Co-ordinates confusion

[wiley coyote]

I used an Etrex 12 gps, and an Etrex 30 gps to mark the same way point,but the co-ordinates were different. The Etrex 12 was S 36 45 886. E 143 48 852. The Etrex 30 was S 36 45 876. E 143 48 865. Why should they be so different? And, how many metres were they apart from each other? What is the most popular/ simplest, position format used by the forum members? I know zero about gps's , so any advice would be most appreciated. wiley.

 

[user 794]

Hi wiley c

I'm no expert but they seem to be very close and in a good gold area. Don't sweat too much on this area and the differences, unless you are getting to a great camping spot or a chute or something else specific.

I haven't measured but the difference seems to be metres.

i suspect the difference is in the Map Datum. Open both up and check that they are GDA94 or whatever.

Good luck

 

[Ded Driver]

for regular gps units, an accuracy within 10m is normal & acceptable.
There are higher resolution units, that with a subscription can give far better accuracy.
just one example https://positioningservices.trimble.com/services/rtx/

 

[AngerManagement]

Had a play = Not my cup of tea... Different standards and then getting the correct format ...

The Differences will come back to the Accuracy of the unit you are using and how many Satellites it is using - Higher end units will lock onto more Satellites and with better stability AND better number crunching - At best +/-5M usually +/-10M and while that seems large, it is not when you are travelling and you calculate speed. And most GPS Navigation systems have all sorts of fancy corrections to keep you on the road etc.

However for many reasons plotting a spot on the ground and returning to said spot is rather different and subject to reference datum points and or Defence needs. Surveyors etc have lots of tools to assist. For the average person +/- 10M when in the bush at sea or lost is close enough.

Do not know the cross roads at the point on Wimmera Highway = So it is your call. https://www.gps-coordinates.net/gps-coordinates-converter

3645'53.2"S 14348'51.1"E

= -36.764767 143.814200

Enter coordinates
-36 45.886 143 48.852 = Just plug that into Google Maps.

Decimal Degrees (WGS84)
Latitude Longitude
-36.764767 143.8142

Degrees, Minutes & Seconds
Latitude Longitude
S36 45 53 E143 48 51

GPS
Latitude Longitude
S 36 45.886 E 143 48.852

UTM
X Y
54S 751195 5927528

Then Part 2:

Enter coordinates
-36 45.876 143 48.865 = Just plug that into Google Maps.

Decimal Degrees (WGS84)
Latitude Longitude
-36.7646 143.814417

Degrees, Minutes & Seconds
Latitude Longitude
S36 45 52 E143 48 51

GPS
Latitude Longitude
S 36 45.876 E 143 48.865

UTM
X Y
54S 751214 5927546

 

[user 4386]

Etrex 12 was S 36 45 886. E 143 48 852. Etrex 30 was S 36 45 876. E 143 48 865

They are very close together (within metres) and simply reflect the accuracy of the instruments. If you try again tomorrow each instrument may give a very slightly different reading. Instruments often claim +/- 5 metres accuracy but in practice it can be as poor as +/- 15 m, although will APPEAR to be better on any one day.

It can also depend on what map datum you are using as someone said - check both are using the same datum.

 

[condor22]

near Bendigo 1000M is about 40 seconds of longitude

Therefore 1 second = approx 25 metres

Before getting into GPS accuracy you need to look at the quality of the GPS, age, accuracy. size of antenna etc etc.

No 2 GPS units will give identical readings. If you are within 10 M of the coordinates, be happy with that from a handheld. My E20 will state accuracy of 3 M at times, I don't accept that as Gospel.

If you want to be absolute, be prepared to spend in excess of $30,000 for a survey unit. They not only use satellite but are augmented by known fixed ground telemetry.

PS the figure of 40 seconds for 1km is at 33.5 degrees south, at the poles it's bugger all and at the equator much further, so the distance varies depending on Latitude.

 

[user 4386]

near Bendigo 1000M is about 40 seconds of longitude

Therefore 1 second = approx 25 metres

Before getting into GPS accuracy you need to look at the quality of the GPS, age, accuracy. size of antenna etc etc.

No 2 GPS units will give identical readings. If you are within 10 M of the coordinates, be happy with that from a handheld. My E20 will state accuracy of 3 M at times, I don't accept that as Gospel.

If you want to be absolute, be prepared to spend in excess of $30,000 for a survey unit. They not only use satellite but are augmented by known fixed ground telemetry.

PS the figure of 40 seconds for 1km is at 33.5 degrees south, at the poles it's bugger all and at the equator much further, so the distance varies depending on Latitude.

I have one accurate to 20 cm horizontally, one metre vertically - but it cost an arm and a leg (used for business so I can charge it out)