, but here is my 2-bits:
Short version:
ANY 2005ish observation in excess of 2 hours can be re-processed through OPUS-Static TODAY. ANY shorter duration observations could be post processed again using the IGS08 Orbits currently available for that date (which is what OPUS will use).
I would re-occupy at least TWO of the older stations, and submit those to OPUS_Static.
Put it all together, and pull the LS Trigger, and see what you get.
Loyal
I computed the 7-parameter shift between the two for the State of Louisiana using the coordinates of all CORS sites in the state. With those parameters, it's pretty easy to do a shift between the two reference frames. I presented that to the LSPS at the last annual meeting in Marksville, LA recently.
Can you go back more than to 2005? I have files back to 1999.
Leon
I have re-submitted RINEX files that I collected back in the late 1990s to OPUS_Static (post NAD83[2011]) and found EXCELLENT agreement with solutions using RINEX Files collected in the last couple of years.
The real wildcard is (and ALWAYS IS) the velocity estimates used by HTDP. In my experience here in the Great Basin, these estimates get BETTER with each version of HTDP, and are currently very good.
In order to make this work properly, you MUST use the IGS Absolute Antenna Calibrations in your Post Processing Software, but that should be a given.
Loyal
Howdy,
Have you looked at the NGS tool http://beta.ngs.noaa.gov/GEOCON/ ?
From this page:
GEOCON recognizes as input the NGS Blue Book *80* and *86* position records. The coordinate transformation and the associated quality values are obtained through biquadratic interpolation within a series of grids. Third party applications may obtain identical results if they use the same grids and algorithms.
GEOCON employs high resolution grids (1 arcminute by 1 arcminute) to obtain unprecedented fidelity in modeling coordinate differences. Frequently, one may see that the reported quality is extremely good (e.g. 1 cm or better), but this is not comparable to a geodetic readjustment of survey measurements. The National Geodetic Survey considers actual readjustment of survey measurements, and not coordinate transformations, as best practice.
Cheers,
DMM
Transformations are ALWAYS an average of the differences in coordinates. Thus they are a distant second choice to a re-computation or readjustment.
GEOCON converts from the last HARN re-adjustment for a state to NAD83 (NSRS2007). GEOCON11 converts from NSRS2007 to 2011. They list the HARN re-adjustments in the GEOCON operator's guide. For instance, Florida is listed as NAD83(1999).
