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Longitude & Latitude. Two ways to go?

G

gasman

Well Known Member
Friend
During ground school 38 years ago, we were educated on degrees and minutes. With this we could unfold any sectional and locate a spot and fly to it with out new found Loran radio.

Then came GPS. Punch in lat. and lon. and go to it. Several years later, the Homeland Security requested the location of our Propane storage facility in Lat/Lon. They wanted to post it on the internet for security reasons??? The uproar from the industry was able to stop that. But not till after we sent in the required forms.

Here is my point, I went to the yard and noted the lat/lon on my gps and gave them to my partner. He entered them in the web site, and later told me they were wrong!! That was not the right format..........:eek:

My thought then were....... gee this looks like it could become a problem. So, now it is a problem. How do we adjust for it so we are all on the same page?
 
Several potential issues here. One is whether the data were entered in degrees, minutes, seconds or decimal degrees. If you were using UTM coordinates, then the model that is used differs depending on your database (NAD27 is the North American Datum from 1927, used by most of the old topo maps; NAD83 is a newer version and in our area the difference is about 100 meters - that is, the same coordinates in one version are off by 100 meters in the other).

Link to Wikipedia site:
http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system

Cheers,
Greg
 
GPS uses WGS84, which is close to NAD83 but not identical. More expensive (professional surveying) GPS receivers allow selection of the datum from a list (there are scads of them, some global, some very local), with WGS84 being the default (although it initially computes position/velocity/time, or PVT, in X,Y, and Z in Earth-Centered-Earth-Fixed, or ECEF, coordinates).
 
Back about ten years ago, we were searching for debris from the Shuttle Columbia out in East Texas. Lots of teams deployed into the field with whatever GPS units they had, and started relaying coordinates to the field headquarters, where utter chaos over mapping and coordinate systems broke out. Different Datums (as described by Greg, above), different units....it was all pretty random, simply because well-meaning people would read numbers off the screen and read them in, not including the units or datum. It's all important.

If someone asks you "how long is that spar", and you simple answer "21", it does no good. You have to know the units with any measurement. It's not the equipment's fault - the user plays a part as well.
 
Back when I was teaching and the answer to the test problem was "5 ft/sec", students who put down "5" were marked wrong, no partial credit, just wrong. They hated it, but they also got the message: units are important.
Remember a few years ago when nasa lost a Mars mission because different groups were using different units?
 
Hmmm...

I wonder if this is the reason the location of the recent RV10 crash was mixed up by SAR?
 
use wgs84

This is the aviation standard. Hand held GPS units can be programed to use any of the standards, I guess so if you have an old map you could sync to it.
 
When specifying coordinates, you HAVE specify coordinate format and datum. For example:

UTM Zone 15N E123456 N3456789 NAD83 is unambiguous and (if I have done that right) specifies only one place on the surface of the earth.

38 13 45N 118 34 56W is ambiguous - DMS, or DM.S? Which datum?

UTM is probably the best coordinate system for SAR (we switched to it in the mid 90s in Oregon and were very happy). Township and Range is the worst. Sadly, T&R is still way too common.

TODR
 
The answer to the above question is, according to news sources, "yes". From the aviator's phone call to 911 operators to search and rescue there apparently was confusion over the units for lat and long.
 
Doug,

If I happened to be in the area and overheard "UTM 15N" that would mean nothing to me.
The various datums are not really that different, but the format is important.
I would suggest everyone should practice inserting the missing information:
e.g., "123 degrees, 52 minutes, 5 seconds north; .... (west)"; OR "123.456 degrees north, ....(west)". Add the datum if you know it, but either of these should get S and R close.
 
If you heard 15N, that would only tell you which map you were on and bearing in mind that each map is 8 deg wide, that is a big area.
You need to look at the paper map you are using and see what datum they use. WAC charts are using WGS 84. Look in the bottom left corner.
UTM UPS is useless for use with WAC charts as it is based on metres. The WAC is good because 1 minute of latitude is 1 n.m. and we use knots as our basic navigation speed measurement.
It seems that the USA uses knots or statute miles per hour at random, so the WAC is not easy for statute mile workings.
UTM UPS is great for ground work as you can work down to metre accuracy and comparing two locations is easy, just a simple matmematical problem, if you are on the same map. A bit tricky if you are comparing locations on different maps as happens where I live, close to the J and K divide of 24 deg South.
 
Totally confused??

