something for you oldies

I think this is the appropriate spot to point out that the mapped coordinates of a point on the earth depends on the spheroid and datum used for the mapping.

If the ones used for the map data are not the same as the one used by the GPS system, the position shown by GPS will be incorrect. Local mapping uses a spheroid and datum such that this mathematical surface corresponds to the equipotential surface as closely as possible for a mathematical model, e.g. Australia typically uses the Australia datum and Clarke 1858 spheroid. GPS, on the other hand, uses a spheroid and datum that tries to match the equipotential surface over the whole earth.

Unless there is a conversion between the two, usually in the GPS receiver or the map supplied to the GPS receiver, there will be a mismatch, which can run into hundreds of metres. And then there are straight mapping errors.

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Originally Posted by JDNSW

I think this is the appropriate spot to point out that the mapped coordinates of a point on the earth depends on the spheroid and datum used for the mapping.

If the ones used for the map data are not the same as the one used by the GPS system, the position shown by GPS will be incorrect. Local mapping uses a spheroid and datum such that this mathematical surface corresponds to the equipotential surface as closely as possible for a mathematical model, e.g. Australia typically uses the Australia datum and Clarke 1858 spheroid. GPS, on the other hand, uses a spheroid and datum that tries to match the equipotential surface over the whole earth.

Unless there is a conversion between the two, usually in the GPS receiver or the map supplied to the GPS receiver, there will be a mismatch, which can run into hundreds of metres. And then there are straight mapping errors.

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Hence, I'm having trouble pin pointing (For the sake of Qld surveying history) an old Australian Army Trig Station, outside Conondale, in Qld.

I have done a 'Scale Factor' adjustment, but the Co-ords I have for the Station are from the 1940s, so I'm going to rely more on contours, gut feeling and a bit of experience.

I'm just waiting for the weather to clear and a bit of a lower temperature, before heading into the scrub. I must be getting soft! [biggrin]

I'm surprised that with all this discussion regarding pin pointing locations that no one has mentioned 'What3Words' - the system that divides the world up into 3m squares and gives each a unique three-word address.
With W3W there are minor problems with homophones, similar sounding words and plurals but it is a lot more simple and less prone to mistakes than defining a location by latitude and longitude with degrees, minutes, seconds, N & S hemispheres plus E or W of the IDL.

Maybe we're all too old for it. :whistling:

never too old for some DR navigation......

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Originally Posted by ramblingboy42

never too old for some DR navigation......

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Used a bit of that on my first crossing of the Simpson - before GPS was available.
When we hit the French Line at right angles and soon after located one of the BM's placed along the French Line we discovered that we were about 1/2km out after a couple of hundred k's.

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Originally Posted by Xtreme

I'm surprised that with all this discussion regarding pin pointing locations that no one has mentioned 'What3Words' - the system that divides the world up into 3m squares and gives each a unique three-word address.
With W3W there are minor problems with homophones, similar sounding words and plurals but it is a lot more simple and less prone to mistakes than defining a location by latitude and longitude with degrees, minutes, seconds, N & S hemispheres plus E or W of the IDL.

Maybe we're all too old for it. :whistling:

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This does nothing to avoid the issue I described above, simply changes how you refer to a location. It does nothing to address the issues of what spheroid and datum are used, merely adds an additional computation layer.

And I am not too sure what the problem with degrees/minutes/seconds is - I am pretty sure I was understanding this by the time I had done basic spherical trigonometry about grade eight.

Quote:

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Originally Posted by JDNSW

This does nothing to avoid the issue I described above, simply changes how you refer to a location. It does nothing to address the issues of what spheroid and datum are used, merely adds an additional computation layer.

And I am not too sure what the problem with degrees/minutes/seconds is - I am pretty sure I was understanding this by the time I had done basic spherical trigonometry about grade eight.

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Agree with you there John but also think that, for the man in the street, the W3W system is a "lot more simple and less prone to mistakes".

Anyway, I'm still surprised that no one has mentioned it yet.

I have W3W on my phone. Haven't had a use for it as yet, but if needed is an alternative for location purposes I guess.

Quote:

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Originally Posted by Xtreme

I'm surprised that with all this discussion regarding pin pointing locations that no one has mentioned 'What3Words' - the system that divides the world up into 3m squares and gives each a unique three-word address.
With W3W there are minor problems with homophones, similar sounding words and plurals but it is a lot more simple and less prone to mistakes than defining a location by latitude and longitude with degrees, minutes, seconds, N & S hemispheres plus E or W of the IDL.

Maybe we're all too old for it. :whistling:

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I've just been and checked.
Neither of the 2 GPS on the boat have it, none of the GPS in the cars have it and my handheld GPS doesn't have it. The automated emergency reporting on the VHFs doesn't have it.

If I need help, I'm likely going to be in a situation where I don't have data, nor time to look up some form of translation from coordinates (which are pretty much universal) to words. It very much sounds like some mobile phone zombie had a thought bubble and saw an opportunity to solve a problem that doesn't really exist. 3 words : Whiskey Tango Foxtrot?

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Originally Posted by BradC

I've just been and checked.
Neither of the 2 GPS on the boat have it, none of the GPS in the cars have it and my handheld GPS doesn't have it. The automated emergency reporting on the VHFs doesn't have it.

If I need help, I'm likely going to be in a situation where I don't have data, nor time to look up some form of translation from coordinates (which are pretty much universal) to words. It very much sounds like some mobile phone zombie had a thought bubble and saw an opportunity to solve a problem that doesn't really exist. 3 words : Whiskey Tango Foxtrot?

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W3W doesn't need or use a GPS device. All you need is your phone and the what3words app.
Maybe the following will enlighten you regarding how W3W works
How to use what3words in an emergency?

• Find the 3 word address for your current location on the free what3words app for iOS and Android. ...
• Share your 3 word address over the phone to the call handler.
• The emergency service can then coordinate a response directly to the exact location where help is needed.