Conversion between NAD83(CSRS) to WGS-84

Discussion in 'General GPS Discussion' started by gpsabove, Sep 14, 2006.

  1. gpsabove

    gpsabove Guest

    Hi there,

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

    Thanks.

    Johnson
     
    gpsabove, Sep 14, 2006
    #1
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  2. gpsabove

    Sam Wormley Guest


    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
     
    Sam Wormley, Sep 14, 2006
    #2
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  3. gpsabove

    gpsabove Guest

    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


     
    gpsabove, Sep 14, 2006
    #3
  4. gpsabove

    Sam Wormley Guest

    Try: http://www.posc.org/Epicentre.2_2/DataModel/ExamplesofUsage/eu_cs.html
     
    Sam Wormley, Sep 14, 2006
    #4
  5. 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
     
    Eino Uikkanen, Sep 14, 2006
    #5
  6. 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).
     
    Eino Uikkanen, Sep 14, 2006
    #6
  7. gpsabove

    Chuck Taylor Guest


    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.
     
    Chuck Taylor, Sep 14, 2006
    #7
  8. gpsabove

    sat_alight Guest

    WGS-84(G1150) differs from NAD83(CORS96) by up to 2 meters depending on
    where you are in the US.
     
    sat_alight, Sep 16, 2006
    #8
  9. 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
     
    Eino Uikkanen, Sep 16, 2006
    #9
  10. 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
     
    Wolfgang S. Rupprecht, Sep 16, 2006
    #10
  11. gpsabove

    Paul Hirose Guest

    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
     
    Paul Hirose, Sep 17, 2006
    #11
  12. gpsabove

    Jack Yeazel Guest

    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
     
    Jack Yeazel, Sep 18, 2006
    #12
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