Conversion between NAD83(CSRS) to WGS-84

Hi there,

I am looking for a formula to convert coordinates from NAD83 to WGS84.
Could anybody help?

Thanks.

Johnson

 

NGS Geodetic Tool Kit - On-line interactive computation of geodetic values
http://www.ngs.noaa.gov/TOOLS

Geodetic Software (Free for PC from NGS)
http://www.ngs.noaa.gov/PC_PROD/pc_prod.shtml

Coordinate and Datum Transformations from Chuck Taylor
http://home.hiwaay.net/~taylorc/toolbox/geodesy/datumtrans/

Datum Conversion Software Comments from David L. Wilson
http://users.erols.com/dlwilson/gpsfaq.htm

Aviation [Navigation] Formulary V1.43 by Ed Williams
http://williams.best.vwh.net/avform.htm

 

Thank you very much, Sam,

I checked the links, and it seemed that HTDP could do the conversion.
However, no formula was provided.

I saw the conversion between NAD27 and WGS84, but no formula for NAD83
to WGS84 DIRECTLY.

I was looking for the formula and parameters to write up a program. Do
you know where I can find them?

Johnson

 

Try: http://www.posc.org/Epicentre.2_2/DataModel/ExamplesofUsage/eu_cs.html

 

You can use my freeware GeoConv to convert between datums like NAD83 and
WGS84:
http://www.kolumbus.fi/eino.uikkanen/geoconvgb/index.htm

However, since NAD83 and WGS84 are so close to each other, you don't need
any conversion tools or formulae in this case; just consider NAD83 and WGS84
equal (at least for navigation and positioning)

Eino Uikkanen
http://www.kolumbus.fi/eino.uikkanen/gb/index.htm

 

I checked more, because I didn't regard the CSRS in NAD83(CSRS); below a cut
from http://www.geod.nrcan.gc.ca/faq_e.php . However, for most purposes you
still could consider NAD83(CSRS) and WGS84 equal.

Eino Uikkanen
http://www.kolumbus.fi/eino.uikkanen/gb/index.htm


What is the difference between NAD83 and WGS84?

In the beginning (1980s), WGS84 was based on the same Doppler reference
frame as NAD83. Both reference systems were therefore compatible with each
other, at least to the accuracy of the Doppler reference frame (about a
meter).

On Jan 2, 1994, a new realization called WGS84(G730) was introduced. This
version was derived from the International Terrestrial Reference Frame
ITRF91. This was the point at which WGS84 was no longer compatible with
NAD83. The offset was about 2 m at the origin (there was also a significant
misalignment of the axes). The total difference in Canada amounts to about
1.5 m.

Later, on Sep 29, 1996, another realization called WGS84(G873) was
introduced. It was derived from the more accurate ITRF94. Finally, in Jan
2002, WGS84 was once again updated. This time it was derived from the even
more accurate and stable ITRF2000. This current one is called WGS84(G1150).

 

The differences between NAD83 and WGS84 are chiefly the result of
movement of the Earth's crust. Consequently the differences are small
and vary with time. The relatively simple 3- and 7-parameter formulas
commonly used for transforming points between other pairs of datums
lack the necessary accuracy for a NAD83-to-WGS84 transformation.

I'd suggest using the HTDP source as a starting point for your
program.

 

WGS-84(G1150) differs from NAD83(CORS96) by up to 2 meters depending on
where you are in the US.

 

Yes, I knew that, but 2 meters is less than the average _residual error_ in
many 3D-similarity transformations between older datums and WGS84. Therefore
I said, that we could consider NAD83 and
WGS84 equal at least for navigation and positioning. If one needs a
conversion between WGS-84(G1150) and NAD83(CORS96), that gives smaller
residual errors, he needs to use more accurate transformation methods or
calculate transformation parameters for a small area. He also needs accurate
tools to get most accurate WGS84 reference (geodetic application accuracy).

It would be interested to know, where this accurate conversion is needed and
where the accurate WGS84 reference is got. Maybe a geodetic application?
Maybe the original poster can tell us that.

Eino Uikkanen
http://www.kolumbus.fi/eino.uikkanen/gb/index.htm

 

USGS has 30 cm per pixel overhead imagery for some parts of the US
(such as the SF Bay area). Having a 2 meter error in the conversion
from the GPS's native WGS84 to the USGS's NAD83 should be noticeable
(but in practice, I honestly can't tell). So far I've just been using
the "unity transform" and it sure seems good enough, but perhaps if I
had both registrations to compare to each other I'd see a difference.

-wolfgang

 

Since WGS84 is now extremely close to the ITRF, this ITRF -> NAD83
transformation may be adequate. You would have to reverse the sense of
the formula, though.

http://www.ngs.noaa.gov/CORS/Coords.html

 

We have a GPS reference station for the county near our
house in NAD-83 coordinates where we do our accuracy
testing...

Averaging a GPS position for about an hour will detect the
difference in the GPS's averaged coordinates (WGS-84) and
the published NAD-83 coordinates (about 0.8m here in
Atlanta)...

See: http://www.gpsinformation.net/main/ngs-accuracy.txt