Map co-ordinates Lat/Long to WGS84....

Submitted: Thursday, May 03, 2007 at 11:38
ThreadID: 45045 Views:14143 Replies:4 FollowUps:5
This Thread has been Archived
Being an old salt from years past I have always navigated at sea in lat-long however as we all know land charts are now commonly issued in AGD - to conform with the WGS84 system.

Is there an easy conversion formula from the old to the new as some paper charts I have are in the old system and some of the newer versions are obviously different.

This poor old brain needs a bit of help please?
Back Expand Un-Read 0 Moderator

Reply By: Robin - Thursday, May 03, 2007 at 12:16

Thursday, May 03, 2007 at 12:16
Hi John

Not aware of a real easy system - one can use complex formulas on a calculator.

A way is to mark a point on you long/lat map and then use the advantage of AGD (UTM) which reads out in meters to move across your map according to its scale/

Great trick in the field is to bang a waypoint into a gps and then go to setup and change to your required datum.

Robin Miller
Robin Miller

Member
My Profile  Send Message

AnswerID: 237637

Follow Up By: Robin - Thursday, May 03, 2007 at 12:40

Thursday, May 03, 2007 at 12:40
Forgot - similarly at home , bang waypoints into one of the many free gps programs and change datum.

Someone may also remember tag for a so constructed XL spreadsheet that did this
Robin Miller

Member
My Profile  Send Message

0
FollowupID: 498692

Follow Up By: The Explorer - Thursday, May 03, 2007 at 12:49

Thursday, May 03, 2007 at 12:49
You are both confusing the terminology (which is not good with a subject that can be confusing enough)

AGD doesnt = UTM nor does it "conform" with WGS84 .

In simple terms (AFAIK)
Latitude/longitude and UTM (Universal Transverse Mercator) are terms that refer to the coordinate system being used i.e Degrees, minutes, seconds (for lat/long) or metres (UTM).

WGS84, AGD84, GDA94 etc are datums i.e. reference points within the earth from which the coordinate systems are measured/originate from. You can use any datum with any coordinate system, as long as you let people know what datum you are using when you pass the coords on.

Today, in Australia, GDA is used as the datum when creating new maps (well it should be). The GDA94 datum closely approximates WGS84 and both can be considered equal for navigation purposes. Maps that utilise GDA datum and UTM produce a coordinate grid referred to as the Map Grid of Australia (MGA). Prior to that Australian maps were produced using the AGD84 (or 66) datum. Maps that utilise AGD and UTM produce a coordinate grid referred to as the Australian Map Grid (AMG). There are still many maps sold using the older AGD84 or 66 system which can of course cause problems as there is a difference of about 200metres between coordinates numbers created using AGD and GDA.

John – its is unclear from your original post whether you want to convert WGS84 coords to AGD (though I suspect you mean GDA, in which case no conversion is required) or if you wish to convert lat/long (degrees etc) coords to UTM (metres) coords…..or both??

Cheers
Greg
I sent one final shout after him to stick to the track, to which he replied “All right,” That was the last ever seen of Gibson - E Giles 23 April 1874

Lifetime Member
My Profile  My Blog  Send Message
Moderator

0
FollowupID: 498693

Reply By: Member - John L G - Thursday, May 03, 2007 at 13:00

Thursday, May 03, 2007 at 13:00
Robin & Greg

My main problem, apart from all the ones my partner keeps reminding me of and which seem unfixable at my age, are that my trusty MLR SP24 gps happily gives me co-ordinates in Lat & Long but of course if I am using a local 4WD map or newer version chart as distinct from my old paper charts which I have had for years, I find myself looking at map co-ordinates that are a bit of a mystery to me.

Spent an hour scrolling thru the GPS menu but am unsure how to get it to give me the Co-ordinates in the new configuration. The manual would probably help if I had one but had it a few years now and no idea where it is.

So clueless in the bush may best describe me....

AnswerID: 237641

Follow Up By: Robin - Thursday, May 03, 2007 at 13:20

Thursday, May 03, 2007 at 13:20
Hi John

Agree totally with Greg , and probably should have been clearer myself.
The methods I described works for both co-ord and datums.

But we probably should add that the datum conversion issue is a minor adjustment usually 100 whatever meters , co-ord conversion between lat/lon and UTM is between degrees and meters .

Hopefully someone here can help with your specific GPS , usually to change either is under a setup menu sometimes called navigation

Robin Miller
Robin Miller

Member
My Profile  Send Message

0
FollowupID: 498701

Follow Up By: The Explorer - Thursday, May 03, 2007 at 13:25

Thursday, May 03, 2007 at 13:25
It may not be this simple...but if you want to get UTM coords on your screen

To set the coordinate format

Press the Page button on your GPS receiver until the Menu screen appears.
Select System Setup.
Select Coordinate System.
Select UTM from List.

I dont know what datum the maps you have are...but

To set the datum

Press the Page button on your GPS receiver until the Menu screen appears.
Select System Setup.
Select Map Datum.
Select datum you want to use from List.

Keep in mind that WGS84 is the same as GDA94 (well so close it dont matter) - the MLR SP24 probably doesnt have GDA94 so just use WGS84 in its place. The maps you have may use AGD84 or 66 - this should be on datum list in GPS.

Cheers
Greg
I sent one final shout after him to stick to the track, to which he replied “All right,” That was the last ever seen of Gibson - E Giles 23 April 1874

Lifetime Member
My Profile  My Blog  Send Message
Moderator

0
FollowupID: 498703

Follow Up By: Member - John L G - Thursday, May 03, 2007 at 15:08

Thursday, May 03, 2007 at 15:08
Hi Robin & Greg,

Well how easy was that.

Had a play just now and lo and behold the GPS now shows the new format so all I have to do now is go and have a play in the bush.

Many many thanks

John G
0
FollowupID: 498724

Reply By: Member - John L G - Thursday, May 03, 2007 at 14:01

Thursday, May 03, 2007 at 14:01
Robin & Greg

Thanks for the input and by far the clearest instruction I have had regarding set up of the GPS.

Now I have some homework to do, will have a play this pm and see where I end up. I can't advise the specifics of the charts as my son is bringinging them down to Collie on Saturday and we'll be going for a wander in the bush over the WE.

Am heading to the Gibson in a month for some serious stuff and have only recently started using the GPS in the bush. Before then I used to wander around the desert with 250 land maps using the topography for reference and in the sandy desert often counting sand dunes and ticking them off the map as we went. Deadly accurate, believe it or not, but didn't pay to lose count. Often reminded me of those maze puzzles in the old glossy mags such as Post or Pix, if you can remember back that far.

Thanks once again for the input.

Cheers
AnswerID: 237650

Reply By: equinox - Thursday, May 03, 2007 at 14:13

Thursday, May 03, 2007 at 14:13
Try this site John:

Here

Cheers

Looking for adventure.
In whatever comes our way.



Lifetime Member
My Profile  My Blog  My Position  Send Message

AnswerID: 237653

Sponsored Links