general gps cord's

[rediguana]

Yeah, but the co-ordinate system and projections are entirely different and you can mix them up however you want. Not that its right but it adds to the confusion sometimes. For example, I can easily write

dd mm ss (WGS-84) and
dd mm.mmm (GD49 - although this is usually shown in NZMG which completely avoids the confusion with lat/long & WGS-84)

The GPS won't stop you from setting the above combinations. And I can assure you they're made for some fun cache hunts in the early days

The best way is probably to assume co-ordinates on this site (for example) are all WGS-84 unless otherwise specified. I would also suggest where possible using NZMG for displaying GD49 co-ordinates.

I certainly haven't seen any standards, and would be interested to be pointed at any should they exist.

Cheers Gav

[evilC]

People reading this thread might also want to read this earlier discussion about datums, and then this is this one touching on some similar issues.

Probably others also - I only searched for posts that *I* had made!

I'd also be interested in hearing if any other (perhaps Garmin only?) GPS receivers have the same "feature" as my old style yellow etrex of automatically switching to Geodetic Datum 1949 (GD49) whenever you select the NZMG as your display format, but then not doing anything to the datum selection when you later change the display format back to one of the latitude/longitude options?

I guess it's a fair enough thing to do but it would be better (IMHO) if the unit warned you when the datum was being changed automatically (and preferably also reminded you that you might want to review the datum setting when you chose to switch away from GD49 datum later). This little trap has only "added to the fun" for me in times past when (more than once!) I went searching for a cache about 200m north of the real position, but it could possibly have more serious consequences one day.

[rediguana]

I think my 12XL did similar to the etrex, although I just tried it on my 76S and it gave you full flexibility over stuffing things up

[kiwilegend]

The 60CS automatically switches to GD49 if you select NZMG ( "New Zealand" ) and then back to WGS84 if you switch to lat/long

[evilC]

The 60CS automatically switches to GD49 if you select NZMG ( "New Zealand" ) and then back to WGS84 if you switch to lat/long

Does it always go back to WGS84, or is in fact going back to whatever datum you had set *before* switching to NZMG? I think that would be my choice if I was writing the software for these things...

And what does it do if, after switching to NZMG, you then change the datum from GD49 to something else? My choice for that case would probably be for the display format to revert back to whatever you were using before switching to NZMG.

[kiwilegend]

If anyone does do a FAQ - here is an example.
ALL THESE COORDINATES refer to ONE SINGLE SPOT. It's near the corner of Cable Street and Oriental Parade.
It just happens to be one reasonably obvious reference spot on a tracklog I had in Wellington:

WGS 84
S41.29248 E174.78524
S41 17.549 E174 47.114
S41 17 33 E174 47 07

Now to take my own advice, and punctuate it correctly:

S41.29248° E174.78524°
S41° 17.549' E174° 47.114'
S41° 17' 33" E174° 47' 07"

NZGD 1949
S41.29421° E174.78506°
S41° 17.652' E174° 47.104'
S41° 17' 39" E174° 47' 06"
or - if you want to be a bit more precise:
S41° 17' 39.1" E174° 47' 06.2"

NZMG
E2659502 N5988949

NZMS 260 sheet reference
R27 595889

NZTM
E1749478 N5427236

UTM
60 G 314555 5426408

Note: Both NZMG and NZMS 260 sheet references are GD49 BY DEFINITION. That's why they are less prone to confusion.
NZTM (and UTM ) are WGS84 (almost ) BY DEFINITION. We haven't seen much use of NZTM so far, but when the new LINZ maps come out, that's what they will have on them.
The colours in the NZMG and the sheet reference are the bits that are exactly the same in both.
In general, UTM shouldn't be used, as it is not optimised for our country. Use NZTM instead.

Hopefully I've got my NZMG/NZMS260 terminology correct. I never use it myself.
Please let me know if you spot any errors.

[kiwilegend]

The 60CS automatically switches to GD49 if you select NZMG ( "New Zealand" ) and then back to WGS84 if you switch to lat/long

Does it always go back to WGS84, or is in fact going back to whatever datum you had set *before* switching to NZMG? I think that would be my choice if I was writing the software for these things...

Good question. It goes back to WGS84. ( Simple, Stateless )

And what does it do if, after switching to NZMG, you then change the datum from GD49 to something else?

You can't. NZMG is GD'49 by definition. ( And you can't change it either )

[evilC]

And what does it do if, after switching to NZMG, you then change the datum from GD49 to something else?

You can't. NZMG is GD'49 by definition. ( And you can't change it either )

When I was younger, my father often said "there's no such word as can't". Strangely, my etrex agrees with him!

And all of a sudden I feel the urge to create a "puzzle cache" giving coordinates in "NZMG/WGS84" (I think I'll name this the "evil coordinate system", henceforth abbreviated to "EVILC". ). For once, those of us sticking loyally to the older technology will have the upper hand when it comes to finding it....

Sorry - we've gone off-topic...