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 Post subject: NAD27 to NAD83 conversion
PostPosted: February 20th, 2012, 3:17 pm 
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Joined: August 5th, 2002, 7:00 pm
Posts: 145
Location: Montreal, Quebec Canada
Hello,
for some mapping activity, and eventual automated generation of canoe maps, i have the following problem:
- i have locations that are lon-lat, in NAD27
- i want their equivalent, in NAD83

The several geography experts i have asked all answered me... easy, you enter these parameters into ArcGis, and you will have the answer.

I want to solve the problem separately from ArcGis, to embed into my own software and tools.
For those interested, I have an XSL transform calling java code, and from that java code i want to know the answer.

The various experts told me... "nahh, there is no formula". But i am telling myself, if a software program, there is for sure an algorithm, formula, or tables somewhere...

The only method i have found so far is to query (from my java program) the following URL:
http://www.geod.nrcan.gc.ca/apps/ntv2/ntv2_geo_f.php, with the appropriate parameters, and then analyze the response to extract the answer.

Any help with this would be much appreciated

Thanks,

Charles


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 Post subject: Re: NAD27 to NAD83 conversion
PostPosted: February 21st, 2012, 3:04 pm 
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Joined: June 20th, 2001, 7:00 pm
Posts: 494
Location: South Frontenac Twsp., ON
YES! ... There is a formula to convert coordinates, either Geographics or UTM's between NAD27 & NAD83.

Go to the NRCan website below and do a Contact Us and describe what you are looking for ....

'A Transformation Modelling Software that will convert coordinates between NAD27 and NAD83 anywhere in the Canadian landmass'

http://www.nrcan.gc.ca/earth-sciences/p ... data/11645

I am retired now, but one of the last projects that I worked on was the NAD27 > NAD83 Adjustment of Canadian Topographic Mapping and the Transformation Model I described above.

I no longer have a contact there, however the product should be available and most likely freely.

Let me know if you don't get the help you need and I'll see what I can do.


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 Post subject: Re: NAD27 to NAD83 conversion
PostPosted: March 28th, 2012, 4:05 pm 
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Joined: October 20th, 2003, 9:20 pm
Posts: 221
Location: Ottawa
The math that does the conversion is known as the Molodensky Transform. If you Google that, you will find some source code examples (such as here: http://home.hiwaay.net/~taylorc/bookshe ... olodensky/).

Note that there are more complex functions that give more accurate results out there, but I have it on good authority that consumer GPS and mapping products only use the Molodensky ("good enough for government work"!)

HTH

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 Post subject: Re: NAD27 to NAD83 conversion
PostPosted: March 29th, 2012, 8:14 am 
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Joined: August 5th, 2002, 7:00 pm
Posts: 145
Location: Montreal, Quebec Canada
Exactly the information i was looking for...
Have not tried it yet, should be a couple days/weeks before i do, but definitely i will.

Thanks !!!

Charles


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 Post subject: Re: NAD27 to NAD83 conversion
PostPosted: March 29th, 2012, 12:05 pm 
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Joined: October 20th, 2003, 9:20 pm
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Location: Ottawa
Let us know how you get on!

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