Q: Ellipsoid conversions, Molodensky constants, etc.

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2 total messages Started by Kevin Sahr Fri, 29 Jul 1994 02:54

#67

Author: Kevin Sahr
Date: Fri, 29 Jul 1994 02:54

11 lines
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I am looking for references, algorithms, code, etc. to perform
coordinate conversions between ellipsoids. I've heard this
referred to as the "datum shift" problem, and have heard
Molodensky constants mentioned in this regard (though I have
no idea what these are). I'd appreciate it if someone could
point me in the right direction.

Thanks!

Kevin
sahr@piglet.uccs.edu

Re: Q: Ellipsoid conversions, Molodensky constants, etc.

#68

Author: gie
Date: Fri, 29 Jul 1994 14:03

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2140 bytes

In article <319r08$qf8@harpo.uccs.edu> sahr@piglet.uccs.edu (Kevin Sahr) writes:
>I am looking for references, algorithms, code, etc. to perform
>coordinate conversions between ellipsoids. I've heard this
>referred to as the "datum shift" problem, and have heard
>Molodensky constants mentioned in this regard (though I have
>no idea what these are). I'd appreciate it if someone could
>point me in the right direction.
>
>Thanks!
>
>Kevin
>sahr@piglet.uccs.edu

Molodensky's method of datum conversion is one of about three major methods.
The others are polynomial corrections and tabular or grid corrections.
What is available will depend upon what area you are involved with.
For the U.S., the preferred and most accurate method is the NADCON
tables as used by the *nad2nad* program distributed with the PROJ.4
system on charon.er.usgs.gov (128.128.40.24).

Secondly, datum conversion is not simply a "conversion between ellipsoids"
but a shift of locations.  In theory, the same ellipsoid could be
used for either datum.

I do have Molodensky factors for global regions but these are not
verified by second source.  Contact me direct if you need to pursue
these.

Gerald (Jerry) I. Evenden   Internet: gie@charon.er.usgs.gov
voice: (508)563-6766          Postal: P.O. Box 1027
  fax: (508)457-2310                  N.Falmouth, MA 02556-1027

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