I hope someone will take the time to explain this. Like many others I was not aware that there was more than one way to express Latitude and Longitude.
I am now looking at my settings in fore flight and there are 3 choices.
DD.dd degrees, or DD degrees MM.mm, or DD degrees MM' SS".
If I read my current location from the Lat/Lon read out to some emergency center would I have to get into my settings menu and also read
Capital Delta Capital Delta dot degrees lower case delta lower case delta as the format? :rolleyes:
I need help and I admit it.
 
N427EF said:
I hope someone will take the time to explain this. Like many others I was not aware that there was more than one way to express Latitude and Longitude.
I am now looking at my settings in fore flight and there are 3 choices.
DD.dd degrees, or DD degrees MM.mm, or DD degrees MM' SS".
If I read my current location from the Lat/Lon read out to some emergency center would I have to get into my settings menu and also read
Capital Delta Capital Delta dot degrees lower case delta lower case delta as the format? :rolleyes:
I need help and I admit it.
Click to expand...

Here's how I would do it:

Examples

34* 27' 18" N - "Three four degrees two seven minutes one eight seconds north"

34* 27.30' N - "Three four degrees two seven decimal three zero minutes north"

34.455* N - "Thirty-four decimal four fife fife degrees north"

Or say each one separately: "Three four decimal four fife fife..." Whatever works.

It's not that hard, it just has to be unambiguous. And whether it's NAD27, NAD83, or WGS84 datum probably doesn't matter THAT much in a search-and-rescue situation, and likely isn't worth messing around with your GPS settings under stress where you'll more than likely just screw it up. It's virtually certain to be using WGS84, so leave it alone and just call out the lat/lon on the display.
 
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More questions

Yes, thank you this is what I would have done before this thread appeared.

34* 27' 18" N - "Three four degrees two seven minutes one eight seconds north"

34* 27.30' N - "Three four degrees two seven decimal three zero minutes north"
Click to expand...

The reason this thread appeared is because of an apparent misunderstanding between a downed pilot and an emergency rescue crew. Apparently it caused a delay in finding the shivering crew and passengers by several hours. Knowing the format seems quite important all of a sudden.
Which part of all this is the "format" and where do I find it in my GPS gadget?
The same question for the datum line used. I really thought there was only one
datum line. where does it tell me what datum line is used.
38 13 45N 118 34 56W is ambiguous - DMS, or DM.S? Which datum?
Click to expand...

Really? they couldn't come up with a designation for a different datum line
other than adding a dot between the M and the S ??
Sorry, being a little sarcastic here but I really do want to know.
 
Ernst,

Datum is simply the model of the earth's surface. The earth is not quite a perfect sphere, so the various mathematical models try to account for that. As someone already noted, the datums are not different enough to affect SAR operation, they typically only vary by a couple hundred meters at most, and usually less than that.

In terms of reporting your position, think of it like reporting time (and in fact the position system is derived from time, thus the similar terms). You could report the time in hours, minutes, and seconds (09 hours, 29 minutes, 12 seconds)which is the older and most common method. Or you could report the time in hours, minutes, and fractions of a minute (09 hours, 29.2 minutes - the 0.2 minutes is equivalent to 12 seconds). Or you could report in decimal hours (09.4867 hours). Similarly, reporting position can be done in any of the three formats.

Of course, you could also report position in UTM (and your GPS can be set up to report this as well). The UTM coordinates will look and sound very different from degrees, minutes, seconds, and I doubt any SAR group would confuse these two types of position reports (UTM vs. D,M,S).

I would probably default to degrees, minutes, seconds rather than either of the other two. The main thing would be to be clear if giving a position over the radio. If it's an automatic GPS (like a personal locator beacon), the format will be obvious to whoever is looking at the data.

Hope this helps a little bit.

Greg
 
N427EF said:
Really? they couldn't come up with a designation for a different datum line other than adding a dot between the M and the S ??
Sorry, being a little sarcastic here but I really do want to know.
Click to expand...

Hmmmm....you may be being a little facetious here, but...

You wouldn't have DD MM.SS ... it would be DD MM.MM, and the format has nothing to do with the datum. You can show position in any of several formats with *any* datum chosen (except for UTM, which is shown as meters north and east of the origin for the specific zone, thus the terms "northing" and "easting" when talking UTM. But I digress :) ).
 
A little slow but getting there

Thanks for the help I have already learned a lot from this thread.
I had a feeling that others might not know either but wouldn't ask.

I grew up being told, that if you ask questions you are stupid but if you don't ask questions you'll stay stupid.:eek:
Those folks hadn't heard of self esteem.

Hmmmm....you may be being a little facetious here, but...
Click to expand...

Yes, a little facetious and sarcastic but otherwise good natured.
 
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