Who's wrong? ERSA or Google Maps?

[old man emu]

I've been using Google Maps to get the Lat & Long of useful 10 Nm reporting points from Tooraweenah. According to Google Maps, Tooraweenah Aerodrome is 31.44201S, 148.89801E. However, ERSA has the aerodrome at 31.2630S, 148.5400E. That's 20 Nm difference. I checked the ERSA numbers against a WAC chart, and they match. So, why is there a difference?

[Thruster88]

I think you are mixing decimal, with degrees minutes and seconds. Yes the calculator agrees. Google maps is a decimal representation.  

[Garfly]

I think the problem might be that the latter figures quoted could be minutes and seconds.

OzRwys has it at S31deg26mins24secs ;  E148deg54mins02secs

 

EDIT:  Yeah, it's a bit ambiguous the way ERSA writes those figures, that is:  "312630S   1485400E"

            in a document where ambiguity can be a big problem.  Mt Erebus comes to mind.

 

 

Edited December 31, 2022 by Garfly

[RFguy]

google maps you can select decimal degrees, or  deg min sec,  or deg decimal minutes....

 

OME says ": Tooraweenah Aerodrome is 31.44201S, 148.89801E ,  ERSA has the aerodrome at 31.2630S, 148.5400E"

ERSA is DMS (deg, min, sec)  .  Note that the ERSA DOES NOT have any comma or decimal point. (OME you indicated that it did  in your post) 
"312630S 1485400E"
When a fix of DMS is provided, there will be 6 numbers, groups of two digits. longitude here will be three digits for deg, and 2 for min, 2 for sec.
 

[facthunter]

I think it's crazy to use decimals. Your log books went the same  There's 360 degrees in a circle. That's divisible by a lot of numbers The earth is an oblate spheroid. 15 degrees as an hour of time. Arc to time gives you the real local time anywhere. Nev.

[old man emu]

2 hours ago, Thruster88 said:

I think you are mixing decimal, with degrees minutes and seconds. Yes the calculator agrees. Google maps is a decimal representation.  

Yep. I see where I cocked it up. I'll go back to the WAC and get the correct numbers.

 

Once again, thanks for the lesson.

[facthunter]

You are not the first and you won't be the last. It's set up to cause such errors.  Like spring back binders near Compasses.  Nev

[RFguy]

Where things become tricky and errorsom  is conversion of spheroids...

 

This usually occurs between sperical (lat long) and easting/northing etc cordinates, as , as nev says, the Earth is an oblate spheroid.

and also converting from good ol' AMG66 to WGS84 or even MGA84, or even LOCAL datums.

 

Large geo projects like the Snowy scheme have their own local datum, to better approximate the bulging earth in the region.

I got to learn all this when writing radio propagation prediction programs in the 90s, having to work with all matter of map data , fortunately I had a good mate Joe Monardo who was a surveyor.  We had spot height data in AMG66 or a local datum (councils had their own datums)  , and I fed this into a terrain forming program called ANUS-DEM from the ANU which was originally used for catchment predictions.

 

 

[old man emu]

Stupid Question # log e^x^n:

 

If I gave you the name of a location, e.g. Hickeys Falls NSW, and told you that the Google Map coords are -31.425607, 149.081188, and that the WAC coords are 312531, 1490452, which set of values would you use in your electronic flight planning gizmo thingy to fly there?

[old man emu]

4 hours ago, Garfly said:

OzRwys has it at S31deg26mins24secs ;  E148deg54mins02secs

the way ERSA writes those figures, "312630S   1485400E"       

 

 

ERSA is close enough for government work. One second of longitude is 80 feet.  1485402 is 160 feet from 1485400. If you can fly accurately to a second of longitude, you are pretty good. 😄

 

BY the way, I found this converter: https://tool-online.com/en/angle-converter.php

[Garfly]

1 hour ago, old man emu said:

ERSA is close enough for government work. One second of longitude is 80 feet.  1485402 is 160 feet from 1485400. If you can fly accurately to a second of longitude, you are pretty good. 😄

 

BY the way, I found this converter: https://tool-online.com/en/angle-converter.php

Oh, for sure, I take those coordinates [S31deg26mins24secs / E148deg54mins02secs  and 312630S  / 1485400E ] as the same thing for our intents and purposes (global bulges notwithstanding ;- ). I only meant to draw attention to the format ERSA uses and how ambiguous it could be for pilots, on quick viewing (as opposed, to geoscientists et al, who use all the various formats regularly).  I haven't kept my eye on just how ERSA denotes lat/long (we rarely need to match coordinates to maps by hand, these days) so, I could easily have made the same mistake you did.  So I reckon it should be disambiguated. 

 

Edited December 31, 2022 by Garfly

[Garfly]

5 hours ago, old man emu said:

Stupid Question # log e^x^n:

 

If I gave you the name of a location, e.g. Hickeys Falls NSW, and told you that the Google Map coords are -31.425607, 149.081188, and that the WAC coords are 312531, 1490452, which set of values would you use in your electronic flight planning gizmo thingy to fly there?

I prefer to use the DMS coords because that's how my OzRwys - and Google Earth - are (usually) set up. 

But anyway, for me, both apps (notwithstanding the different formats) placed the coordinates quite close together but at a distance of about 1.5 km to the east along the highway, from Hickeys Falls.  

I used GE first, to locate the place by name (it's not on any of the charts I have in OzRwys) and then matched up features to confirm and cross check.

