why I have a fat pocket pc and all this junk fixed to your car,
the better option is to buy a dedicated removable gps unit like the NAVMAN
N40i, which I highly recommend and leave a mobile to be just your mobile fone.
move it in and out of diff cars etc, take it with you to find your way around anywhere, man that feature helps spec when you go to a diff state or place.
trust me I know, man I went 2 qld and was able to better at navigating my wat round better then the local bogans LOL.
Plus with the NAVMAN you can take pix of places and store it in its memory,
best thing, find the pix in your gallery and NAVMAN takes you back there,
oh, and its not a massive unit like the TOMTOM. good value to 649 at JB's
all GPS work on an international datum that is WGS84, no matter where you are it will give you a location of where you are to about 5metres accuracy, Since you plan to buy one from HK the GPS would work of a datum in its area, normally all GPS would have all the datums available so all you do is choose the options in in that country area (in Aust its either AGM94 OR MGA66) thats why sometimes if you get a coordinate on the GPS and compare to the cordinate on your street directory its not exactly the same point, it would be off by like 5-20metres cos the GPS would be using a different datum compare to the street directory
well sometimes using a map is more convenient depending the situation ur at.
and dun juz rely on the gps
if ur fone runs out of batt then u will say y didnt i hv a map
all GPS work on an international datum that is WGS84, no matter where you are it will give you a location of where you are to about 5metres accuracy, Since you plan to buy one from HK the GPS would work of a datum in its area, normally all GPS would have all the datums available so all you do is choose the options in in that country area (in Aust its either AGM94 OR MGA66) thats why sometimes if you get a coordinate on the GPS and compare to the cordinate on your street directory its not exactly the same point, it would be off by like 5-20metres cos the GPS would be using a different datum compare to the street directory
all GPS work on an international datum that is WGS84, no matter where you are it will give you a location of where you are to about 5metres accuracy, Since you plan to buy one from HK the GPS would work of a datum in its area, normally all GPS would have all the datums available so all you do is choose the options in in that country area (in Aust its either AGM94 OR MGA66) thats why sometimes if you get a coordinate on the GPS and compare to the cordinate on your street directory its not exactly the same point, it would be off by like 5-20metres cos the GPS would be using a different datum compare to the street directory
actually the current Australian one is GDA94 which is the GPS converted AGD84 datum.
your right about generic gps unit being wgs84 though.... however without getting into too much detail about earth projections (flat objects wrapping around a sphere/globe) all country specific map datums will be slightly off (between 5m-100m) because of an international gps units setup. it is better to purchase an australian specific gps unit that will read an australian datum....
i know coz i do gis/demographics and play with map data all day and plotting client locations on GDA94 system when the coordinates or from a datum like NAD83 result in like a 200m discrepancy... this is especially bad the further away a location is fromt he centre of australia....
Pretty much think of it this way...
- The earth is a sphere
- Maps conveyed on mapping/nav/gps units are conveyed as flat objects..
- get a piece of paper and try wrap it around a ball... doesn't fit does it??
- Specific Projection systems are used per country to calculate the stretch of that piece of paper to be able to wrap around the ball properly from a central location.. hence GDA94 which is australia specific.
- Australia is a country in the lower part of the southern hemisphere... therefore the piece of rectangular paper has to be converted to an upside down trapezoid to display correct coordinates...
- WGS84 though universal on the other hand will not be as refined as it will calculate a location from earths core to surface (without getting into detail) to allow it to be used as a global datum.
Originally Posted by tron07
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and plotting client locations on GDA94 system when the coordinates or from a datum like NAD83 result in like a 200m discrepancy... this is especially bad the further away a location is fromt he centre of australia....
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