I'm wanting to be able to take two coordinate points, and using a little pythagoreum magic, come up with the number of feet between these points.
I'm doing that because I want to double check these POI files and see what points might possibly be duplicates of the same intersection.
I'm starting with
((lat-lat)^2 + (long-long)^2)^.5
then multiplying the result by 3600.
That 3600 multiplier is not going to give me what I want, I now see, as I'm probably just going to end up with the number of degrees between those two point, but not on a normal grid orientation.
Do I just take the circumference of the earth (roughly 25000 miles) and divide by 360 to get the number of feet in a degree?
You may want to a web search.. There appears to be a BUNCH of info on the web on this subject..
PS An alternative to the pythagorem theorem approach might be to combine all of your csv files into one spreadsheet. Next convert long and lat to an integer number so that the 4th decimal place shows as the last digit (e.g. convert long 90.0001 to 900001) Then do a 2 level by long/lat on the converted integer numbers. After this you could then compare subsequent entries to see if they are the same (or maybe close to the same). Those that pass the test would be the duplciates..i.e. within about 36ish or so??? feet of one another. (note that my decimal place and feet guess??? in the above might not be the most accurate guesses and/or what you'd want to use..)
I'm sure there are other approaches but this one just jumped to the top of my mind..
I found this on Hypernews.org. It was posted by The Sentinal.
A degree of latitude is 60 nautical miles, or 69.04 statute miles. A minute of latitude is equal to one nautical mile, or 6076 feet; thus, a second of latitude (6076 divided by 60) is 101 feet, 3 inches. Conceptually and practically, latitude is the same no matter where you go on earth; however, in reality it varies from 69.41 statute miles per minute at the poles to 68.70 statute miles per minute at the equator due to the earth bulging slightly from its rotational spin.
Longitude, of course, varies in length according to degree of latitude. The following is a sampling of longitude lengths for selected latitudes, beginning in the southern US and working north.
30 degrees North, (approximately Houston, Texas) a degree of longitude is 59.96 statute miles, 5274 feet per minute (almost equal to a statute mile), 88 feet per second.
35 degrees North, (approximately Albuquerque, New Mexico) a degree of longitude is 56.73 statute miles, 4992 feet per minute, 83.2 feet per second.
40 degrees North, (Kansas/Nebraska border), a degree of longitude is 53.06 statute miles, 4669 feet per minute, 77.8 feet per second.
45 degrees North, (Montana/Wyoming border), a degree of longitude is 49.00 statute miles, 4312 feet per minute, 71.87 feet per second.
49 degrees North (US/Canada national boundary), a degree of longitude is 45.40 statute miles, 3995 feet per minute, 66.59 feet per second.
50 degrees North (approximately Powell River, BC, Medicine Hat, Alberta, and Winnipeg, Manitoba), a minute of longitude is 44.55 statue miles, 3920 feet (1195 meters) per minute, 65.34 feet (19.9 meters) per second.
55 degrees North (approximately Ketchikan, Alaska and Dawson Creek, BC) a degree of longitude is 39.77 statute miles, 3500 feet (1066.8 meters) per minute, 58.33 (17.78 meters) per second.
Finally, 60 degrees North (southern border of the Northwest Territories), a degree of longitude is 34.67 statute miles, 3051 feet (930 meters) per minute, 50.85 feet (15.5 meters) per second.
This website has a explanation along with an 'online calculator'. This may help.
Using Google Pedometer, I ran a little test in my neighborhood and came up with 497 ft between two street corners. Pulling their coordinates from Google Maps, I put them in your formula with the 25K mile circumference and divided by 360 as you suggest. Your formula came up with 518 ft. I think that is amazingly close. I'm sure the other methods are still more accurate, but you asked whether your method would work and it sure looks as if it does.
Here's an online calculator.
It's not simple math because the distance between degrees of longitude changes with your latitude.
As stated by Spullis above, 60 miles (5280 feet) per degree is a reasonable
"estimate" for calculating distance in North America.
We used that figure in calculating rough distances travelled by Hurricanes in the Hurricane Chat Rooms. Certainly not exact but fairly close.
RT's calculator gives a result of 506 ft instead of the rough 518 given by zydeholic's formula.
Longitude At the Equator (0° latitude):
1° of Longitude is 111.3195 Km (69.17073 miles)
Longitude At the Poles (90° latitude):
At the Poles - all lines of Longitude converge to a point - there is no distance between them.
Longitude At Other Latitudes:
At other Latitudes, the distance between longitudes decreases the further North (or South) you go.
The Formula for Longitude Distance at a Given Latitude (theta) in Km:
1° of Longitude = 111.41288 * cos(theta) - 0.09350 * cos(3 * theta) + 0.00012 * cos(5 * theta)
One degree of Latitude is roughly the same everywhere.
Latitude At the Equator (0°):
1° of Latitude is 110.5743 Km (68.70768 miles)
Latitude At the Poles (90°):
1° of Latitude is 111.6939 Km (69.40337 miles)
I finally found the thread where this topic was discussed previously. Check:
Got'ta give viger6 credit for originally posting the online calculator at:
Another site to obtain distance between sets of coordinates is:
Here is a link to a website which contains an Excel Addin which is free for downloading and use.
function with gives you the distance between two points on a sphere
given two points returns the initial bearing of the great circle route
given a position, bearing and distance, returns the new position following a great circle route
converts degrees, mintues, seconds to ddd.mmmss
converts decimal degrees to ddd.mmmss
can compute the closest distance between a point and a line segment
many other trig functions
Can always count on Motorcycle Mama to have to correct answer without trying to over-impress.
Of course, given a sextant and a good 2 time zone watch... should be able to figure out where you are at any given moment.
Don't flame me... just teasing.
And I'd love to learn celestial navigation.
Motorcycle Mama rocks with her facts. Tell us MM, what do you do for a living that makes you so knowledgeable? Does it come from a) being a teacher, b) being a scientific type, c) being a mama to tykes, or d) being a biker who gets around and discovers all these great facts to share with the rest of us.
Thanks, GC0110. That's very kind of you to say.
a) No, although people sometimes tell me I should teach.
b) Yes. Very much so.
d) YES!!!!!!!! Absolutely!
Actually, what I do for a living has nothing really to do with electronics or scientific stuff.
I often refer to myself as an "information junkie". I'm always reading or researching something. I have a logical mind and like to figure things out and figure out how things work. I've often said that I learn a lot by answering people's questions and that is very true.
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