I placed the falls themselves (just north of the associated carpark) at 312543, 1490401 

Or, in our sort of lingo, approx 9nm on the 074 radial FROM YTWN. 

Are those the kind of results you were expecting?  

 

 

CLICK FOR FULL REZ.

 

 

 

 

 

 

Edited December 31, 2022 by Garfly

[old man emu]

3 hours ago, Garfly said:

Are those the kind of results you were expecting? 

Not quite the answer I was looking for, but good info - thanks.

 

I was simply wondering what keystrokes one made to enter the information into your navigation gizmo thingy.

 

This is the diagram I am going to provide in the Pilot Guide.

 

[Garfly]

Okay, that looks good.  I can see that the precise location of the Falls themselves is not important in context. The road intersection is the waypoint.

 

I suppose you could also play with what3words fixes, which, I reckon, would put the actual falls at magician.opening.aboard  and the nearby intersection at uninspired.outsize.strategist and YTWN at assertions.springtime.investigated   ;- )

 

 

 

Edited December 31, 2022 by Garfly

[440032]

"Tooraweenah"?  OUCH! Don't hop the barbed wire then.

Happy New Year.

[Bosi72]

3 hours ago, old man emu said:

was simply wondering what keystrokes one made to enter the information into your navigation gizmo thingy

Which navigation gizmo thingy are you using?

[Old Koreelah]

 

Emergency services have long tried to standardise which Lat/Long system to use, so that we’re all singing from the same songsheet. In the end, we discovered it’s not a biggie, because rescue helicopters can also swap systems.

 

Degrees and decimals might seem attractive and simple, but DMS is easily converted to actual ground measurements: 

A Degree of latitude is 60NM, so a Minute is one NM and a second, as OME says, is about 30 metres.

 

One fact that always fascinates me is that the ancients divided the circle into 360 degrees; the French decreed the earth’s circumference to be 40,000km.

Divide 40,000 by 360 and you get 111.1111111 

This is useful when converting latitude marks on a map into kilometres.

 

[facthunter]

Works even better with NM. Latitude  spacing is fairly constant/even in reality but on a Mercator nothing is to scale except at the equator. The shortest distance between any two places is the great circle passing through each place having it's centre at the earth's centre. Only on a pole to pole  to pole path will that be a constant track. .   Nev

[old man emu]

1 hour ago, Bosi72 said:

Which navigation gizmo thingy are you using?

I don't have a digital gizmo. 

 

I have one  an E6B  one of these  and a 

[facthunter]

The question IS are the participants using GNSS/ GPS or is it kept in a sealed bag for when they get off the narrow path of virtue?  Do you have spotters checking the time and tracking accuracy. over hidden points?   It's not the fastest . It's the most accurate to the Plan.Yes?  Nev

[RFguy]

I use one of those with a bit of string knoted to the middle... VERY fast to use.

 

[Bosi72]

I would say majority is using whatever gizmos they have and keep the (most likely expired) paper charts in a sealed bag.

 

But the good news is to see people using gizmos to access these internet forums, upload photos etc, instead of, or in addition to, writing letters to flying magazines..

[old man emu]

2 hours ago, facthunter said:

The question IS are the participants using GNSS/ GPS or is it kept in a sealed bag for when they get off the narrow path of virtue?  Do you have spotters checking the time and tracking accuracy. over hidden points?   It's not the fastest . It's the most accurate to the Plan.Yes?  Nev

At the moment I am writing the Guide to Pilots for getting to Toora before the event. The questions I am asking at the moment are so that I can propose orderly approached to the aerodrome in an attempt to make it safe. Remember, it is an uncontrolled aerodrome, so I need to assure CASA that I've considered as much as reasonable to ensure that safety. If I have given pilots as much information as possible, and have asked them to fly along certain routes when coming to Toora before the event , then if someone wants to "do his own thing" and causes an incident, then that someone will have to explain why they diverted from the considered suggestions.  We will monitor the area frequency and anyone who does not make the appropriate calls will have 30 minutes added to their contest time. If the weather is forecast to be crappy, then the event will be postponed to a later date in hopes of good flying weather.

 

As for the contest itself, crews will submit a written plan before departure. As far as the contest is concerned, the only thing that matters is how close to the submitted ETA the crew's ATA is. In the spirit of the contest, i.e. navigation as it was in the 40s and early 50s, I hope that crews will test themselves by going by paper map, compass and timepiece. Strewth, the prize will only be a cheap tin mug. We aren't betting sheep stations here.

 

Just to keep the bastards honest, there will be a prize for the most professional flight plan submitted prior to the flight, and another prize for the most professionally completed plan submitted at the end of the flight. Don't forget that we are looking for candidates to interview for the position of DH86 pilot on Butler Air Transport feeder routes.

 

52 minutes ago, RFguy said:

I use one of those with a bit of string knoted to the middle... VERY fast to use.

 

Now that's a Handy Hint to the Housewife.

[old man emu]

NEXT QUESTION:

If  I have a Google Map and measure the bearing of Point B from Point A, is it Degrees True, or Degrees Magnetic?

 

If that bearing is from the 10 NM boundary, should I report the Heading from that point to Overhead Runway as X degrees (T), or X degrees (M).?

[Bosi72]

How do you measure bearings in Google Maps (unless you are referring to Google Earth which is in True degrees)?

 

Regardless, I would use paper chart and a protractor, get bearing in True degrees to/from whatever point you choose, then subtract 11 to get Magnetic degrees.