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Anonymous via the Cypherp science forum beginner
Joined: 20 Jun 2005
Posts: 17

Posted: Tue Jul 18, 2006 7:45 pm Post subject:
Converting coordinates from one datum to an other?



Is there a simple formula to convert a lat/long set of
coordinates from one geodetic datum to another (such as the
Hayford International to the 80/84 Worldwide Datum)? 

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jimirwin science forum beginner
Joined: 19 Jul 2006
Posts: 1

Posted: Wed Jul 19, 2006 12:40 pm Post subject:
Re: Converting coordinates from one datum to an other?



Anonymous via the Cypherpunks Tonga Remailer <nobody@cypherpunks.to> wrote
in news:20060718194512.27749170B6@mail.cypherpunks.to:
Quote:  Is there a simple formula to convert a lat/long set of
coordinates from one geodetic datum to another (such as the
Hayford International to the 80/84 Worldwide Datum)?

Search for Molodensky Transformation and/or Helmert Transformation.

Jim Irwin
http://www.holoscenes.com 

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Eino Uikkanen science forum beginner
Joined: 26 Jun 2006
Posts: 2


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Anonyma science forum beginner
Joined: 03 Jun 2006
Posts: 3

Posted: Thu Jul 20, 2006 5:46 pm Post subject:
Re: Converting coordinates from one datum to an other?



jimirwin wrote:
Quote:  Anonymous via the Cypherpunks Tonga Remailer <nobody@cypherpunks.to
wrote in news:20060718194512.27749170B6@mail.cypherpunks.to:
Is there a simple formula to convert a lat/long set of
coordinates from one geodetic datum to another (such as the
Hayford International to the 80/84 Worldwide Datum)?
Search for Molodensky Transformation and/or Helmert Transformation.

Thanks, I think Iv'e found a good one: http://www.colorado.edu/geography/gcraft/notes/datum/gif/molodens.gif
I also found an online calculator: http://www.ngs.noaa.gov/cgibin/nadcon.prl
I tried Peter Dana's version of Molodensky's formula and his example and
it works. I then tried it on NADCON and got slightly different answers,
30.0002238973/100.0003696013/0m, 30.0002238891/100.0003695878/232m (Dana)
and 30.0002112611/100.0003501667 (NADCON). So changing the height
doesn't change it much.
So I then tried different longitudes based on a latitude of 40:
latitude longitude
NAD27: 40.0000000000 65.0000000000
Dana: 39.9999643708 64.9992930771
NADCON: 40.0001671027 64.9992685694
40.0000000000 70.0000000000
39.9999915613 69.9994472150
40.0001355250 69.9994378722
40.0000000000 80.0000000000
40.0000255521 79.9997669068
40.0000737694 79.9997744055
40.0000000000 90.0000000000
40.0000315820 90.0000936811
40.0000484805 90.0001139222
40.0000000000 100.0000000000
40.0000094676 100.0004176089
40.0000058944 100.0004058361
40.0000000000 110.0000000000
39.9999598811 110.0007288478
39.9999636277 110.0007048388
40.0000000000 120.0000000000
39.9998843289 120.0010179411
39.9999048055 120.0010352250
40.0000000000 130.0000000000
39.9997851067 130.0012761048
39.9998735527 130.0013791138
I understand these use different methods and NADCON uses actual recorded
data values in its calculation, so it is probably more accurate.
But Dsna's formula is probably simpler.
The next question is is there a formula for finding Deltas X, Y and Z,
perhaps a way to make them variables, thereby increasing the accuracy at
the global level?
If not, is there a table somewheres that gives the different values
between the different datums? 

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David L. Wilson science forum beginner
Joined: 31 May 2005
Posts: 37

Posted: Fri Jul 21, 2006 12:16 am Post subject:
Re: Converting coordinates from one datum to an other?



"Anonyma" <anonbounces@deuxpi.ca> wrote in message
news:313fbc1b6c8289c8f8941960ea2faca8@deuxpi.ca...
Quote:  jimirwin wrote:
Anonymous via the Cypherpunks Tonga Remailer <nobody@cypherpunks.to
wrote in news:20060718194512.27749170B6@mail.cypherpunks.to:
Is there a simple formula to convert a lat/long set of
coordinates from one geodetic datum to another (such as the
Hayford International to the 80/84 Worldwide Datum)?
Search for Molodensky Transformation and/or Helmert Transformation.
Thanks, I think Iv'e found a good one:
http://www.colorado.edu/geography/gcraft/notes/datum/gif/molodens.gif
I also found an online calculator:
http://www.ngs.noaa.gov/cgibin/nadcon.prl
I tried Peter Dana's version of Molodensky's formula and his example and
it works. I then tried it on NADCON and got slightly different answers,
....
I understand these use different methods and NADCON uses actual recorded
data values in its calculation, so it is probably more accurate.
But Dana's formula is probably simpler.

There is a subtle point here. NADCON is the US legal conversion
standard even though it is based on certainly some mismeasured points. So
you need to define what is meant when you say accurate. If you think about
it, they needed to do that as one does not want to be arguing old property
line.
But generally the only recommeded accurate way to locate a point in one
system is to measure it in that system. If converted to another system, it
is best to state which transformation was used.
You should also get the following 2 excellent pieces of software
CORPSCON (a windows implementation of NADCON)
http://crunch.tec.army.mil/software/corpscon/corpscon.html
and GEOTRANS.
http://earthinfo.nga.mil/GandG/geotrans/index.html
Quote:  The next question is is there a formula for finding Deltas X, Y and Z,
perhaps a way to make them variables, thereby increasing the accuracy at
the global level?
If not, is there a table somewheres that gives the different values
between the different datums?

There certainly are talbles of the deltas. Run, do not walk to the following
websites
http://earthinfo.nga.mil/GandG/coordsys/csat_pubs.html
http://earthinfo.nga.mil/GandG/coordsys/datums/index.html
But keep in mind that these should be take as approximations. In addition
there is some ambiquity in some of the definitions. Through on top of that
that land masses driftand by different amounts so things are time
dependent transformations in some cases.
Make sure you read the red at
http://earthinfo.nga.mil/GandG/coordsys/datums/notice_8142002.html 

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David L. Wilson science forum beginner
Joined: 31 May 2005
Posts: 37


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