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Forum Index : Other Stuff : GPS co-ordinates confusion.....HELP!
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
I never had to deal with GPS co-ordinates before. Normally, you just type in the address of where you need to go, and away you go - simple. 
However, I have a project coming up where all the destinations are in the middle of no-where, and there is NO street address. What I DO have, is all the co-ordinates for the sites I need to go to, but I can't find any simple way to interpret them. I would love to be able to enter these into Google Maps, and have it show me where the site is, but the likes of Google Maps wants the co-ordinates in a format that I have not been supplied the GPS data in, and I am totally lost trying to convert into the decimal format that Maps seems to want. An example GPS data I have from the list of sites I need to go to is: 45 degrees, 52.1 mins S - 170 degrees, 30 mins E Whenever I try to put that into Maps, it puts me out in the middle of the Pacific ocean, thousands of miles from the nearest land, and I know for a fact that there ain't no site out there!!!! Can anyone help me? I ask this here, cos there are lots of clever people on this forum, and searching the net tonight has only resulted in hundreds of hits on how you go about obtaining your CURRENT POSITION in GPS co-ordinates from your GPS or Google Maps, and I need to go back the other way - I have the co-ordinates, I need to be able to put them into Maps or my GPS, and have it show me where that is in relation to where I am now - IE: How far away from here, are the co-ordinates I entered. It does not help that I don't really understand what the co-ordinates format is that I am using. The top of the chart says: "Approx GPS: DD-MM.mmm" Appreciate any help or links people might have were I can plug in the figures I have here, and have Maps show me where that location is. Any conversion utilities that will convert what I have into the decimal format Maps wants would also be immensely useful. Smoke makes things work. When the smoke gets out, it stops! |
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| greybeard Senior Member  Joined: 04/01/2010 Location: AustraliaPosts: 161 |
170 degrees 30 minutes east probably is in the pacific ocean given that it's nearly dead opposite the prime meridian running through Greenwich in the UK. And 45 deg 42.1 south is about halfway between the equator and the south pole. So without looking at a map,i'd say that it probably is in the middle of the south pacific ocean. Sure you've got the coordinates correct? DD-MM.mmm is degrees-minutes.decimal minutes [edit] ok, had a bit of a look, somewhere on the south island of new zealand (near enough to somewhere in the south pacific 
http://www.satsig.net/maps/lat-long-finder.htm [edit-edit] queens drive in Dunedin NZ |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
Yes, these are correct co-ordinates from the sheet given to me. Those example co-ordinates should put you at York Place in Dunedin. Queens Drive is about half a km away from where those co-ordinates should put you. I am playing with a known location on the list first, so that what I get back has to match what I know to be true - then I should be on the right track for the other ones on the list. How did you find Queens Drive using that example? If I look at your link, I cannot find anything obvious where I could plug in my figures and see where it takes me.  Smoke makes things work. When the smoke gets out, it stops! |
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| greybeard Senior Member Joined: 04/01/2010 Location: AustraliaPosts: 161 |
Scroll down under the map to where it says "or centre the map around lat" Have a read of the instructions regarding north /south east/west and polarity of coordinates. And in then convert the minutes to a decimal. ie 45 deg 52.1 south = 45 + 52.1/60 = -45.8693 - because it's south. and for 170 deg 30 min east -> 170.5 (+ for east) |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
Thank you for the example - I will have a play around and see what I can come up with. EDIT: Yes, I have it worked out now. Many thanks.
So, because Australia and New Zealand is south of the equator, the latitude is always a negative number and the longitude is always a positive number when converted to decimal. Latitude, Longitude = ((Minutes South / 60) + Degrees South), ((Minutes East / 60) + Degrees East) Using that formula, I have plugged in a couple of sites I have already been to, and Google Maps puts the marker in pretty much the exact spot - give or take a little, as I think these co-ordinates are quite old, and when taken, devices that could do that would not have been as accurate as they are today. Thanks a bunch. 
I will do more practise so as to get used to doing these calculations for later. Smoke makes things work. When the smoke gets out, it stops! |
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| greybeard Senior Member Joined: 04/01/2010 Location: AustraliaPosts: 161 |
NZ isn't that big just look out the window or ask anyone, they're probably related to who ever lives there.  |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
LOL!!!!  
Not far from the truth, really. And something I HAVE done before with great success - "Hey, mate! Where the hell is Joe Blogg's farm?" Some farm-boys can be very helpful with directions, and I have even had a couple who escorted to to the really hard to find sites. I appreciate your help, cos if you or someone else had not posted, I still don't think I would have worked it out. Once I had your example formula, it was easy. Not having ever had to deal with co-ordinates before, I was just a little out of my depth. I would not make a good ships' captain. I would not be able to navigate home! Smoke makes things work. When the smoke gets out, it stops! |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 6098 |
Here is a little program I prepared earlier 2016-09-17_225856_Coordinator.zip Simply paste the supplied coordinate into the top text box and choose the preferred format from the other boxes. 
Jim VK7JH MMedit MMBasic Help |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6098 |
And then you have to deal with different datum. In Australia, most current printed maps use the Australian Geodetic 1966 datum. This gives an error of about 200 metres when compared to the GPS datum. Until recently, when I gave the authorities the location of a radio transmitter, I was required to use the old 1966 datum. Now, they will accept WGS84 as well. My 1984 NZ maps don't declare their datum but a digital map set I have uses a datum of NZGD2000 I think that NZGD2000 is close enough to WGS84 but if you are getting data from old maps, it could be in NZGD1949 I am not sure what the differences to the GPS are but fortunately, the mapping program I use can handle lots of different datum (106) from around the world. What it all means is, you can not be sure what datum the data is given in so a test for each source is recommended before you start digging for buried treasure in the wrong back yard. Jim VK7JH MMedit MMBasic Help |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
The co-ordinate sheet also has a "NZMS 260 Grid" and "Approx. ASL" columns, but I did not know what they were. Does that mean anything to you? Awesome little converter utility - thanks - have downloaded it. Smoke makes things work. When the smoke gets out, it stops! |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6098 |
You need to look at this http://www.linz.govt.nz/data/geodetic-system/download-geodetic-software/nz-map-reference-converter-download The co-ordinates you gave are not in NZMS 260 Grid but the converter program in the link seems to cover both NZGD1949 and NZGD2000. You still need to work out which datum your co-ords are in - NZGD1949 or NZGD2000. Jim VK7JH MMedit MMBasic Help |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Way after the fact I suppose, but I just put 45.868333S 170.5E straight into Google & it gave me a rough location. Then I switched to Maps from the Google result & found myself in North Dunedin. Phil |
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