Getting a "square" of lat/lon for database query

Question

So I want to get the square formed by a single point of lat/lons, my plan was to take that point's latitude, divide by 360, and multiply by the circumference of earth. Giving us the distance from the equator.

Now I will take 1/4 the circumference of earth, and subtract by the distance from the equator, giving us the height of triangle T. I can the find the base because I know the initial height, truncated height, and the original base.

Now using the base and height I can use trig to find the minimum and maximum longitude, and the latitude is easy because lets are evenly spaced. Does this sound right?

EDIT:

Let me simplify this question.

How can I find the distance between two points of longitude, at a single point of latitude?

I think you need to work with Projected coordinate system and not geographic lat/lng since you cannot perfrom measurements with lat/lng. — artwork21, Apr 08 '13 at 01:03
Not sure what you are asking for exactly but maybe a look at Great-circle distance, the Haversine formula, and Vincenty's formulae will get you closer. — blah238, Apr 08 '13 at 01:25
Can you turn this into a comprehensive answer to the original question, paste it in below ("Your Answer") and click the tick (check) icon to make it "the answer"? Thanks — BradHards, Apr 08 '13 at 03:10

score 1 · Answer 1 · answered Apr 08 '13 at 03:15

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So for me the answer was, because I dont need that much accuracy, to use the Great-circle distance formula.

distance of one degree of longitude = Cos( longitude ) * radius * ( π / 180 ).

Distance of latitude = about 69 miles / degree

answered Apr 08 '13 at 03:15

OneChillDude

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This formula is correct for distance along a circle (it appears in many places on this site) but it is not the great-circle formula: a circle of latitude is a great circle only at the Equator. To see how incorrect it can be, consider the distance from, say, Mexico City (19.25, -99) and Bombay (19.25, +73) (which aren't too far from the Equator as it is). Your formula gives Cos(19.25)(73+99)69 = 11,200 miles, whereas the correct distance is 9730 miles. That 13% error is large. – whuber Apr 08 '13 at 17:22

score 0 · Answer 2 · edited Apr 13 '17 at 12:34

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Are you familiar with python? If you are there's another post which covers your Question!

What tools in Python are available for doing great circle distance + line creation?

edited Apr 13 '17 at 12:34

Community

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answered Apr 08 '13 at 13:09

nickves

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Getting a "square" of lat/lon for database query

2 Answers2