How accurate is the HTDP tool from NGS for reference frame transformations (as opposed to accounting for coordinate changes with time). I don't have any specific project in mind, just general interest. I would mainly be interested in up-to-date reference frames. Would it be safe to think that the transformations would be accurate to a millimeter, which is usually better than accuracy you would find on a good NGS data sheet for NAD83 coordinates? In other words, can I neglect the accuracy of the tool and just worry about the accuracy of the input?
The HTDP tool incorporates officially adopted transformation parameters. You can sort through the source file (a FORTRAN file included in the download) to find the actual values used. Be sure to take care with significant figures. As with the Lat/Lon to SPC coordinate transformations, just because values are shown to the fifth-decimal place and millimeter. respectively, this should not be assumed to mean the values are that accurate.
The transformation parameters between ITRF/IGS iterations are those officially adopted by the IERS. A web search will readily yield the documentation regarding these parameters. The IERS conventions are available for free download as PDF files. Interesting reading.
The ASCE published a book on OPUS (not free): CORS and OPUS for Engineers, edited by Tomas Soler (2011) which has a detailed article on HTDP, as well as articles on transformation between NAD83 and ITRF and transforming OPUS results to WGS84.
Check the NGS site for articles on HTDP; many are free, some not.
HTH,
DMM
I don't know if this is exactly what you're looking for but have you tried the Geocon11 and Geocon tools on the NGS site? Geocon11 is a transformation between NAD83(2011) and NAD83(NSRS 2007); Geocon is a transformation between NAD83(NSRS 2007) and NAD83(HARN). I've used them both to take NAD83(2011) 2010.00 coordinates "back in time" and vice versa, they seem to be pretty good.
GeeOddMike, post: 329264, member: 677 wrote: transformation between NAD83 and ITRF and transforming OPUS results to WGS84
Stupid question time... I thought that the current IGS08, ITRF, and WGS84 datums were pretty much aligned with one another?
Lee D, post: 329265, member: 7971 wrote: I don't know if this is exactly what you're looking for but have you tried the Geocon11 and Geocon tools on the NGS site? Geocon11 is a transformation between NAD83(2011) and NAD83(NSRS 2007); Geocon is a transformation between NAD83(NSRS 2007) and NAD83(HARN). I've used them both to take NAD83(2011) 2010.00 coordinates "back in time" and vice versa, they seem to be pretty good.
I'm mostly interested in transforming between the ITRF or WGS framework and the NAD83 framework. HTDP is the only tool I know of that does this.
Lee D, post: 329267, member: 7971 wrote: Stupid question time... I thought that the current IGS08, ITRF, and WGS84 datums were pretty much aligned with one another?
I interpreted the question to be about the general issue of transformations and not on this specific issue. My point was/is that the transformations in the HTDP program use the "official" parameters. The methodology used in applying these parameters (transformations, rotations, scale and their velocities) is the use of rotation matrices.
An excellent reference is: http://www.iers.org/IERS/EN/Publications/TechnicalNotes/tn32.html?nn=94912
On the issue of ITRF and WGS see: ftp://itrf.ensg.ign.fr/pub/itrf/WGS84.TXT
While the latest versions of NAD83 and ITRF have well-defined transformation parameters, the issue of WGS 84 remains separate. My understanding of NGA policy is that they will maintain WGS to be compatible with the current version of ITRF within 5 centimeters. Some interesting papers are available about how NGA "validates" their coordinates.
There is the well-known difference (>2 meters) between the origins of ITRF and NAD83 requiring translations. NGS generates the transformation parameters between NAD83 and ITRF and updates them as the two frames are improved.
Using my iPAD or would have provided the actual values (on my computer).
HTH, DMM
