evilC Posted December 20, 2002 Share Posted December 20, 2002 For those of you using the yellow etrex, and still using firmware 2.10 or earlier, you may want to make a mental note that when you select the NZMG display format ("New Zealand") the unit automatically updates the datum to GDA instead of Geodetic Datum '49. I only "discovered" this automatic datum change when trying to trying to convert between NZMG coordinates and WGS-84 recently. I didn't see the datum change, and then read out lat and long using GDA (Australian datum) instead of WGS-84 which is what I had selected previously. Anyway, did some research, and eventually decided to upgrade my etrex firmware to 2.14 which is the latest version on Garmin's site even though there was no mention of any changes in this respect. However it is different, and version 2.14 changes the datum to Geodetic Datum '49 instead of GDA when NZMG is selected as the display option. Obviously that was what it was meant to do all along, although I'd rather it didn't change the datum automatically at all. Possibly other similar units have the same problem if using older firmware? Cheers Clive Quote Link to comment
bread Posted June 17, 2003 Share Posted June 17, 2003 Hi Clive Im new to this game and have purchased a Magellan Sportrak. Nice GPS but having fun trying to get some accuracy on waypoints in NZ Map Grid. The data for the 'user grid' puts me 200m to 300m out of position. Just thought you may be able to shed some light on the subject. Also I know the Garmins have the NZMG built into their software. how accurate and your waypoints usiing the NZMG coordinates? Cheers Brian Quote Link to comment
+kaimaikid Posted June 18, 2003 Share Posted June 18, 2003 Not too sure if you know but all the cache co-ordinates are in wgs84 or nzg2000 There are many paths to the top of the mountain....but the view is always the same.... Quote Link to comment
evilC Posted June 18, 2003 Author Share Posted June 18, 2003 G'day Brian (aka Bread) quote:Also I know the Garmins have the NZMG built into their software. how accurate and your waypoints usiing the NZMG coordinates? As you say, the Garmins (and hence my etrex) have the NZMG built in. The conversion between that and WGS84 or whatever is pretty much "spot on" as far as I know. So you can convert from WGS84 lat and long to NZMG for use with NZ topo maps if that is what you want to do. The NZMG is a very "specialised" grid though, and as far as I know it isn't possible to get a very accurate approximation using the "user grid" type approach - at least not across the whole country. Not that I have ever really had any need to attempt this myself... Cheers Clive Quote Link to comment
bread Posted June 18, 2003 Share Posted June 18, 2003 Hi Kiamaikid Love your phillosophy but unfortunatly it doesnt give me the answers to the universe I was looking for. Anyway, Yes I belive the cache coodinates are in lat/long. I havent participated at the sport yet, still trying to get my GPS to do what I want it to. I intend using my GPS for tramping and general swanning around the country in conjunction with the NZ topo maps. The waypoints need to be in NZMG coordinated to match my map but having difficulty setting it up. Before I send the Magellan Sprotrak back and buy a Garmin I was trying to find out how much accuracy the Garmins give using the NZMG and topo maps? Do you know of any others who have a Magellan that can help me in my endevours? Cheers Bread Quote Link to comment
+kaimaikid Posted June 18, 2003 Share Posted June 18, 2003 Sorry dude.....what part of NZ are you in? I currently own a magellan gps 320 and have found it to out perform the garmin 12, but mine has issues reading the true battery level..... Sorry, I haven't bothered with NZMG, but there is a crowd in Auckland who import them, the dealer who sold it to you should be able to put you onto them..... There are many paths to the top of the mountain....but the view is always the same.... Quote Link to comment
evilC Posted June 19, 2003 Author Share Posted June 19, 2003 If you want more info about the NZMG and how to convert to and from GD49 look on the LINZ site: http://www.linz.govt.nz/rcs/linz/6137/nzmg.pdf Here are links to a site showing how to use user grid to approximate NZMG and also shows errors you can expect. http://www.ualberta.ca/~norris/gps/nz/NZ.html http://www.ualberta.ca/~norris/gps/nz/NZ4.html There are also various tools and online sites that can convert between NZMG and lat and long with various datums. Good luck! Quote Link to comment
bread Posted June 19, 2003 Share Posted June 19, 2003 Hi to you all I think I've got it licked!! i have changed the faise Northings and Easting to include the error I was getting and it seems to have worked. I have tested it on a number of survey points obtained from the LINZ website. These points have very accurate Lat/Lon and NZMG coordinates. Fed the NZMG coordinates into my GPS and got very close lat/lon projections. I will now load in some known sites around Auckland /Papakura area and see if I can find them. Thanks for all your help. See you all on the playing field Cheers Brian Quote Link to comment
Hairy Little Dwarf Posted June 26, 2003 Share Posted June 26, 2003 Hiya Bread, A bit late, but we Dwarves operate on a different time scale to you humans Both my Garmins readily switch coord datums. that is, enter a WGS84 lat/long, then change the datum to NZMG, Icelandic or Siberian Mushroom Grid (whatever) and the coords are converted to the new numbers. There you go. Hope the procedure works with the Magellan. HLD I aim to become immortal. So far, so good.... Quote Link to comment
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