Stupid question on GPS marks

[Adamy]

Hi all,

I'm a GPS newbie... just got a magellan meridian. trying to manually load some of the GPS marks I have from off the web and noticed that some have 3 digits in the Last part of the latitude line and some have 2 - why is this and how do I get my unit to register that there are only two digits?? eg: 27.08.60S (2 digits) and 27.10879S (3 digits).
Can anyone enlighten me?

Thanks,

Adam

[finga64]

I'd just bung another zero on the end of the 2 digit number, never really had that problem thinking back. [smiley=uhoh.gif]
But I may be wrong and stand open for correction if I'm wrong.

[frankj]

Hello Adam

There will be a menu setting for co-ordinates in you GPS. Your GPS appears to be currently set up for degrees, which matches to the 27.10879S (= 27.10879 degrees South)
If you change the co-ordinate setting in the menu to deg/min/sec then you can enter 27.08.60S (= 27 degrees 08 minutes 60 seconds South.) You can switch this about as you see fit and it will change the display of any co-ords already entered in. In this way you can enter co-ordinates in whichever form you receive them.

Cheers
Frank

[finga64]

Oops, didn't see/take notice the decimal points ::)
I'm a dope [smiley=dunce.gif]
Thanks frankj :)

[Adamy]

Ah huh excellent feedback..... dont know how to apply it yet... gotta learn to use this thing better. But thanks soo much!!
Adam

[Cruiser]

Just be careful what units you're marks are originally written in. Decimal Degrees as opposed to Degrees, Minutes, Seconds have been mentioned above but most marks in marine and aviation are given in Degrees and decimal Minutes.

One give-away is any number greater than 59 in what appears to be minutes or seconds area.

The example 27.08.60S above will not be Degrees, Minutes, Seconds because the 60 seconds can't exist (it would be 27deg, 9minutes, 0 seconds in that case). I suggest it is more likely 27 degrees, 8.6 minutes and would normally be written as 27 08.600 S.

Chris.

[frankj]

Well Chris I would agree 27 08.600 S is 27 deg 8.6 mins, but I took the 27.08.60S to be a ficticious example made up by Adam.
I was under the impression a co-ord written as say 27.08.59S would represent dd.mm.ss
whereas 27 08.59 S would be as you say deg min

But I could be wrong.

Cheers
Frank

[Adamy]

Hmm controversy... I like it haha at least if we see som differing opinions we might get to the heart of the matter. Ok heres a real and actual example.... The following marks come from http://www.nuggetfishing.com.au/GPS.shtml : - Huybers Light Well known beacon 27.26.961 S 153.14.656 E
I can record this mark as there are 3 digits for both the last lot of numbers after the last decimal point however in the following set for the known wrecks: ABILITY 33,03,00 152,27,00 I dont know how to enter these figures due to commas and also 2 digits after the final comma.

Another example from this site: Brennan's Reef species. Reef bottom. 27.01.23 153.29.13 again two digits after the final decimal point - my gps wont let me record these marks without placing a 0 after the two digits

Does that clarify the question??

[frankj]

OK,

27.26.961 S 153.14.656 E would equate to 27 degrees 26.961 minutes south, 153 degrees 14.656 minutes east. GPS co-ordinate set to deg/mins.

33,03,00 152,27,00 would equate to 33 deg 03mins 0 secs South, 152 deg 27mins 0 secs E ; GPS co-ords set to deg/min/sec

27.01.23 153.29.13 would equate to 27 deg 01mins 23 secs South, 153 deg 29mins 13 secs E ; GPS co-ords set to deg/min/sec

Alternatively instead of changing the co-ordinate system on your GPS you could do a conversion using a site like this
http://www.cosports.com/tools/gps_coords.htm

Cheers
Frank

[Adamy]

Ah ha!! makes sense now... and an answer I can use in the monster unit... now al I have to do is find out how to get to the marks I've input. Thanks!!!

[frankj]

Lets hope you catch some fish.

Frank

[uripper]

Frank J

Do you have laymans explanation of the old 66 datum & current 84 datum ??

What is approx difference ??

Can an old 66 mark be easily converted to 84 datum ??

thanks in advance - Mal M

[frankj]

My understanding is the difference between AGD66 and WGS84 can be significant (in excess of 200 mts in a roughly NNE direction) it varies around Australia so a simple conversion may not be accurate.

My GPS will allow me to set AGD66 as the datum, so I could input an AGD66 mark and then change the datum back to WGS 84 and the GPS will handle the conversion. But, I haven’t done this in practice. Caution is required because the GPS will apply a consistent conversion, whereas, as I said the difference varies depending on where you are around the coastline. I think for the Brisbane area the difference is about 206 mts, whereas Perth is about 194 mts and Tassie 201 mts.

One way to check is to take a known point on your AGD66 chart, change your GPS to AGD66 enter the co-ords change back to WGS 84 and check the WGS 84 result against a WGS 84 chart, or simply go to the position. Any significant error will be apparent.

Just a little disclaimer here, this is to the best of my understanding don’t take it as gospel.

Frank