Discussion:
EGM96 to NAVD88 conversion
(too old to reply)
Bill Carson
2004-05-14 17:40:01 UTC
Permalink
I want to convert, if necessary, elevations given relative to the WGS84
EGM96 geoid
to elevations referenced to NAVD88. Because I am not sure what reference
geoid, if any,
that NAVD88 uses, I'm not quite sure where to start. Are NAVD88 elevations
referenced
to any geoid model?

If there is any way to convert between these two datums, I am all ears.

Thanks,

Bill
Giles Evans
2004-05-16 06:49:50 UTC
Permalink
http://crunch.tec.army.mil/software/corpscon/corpscon.html
--
"A Microsoft Certified Systems Engineer is to computing what a McDonald's
Certified Food Specialist is to fine cuisine."
-Giles Evans, MCSE
Post by Bill Carson
I want to convert, if necessary, elevations given relative to the WGS84
EGM96 geoid
to elevations referenced to NAVD88. Because I am not sure what reference
geoid, if any,
that NAVD88 uses, I'm not quite sure where to start. Are NAVD88 elevations
referenced
to any geoid model?
If there is any way to convert between these two datums, I am all ears.
Thanks,
Bill
Bill Carson
2004-05-16 18:09:58 UTC
Permalink
Post by Giles Evans
http://crunch.tec.army.mil/software/corpscon/corpscon.html
Thanks for the link, it has been awhile since I looked at Corpscon, but I
don't
think it will do what I need. I am downloading it now and will play with it
to
see if can convert EGM96 heights to NAVD88. But, I don't think it can
because EGM96 and Geoid96 are not the same. EGM96 is a global geoid
model and Geoid96 is specifically for the USA.

The other problem is that I don't beleive NAVD88 is actually referenced to a
geoid, so it would require more than a transformation to convert EGM96 to
NAVD88.

Thanks,

Bill
C.M.German
2004-05-16 19:17:41 UTC
Permalink
Googleing gave me this.......

http://www.ngs.noaa.gov/PUBS_LIB/gislis96.html

Maybe it will help you.


Cm
Post by Bill Carson
Post by Giles Evans
http://crunch.tec.army.mil/software/corpscon/corpscon.html
Thanks for the link, it has been awhile since I looked at Corpscon, but I
don't
think it will do what I need. I am downloading it now and will play with it
to
see if can convert EGM96 heights to NAVD88. But, I don't think it can
because EGM96 and Geoid96 are not the same. EGM96 is a global geoid
model and Geoid96 is specifically for the USA.
The other problem is that I don't beleive NAVD88 is actually referenced to a
geoid, so it would require more than a transformation to convert EGM96 to
NAVD88.
Thanks,
Bill
Bill Carson
2004-05-17 00:40:12 UTC
Permalink
Post by C.M.German
Googleing gave me this.......
http://www.ngs.noaa.gov/PUBS_LIB/gislis96.html
Maybe it will help you.
Thanks, I had already read that one, it is good but it primarily refers
to Geoid96 which, although based somewhat on EGM96, is not the
same. Figure 3 in that article does show a mean offset of NAVD88
with a global geoid model, but I am uncertain which global geoid it
refers to. It might be EGM96 given a discussion of the Rapp(1996)
article found here:
http://www.ngs.noaa.gov/PUBS_LIB/egm96.html

EGM96 is a global geoid that uses the WGS84 ellipsoid as a
horizontal datum. See:
http://cddisa.gsfc.nasa.gov/926/egm96/egm96.html
A good discussion of EGM96 can also be found in the DOD WGS84
documentation here:
ftp://164.214.2.65/pub/gig/tr8350.2/wgs84fin.pdf

From the GEOID96 FAQs found at this page:
http://www.ngs.noaa.gov/GEOID/GEOID96/faq.html
"Our current estimate of the NAVD 88 vertical datum offset is 31.4 cm below
the current best estimate of the Earth's best-fit global geopotential. (A
piece of
good news: the NAVD88 offset seems to be a constant offset; the same
throughout the conterminous United States.) "
But, again I don't know what global datum they are referring to.

As far as I understand it, NAVD88 is not referenced to an earth centered
geoid datum, which makes it more difficult to relate to other datums that
are.
I suspect there is no easy conversion between EGM96 heights and NAVD88,
but the paper you found is good for understanding how you might go about
it. But, I don't want to reinvent the wheel, especially since I am no expert
in
the subject

Thanks,

BIll
C.M.German
2004-05-17 11:44:02 UTC
Permalink
It's sort of like the problem I have here of explaining to people that "high
tide" is not the same elevation everywhere in the county!
Post by Bill Carson
Post by C.M.German
Googleing gave me this.......
http://www.ngs.noaa.gov/PUBS_LIB/gislis96.html
Maybe it will help you.
Thanks, I had already read that one, it is good but it primarily refers
to Geoid96 which, although based somewhat on EGM96, is not the
same. Figure 3 in that article does show a mean offset of NAVD88
with a global geoid model, but I am uncertain which global geoid it
refers to. It might be EGM96 given a discussion of the Rapp(1996)
http://www.ngs.noaa.gov/PUBS_LIB/egm96.html
EGM96 is a global geoid that uses the WGS84 ellipsoid as a
http://cddisa.gsfc.nasa.gov/926/egm96/egm96.html
A good discussion of EGM96 can also be found in the DOD WGS84
ftp://164.214.2.65/pub/gig/tr8350.2/wgs84fin.pdf
http://www.ngs.noaa.gov/GEOID/GEOID96/faq.html
"Our current estimate of the NAVD 88 vertical datum offset is 31.4 cm below
the current best estimate of the Earth's best-fit global geopotential. (A
piece of
good news: the NAVD88 offset seems to be a constant offset; the same
throughout the conterminous United States.) "
But, again I don't know what global datum they are referring to.
As far as I understand it, NAVD88 is not referenced to an earth centered
geoid datum, which makes it more difficult to relate to other datums that
are.
I suspect there is no easy conversion between EGM96 heights and NAVD88,
but the paper you found is good for understanding how you might go about
it. But, I don't want to reinvent the wheel, especially since I am no expert
in
the subject
Thanks,
BIll
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