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Chockstone Forum - Crag & Route Beta

Crag & Route Beta

Area Location Sub Location Crag Links
VIC Grampians (General) (General) (General) [ Grampians Guide | Images ] 

Author
Anyone know how to convert GR to lat/long
gfdonc
18/06/2014
1:08:35 PM
Hi,
A lot of the (old?) info around for the Grampians has 6-digit grid references e.g. Blockbuster Buttress at GR 341880.
Anyone know how to convert these to lat/long for GPS? There's a calculator on the Geoscience Australia website but it's looking for more digits and/or additional map reference information.
Tks
Steve

nmonteith
18/06/2014
2:03:56 PM
I think by definition a grid reference is a grid reference to a particular map, so you would certainly need to know that information to convert it. A grid reference is not some sort of universal location system.
kieranl
18/06/2014
2:15:15 PM
The Grampians references are either for the 1:25000 series or the 1:100000 series.

The 1:25000 map uses the Australian Geodetic datum 1966 and I beleve the 1:100000 is based on the 1:25000

I haven't worked out the conversion but this web page might help :

http://www.ga.gov.au/earth-monitoring/geodesy/geodetic-techniques/calculation-methods.html
gnarly_rider
18/06/2014
2:33:07 PM
>>? There's a calculator on the Geoscience Australia website but it's looking for more digits and/or additional map reference information.

You are correct:

1/. These numbers are an abbreviated version of the full Eastings and Northings (6 and 7 digits respectively, in metres), and

2/. You will also need to know the Projection in which these coordinates have been measured, which will be a function of the year they were provided. The 3 most recent Projections were AGD66, AGD84 and GDA94, the last 2 digits (obviously) representing the year that projection was created (and generally was then used in preference to the previous projections. So if the map/booklet your GR numbers have coem from was circa 1990, most likely the GR values are using AGD84

3/. You will also need to know the UTM zone within these projections: the Grampians in I think in zone 54, whilst Melbourne is on Zone 55.

To flesh out the GR numbers, as an example Halls Gap in AGD84 (Zone 54) has coordinates of approx 634200E 5887400N, which I think would equate to GR 342 874. IE (I am rusty) I think GR numbers represent multiples of hundreds of metres.
widewetandslippery
18/06/2014
2:40:45 PM
I use the same version of equation as above.

NB: i get lost a lot...................
gnarly_rider
18/06/2014
2:47:01 PM
Whew, my rustiness is not as bad as I thought!

http://www.diamondspirit.net/adunk/MapsAndDatums.html

So GR 341880 should equate to 634100E and 5888000N, but you will need to double check the Projection, as previously stated.

Grinder
18/06/2014
2:54:28 PM
The easiest way is to get a copy of the original 1:25,000 VICmap. The six-digit GR (three digit Easting followed by three digit Northing) is an abbreviation of a much longer GR which will be on any map of the area. However, my understanding is that the grid used for Victoria changed in 2000 from AGD66 to GDA94 so you probably need a map of the area printed before then.

I don't have such a map handy, but I'm sure another chockstoner will.How many digits do you need for the calculator? The map should provide at least another two digits for each of the easting and northing. The extra digits will apply to all the other GR's you have.



martym
18/06/2014
2:55:18 PM
Hmm. I tried those coordinates in Google Maps & got Dujian Mountain in Tibet.

Looks cool - have fun!

mallion
18/06/2014
3:16:14 PM
On 18/06/2014 gnarly_rider wrote:
>
>2/. You will also need to know the Projection in which these coordinates
>have been measured, which will be a function of the year they were provided.
>The 3 most recent Projections were AGD66, AGD84 and GDA94, the last 2 digits
>(obviously) representing the year that projection was created (and generally
>was then used in preference to the previous projections. So if the map/booklet
>your GR numbers have coem from was circa 1990, most likely the GR values
>are using AGD84
>

All good, but AGD66, AGD84 and GDA94 are not projections they are just coordinate systems.
gfdonc
18/06/2014
4:23:33 PM
Thanks all. I'll investigate further based on these suggestions.

Gnarly, I punched in the numbers you suggested, and ended up at -37.144774, 142.509967, which is certainly in the right area (east of Halls Gap). I'll need to check against some known references.
kieranl
18/06/2014
5:13:19 PM
From my Halls Gap 1:25000 map I read the summit of Bellfield peak as 6347 (e) 58856 (n) , which is shown in the Baxter guide as GR 347856.

Punched into the Redfearns calculator spreadsheet that I downloaded from ga.gov.au (zone 54, east 634700.00, north 5885600.00) gave 37 09 58 E 142 30 57 N which is fairly close to a GR that I've got for the top of Rolling Thunder which is a bit south of the summit.

(edited for consistency with guidebook)
Mr Poopypants
18/06/2014
6:17:13 PM
Probably much easier to change the settings in your GPS to the correct map datum for the grid references. Then you can just punch in the grid refs you have and it'll take you there.
The biggest mistake most people seem to make with GPS is to not set the unit to the map datum for the map you are using. Get a copy of the map, the map datum will be on it.
I've got an ancient first gen. Garmin and even it can be set to all the map datums for Oz.
G.

Duang Daunk
18/06/2014
7:49:02 PM
>Anyone know how to convert GR to lat/long

Joe Grollo does.
argos44
19/06/2014
6:48:34 AM
Mr Poopy hit the nail on the head. Just use your GPS to convert between different position formats. Just make sure the map datum is correct as that is another variable.

There are 14 messages in this topic.

 

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