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Uncle Rico

Geographic Coordinates

HE55’s recent post about Cascade Canyon got me to wondering about geographic coordinates and the different formats in which they can be presented. For instance, the coordinates for Cascade Canyon can be presented in either degrees/minutes/seconds format as 34°12'43.04"N, 117°39'39.42"W, or in decimal degrees format as 34.21196, -117.66095.  Both of those coordinate sets point to the same location on a map.

My potentially dumb questions are:

1. Why do these parallel systems exist and why do applications like Google Earth for instance use one instead of the other as its default?
2. Is there a benefit to using one format over another and is one more generally accepted/utilized than the other?
3. Is there an easy way to convert between the 2 formats that doesn’t require a computer program or an advanced degree in mathematics?
tracker

I've pondered that myself. If I had to guess, (since I don't really know, I am guessing), I would say the degree/decimal format is easier to understand and enter into equipment than the D/M/S.xx equivalent.
In the example you gave, the old school format would be capable of describing a 360,000th of a degree, whereas the new one would only go to a 100,000th of a degree.
If there are any Math Rambos in the audience, feel free to correct me. Smile
One of my old math teachers would say, "That's mighty thin baloney no matter how you slice it".
I've found the easiest way to convert one format to the other is to let my GPS do it. Go into setup/units/format and set the device to the format your numbers are being given in, if it isn't the same already. Then enter the numbers in question, as if you were making them a destination. Then go back into setup and change the device's format to the desired style. When you go back into operating mode, the coordinates you entered will be in the newly-set format.
I was doing this all day last Sunday on a wildlife guzzler survey. The old records were all D/M/S and the consensus was they needed to be in the new style.
tekewin

Wikipedia will show you how to manually do the conversion:
http://en.wikipedia.org/wiki/Geographic_coordinate_conversion

but I think you should always delegate that to a computer:
http://www.earthpoint.us/convert.aspx

There are many other coordinate systems: UPS, MGRS, USNG, Georef, Maidenhead, and State Plane. I think 0 longitude was agreed to be set in Greenwich, England as the international prime meridian.  It is a vast topic and I know very little.
turtle

Re: Geographic Coordinates

Uncle Rico wrote:

2. Is there a benefit to using one format over another and is one more generally accepted/utilized than the other?

It is much easier to calculate the difference (i.e. the angular distance) between two coordinates expressed in decimal degrees than between two coordinates expressed in degrees, arcminutes, arcseconds, and milliarcseconds. Proper handling of the 1/360, 1/60, 1/60, 1/1000 basis of the latter is extremely tedious.

Of course, even decimal degrees are based on a frustratingly arbitrary choice of 1/360 of the whole. Much better would be to use radians -- them's God's units.  Wink
RichardK

Coordinates

I don't like degrees in any format.  UTM is much easier.  The USGS 7.5' maps all have a UTM scale. Nat Geo Topo software and my Garmin GPS can work in UTM. I never use degrees of latitude and longitude.
Uncle Rico

Re: Geographic Coordinates

turtle wrote:
Of course, even decimal degrees are based on a frustratingly arbitrary choice of 1/360 of the whole. Much better would be to use radians -- them's God's units.  Wink




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