Navigation Question

[Rigson]

When you have latitude/longitude coordinates, (down to the second) how close will that bring you to the target? Example-within 100 meters, 10 meters, etc.

Cheers!

 

[Dave568]

One degree of latitude or longitude is equal to 60 miles. Each degree is broken up into 60 minutes, each of which represents one of the sixty miles. Each minute is broken up into 60 seconds, each of which is 1/60 of a mile. Since a mile is 5280 feet, you can then multiply 5280 by 1/60 to figure out how many feet are in one second. The answer comes out to 88.

So, you can expect a pair of coordinates that are accurate to a whole second to be within 88 feet of the target. However, you can also have decimals in the seconds of a coordinate pair, so you can get even more accurate. With a second that contains three decimal places, for example, you can pinpoint an object to within an inch or even less.

 

[Blue Sky]

When you have latitude/longitude coordinates, (down to the second) how close will that bring you to the target? Example-within 100 meters, 10 meters, etc.

Cheers!

There is no single answer. The distance between units of longitude depends on your latitude because the lines of longitude get closer together as you move away from the equater towards the poles. The distance cut by 1 second of longitude is not the same at 89 degrees latitude as it is at the equator.

Dave568: one minute of arc (at the equator) equals one nautical mile, or 6,076 feet, not a statute mile of 5,280 feet.

 

[kr1]

There is no single answer. The distance between units of longitude depends on your latitude because the lines of longitude get closer together as you move away from the equater towards the poles. The distance cut by 1 second of longitude is not the same at 89 degrees latitude as it is at the equator.

Dave568: one minute of arc (at the equator) equals one nautical mile, or 6,076 feet, not a statue mile of 5,280 feet.

Blue sky is correct. That is why if someone is doing land navigation such as hiking, search and rescue, etc we usually use UTM coordinates, because a meter is a meter anywhere on the planet. And the UTM system is based on meters. The army uses UTM coordinates (ok not exactly but its pretty close to the same) but they like to call them MGRS.

Boats and planes use lat/long. People on the ground use UTM coordinates.

KR

 

[mr_wilson]

As a surveyor for an engineering company my rule of thumb is:

second = 30 meters or 100 feet
tenth of a second = 1 meter or 3 feet
hundredth of a second = 30cm or 1 foot

mike

 

[kr1]

second = 30 meters or 100 feet
mike

My rule of metric conversion for meters to feet. We all know that there are 3 feet in a yard. To convert to metric just treat meters as yards and add 10 percent. i.e.

Like Mr. Wilson says. 30 meters is going to be 30 * 3 = 90 and 10% is 9 added is 99 feet.

70 meters is 70 * 3 = 210 feet plus the 10 percent is 231 feet.

If you are an old timer like me meters was a real challange. I learned this little trick because everything in the army for ranging etc, was done in meters. I taught land navigation in the army so this helped for a kid who grew up non metric. When I got out of the army and was teaching orienteering we again used metric maps and this helped me a lot, once I figured it out.

FWIW,
KR

 

[Rigson]

Thanks for the responses!:thumbup:

Blue sky is correct. That is why if someone is doing land navigation such as hiking, search and rescue, etc we usually use UTM coordinates, because a meter is a meter anywhere on the planet. And the UTM system is based on meters. The army uses UTM coordinates (ok not exactly but its pretty close to the same) but they like to call them MGRS.

Boats and planes use lat/long. People on the ground use UTM coordinates.

KR

KR,
What does UTM stand for?

 

[xbxb]

Here is UTM
http://erg.usgs.gov/isb/pubs/factsheets/fs07701.html

 

[xbxb]

Mgrs can be found in widipedia

 

[Watchful]

When you get the hang of it, UTM is a lot easier. Many construction-related civil projects are now using UTM due to its inherent coordination with GPS and GIS systems. It's good to know both systems (lat/long and UTM), of course.

 

[mr_wilson]

Universal Tranverse Mercator is just one of the established projections/systems in use in the world today. Most commercial airplane and boating GPS units operate in latitudes & logitudes for their positional information and the actual number of differing systems/projections around the world today is downright staggering to the layperson. Military GPS equipment as noted above for the most part come hardwired to operate the way the military requires, in UTM.

FWIW, the Trimble GPS data collectors in use today by surveyors operate primarily in the newer WGS84 projection and project location and set-up will normally determine into what projection data is downloaded and processed into. As a pipeline company we tend most often to operate in NAD 83 datum of either utm or lambert depending on the state our work is in.

Down here in Texas we still operate in "lambert" projection systems but as noted UTM is the one most commonly used in the military.

WGS84, NAD27, NAD83, HARN(HPGN), UTM and it's corresponding "zone" in conjunction with the distance units (meters or US survey feet just to name the 2 most common, there are more) you prefer the data to be in are just a few of the systems/projections used in North America today.

One of my primary responsibilities is the downloading and processing of Trimble GPS data files from our survey crews all over the planet and trust me ya don't even want to go any deeper down this rabbit hole, as it's a complicated issue, (especially for an old chain & transit guy like myself) all of which simply put relates to "where" one is on this planet.

mike