# Longitude conversion according to your latitude

1. May 15, 2012

### michael atlas

I have two latitude/longitude points. They are really close together. What I want to do is find the difference between the two longitides and calculate how many yards that would be. If I did the calculation with with the two latitudes, it would be just 2025yds per minute of latitude. However, for the longitude; being that the closer you get to the poles, the closer the lines of longitude move together, you have to apply a conversion to it.

If my lat/longs were 34.34°W, 79.1°N and 34.23°W, 80.3°N Respectively, I want to find the exact amount of yards between my two lines of longitude.

If any one had the formula to find out how many yds per minute of longitude according to what latitude I am at, I would greatly appreciate it.

Thanks,
Mike

2. May 15, 2012

### Studiot

Can you not use the second formula I gave you in the other thread?

The radius of any circle of latitude (rθ) is given by the mean radius (r) of the earth times the cosine of the angle of latitude (θ)

rθ = rcosθ

And by the way what is your application here and there ?

Last edited: May 15, 2012
3. May 16, 2012

### michael atlas

My application is for sonar work, programming in matlab.

When I get the answer from the other thread... I just multiply that latitude by 2025yds per degree of latitude AND longitide?

Is that true, because of the fact that I have to convert longitude given the latitude for Theta E

4. May 16, 2012

### billiards

At what latitude? 79.1°N or 80.3°N or somewhere in the middle?

This can all be solved quite easily if you have a good grasp of spherical co-ordinates.

5. May 16, 2012

### Studiot

The difference in longitude is the distance along a parallel of latitude.

Each parallel of latitude is a circle of radius rθ = r cos(θ)

So the circumference of that parallel is 2∏rθ in yards or metres or whatever and 360 degrees in angle.

So for instance the difference between 10° west and and 20° west is 10°

So this in yards is

10/360 times circumference = (10/360) * 2∏rθ where r is the mean radius in yards.

Now the latiture you use for θ is different for each point so you should take the average latitude by adding up the two latitudes and dividing by 2.

Does this make sense?

6. May 16, 2012

### michael atlas

Yes it does.

Appreciate it.