GPS Puzzle

[TrainChaser]

I don't know much about GPS.  Take that as a given.

I'm not going to the RTR, but I was watching Bob's video of  how to get there.  Near the end, he gives the GPS Location:  33*39'03.0 N, 114*08'45.4 W.

When I finally figured out the format to put in (33.39030 N, 114.08454 W), the pointer showed 18.37 (straight line) miles south of the actual RTR.

So I worked it backwards:  I found the location of the RTR on Google Maps, and then right-clicked and chose 'what's here?'  And the RTR location showed up as 33.65189 N, 114.148049 W.  HUH?

And, while the North America coordinates are usually shown with a minus in front of the second (W) number, sometimes it shows location in AZ, and sometimes in China.  I understand the WHY, but I don't know why sometimes it works fine w/ the minus, and sometimes it doesn't, doing the same thing.

Also, I asked Google what format to use to get a location, and one of them showed a degree symbol.  How would I do that?

Any info is welcome.

 

[abnorm]

For degree symbol.......°

On the number pad right hand side of keyboard........Num Lock........Hold Alt......0176


GPS problems ?.............I'm listening for the answers too............

 

[AngryVanMan]

Convert Degrees Minutes Seconds to/from Decimal Degrees

Geographic Coordinate Format Conversion - Wikipedia

Latitude and Longitude are most often expressed as Degrees ° - Minutes ' - Seconds " in standard or legacy mapping, expressing 60 minutes per degree and 60 seconds per minute, sort of like a clock. Decimal Degrees is a format that is easier to use when manually entering coordinates into general purpose computer systems, and the portion after the decimal point is the fraction of a whole degree in standard base 10, which is the number system we use and are familiar with for most day to day arithmetic applications.

As to your other question RE China/AZ - some mapping utilities will use N S E W to indicate the "side" of the meridian you are on, while others use positive or negative 180 degree notation. So 33°39'03.0 N, 114°08'45.4 W could be also represented as +33°39'03.0 , -114°08'45.4

Latitude
N or + : Northern Hemisphere, North of Equator
S or - : Southern Hemisphere, South of Equator

Longitude
E or + : Eastern Hemisphere, East of Prime Meridian
W or - : Western Hemisphere, West of Prime Meridian

If you use USGS terrain maps or were in the Military or Amateur Radio, you'd also be familiar with several other formats using grid systems, most notably MGRS, UTM, and MLS. If you've never called in a fire mission, contested during a field day, been orienteering, done land/sea nav, or hiked deep wilderness this is probably just alphabet soup.

 

[Optimistic Paranoid]

The gps app on my android phone gives both degrees-minutes-seconds AND decimal degrees.  I've read that if you call 911 from the boondocks, the operators want the decimal degree numbers, that's what they're trained to work with.

 

[FALCON]

I wish we could get everyone to switch to using only decimals format for coordinates. It's so much easier than degrees, minutes, and seconds.

That will probably happen right after we all switch to metric :-D

 

[TMG51]

Last RTR I followed the GPS coordinates given to the RTR site. When I arrived, there was only one person there. Ldmccain, who also followed the GPS coordinates. They were slightly wrong. Better to follow directions and look for signs.

But for GPS use I agree decimal format is preferable.

 

[TrainChaser]

Abnorm: Thanks for that!

AVM: I knew some of that stuff, but I thanks for explaining. Okay, you use EITHER the minus OR the N E W S. I think maybe I was using both.....

But I don't understand how I put Bob's coordinates in and the pointer on the map showed a place 18 miles south.

TGM51: "Better to follow directions and look for signs."

That would be nice, but the problem is that many people are incapable of giving directions. Why they can't go to Google Maps and look at the exit numbers, street names, and determine if a right or left turn should be made is a mystery to me.

 

[AngryVanMan]

The actual conversion of the DMS to Decimal for Bob's coordinates gives you 33.650833 N , 114.145833 W - if we take the "error" coordinates (33.39030 N, 114.08454 W) caused from the entering of the DMS into a decimal format directly by accident, we are off by -.2605 Degrees latitude (southern shift) and +0.061293 Degrees longitude (eastern shift). You can see that the southern shift is far larger than the eastern shift in this example, by about 2/10ths of a degree.

If you put them into a Latitude/Longitude Distance Calculator and chose Statute Miles (sm) as the unit (the normal land mile unit) you get a 18 mile distance between those two points on the sphere.

The error you introduce by directly entering the minutes as a decimal without converting properly first grows as the numerical minutes number gets larger, on the scale from 0 to 59. Here is a table for comparison:

Minutes (1/60ths of Deg)      Decimal Degree (Fraction)    Data Entry Error %

1                              0.0167                       0.67%
2                              0.0333                       1.33%
3                              0.0500                       2.00%
4                              0.0667                       2.67%
5                              0.0833                       3.33%
6                              0.1000                       4.00%
7                              0.1167                       4.67%
8                              0.1333                       5.33%
9                              0.1500                       6.00%
10                             0.1667                       6.67%
...
20                             0.3333                       13.33%
30                             0.5000                       20.00%
40                             0.6667                       26.67%
50                             0.8333                       33.33%
59                             0.9833                       39.33%

The third column in that table shows the percent of a whole degree that your position will be "off" if you accidentally enter the minutes directly into a decimal degree field on a GPS or computer. As you can see, the higher the numerical value in minutes, the larger the error will become, as a portion of a whole degree on the map. This is why your longitude (east-west) wasn't off very far, only about 5% of a degree, while the latitude minutes were 39' on Bob's post, introducing about a 26% error in the decimal degree fraction for north-south measurement... Each Degree on a map covers approximately 69 statute miles - so 26% error of 69 miles is very, very nearly 18 miles!

 

[ldmccain]

Last RTR I followed the GPS coordinates given to the RTR site. When I arrived, there was only one person there. Ldmccain, who also followed the GPS coordinates. They were slightly wrong. Better to follow directions and look for signs.

But for GPS use I agree decimal format is preferable.

[emoji4] was only a little off.
It is aggravating that each brand GPS and mapping program uses a different format for coordinates.
I've started using a GPS to just get me close unless I created the waypoint/favorite on that particular device or software...
Do need to order a Benchmark Atlas for AZ, not sure how I missed AZ when I was ordering...

Larry