Template:Great circle distance/er

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Usage

{{Great circle distance/er|latitude}}

Calculates the Earth's radius, in kilometers, at a given latitude. Uses the following formula:

<math>R=\sqrt{[(r_1^2*\cos{B})^2+(r_2^2*\sin{B})^2]/[(r_1*\cos{B})^2+(r_2*sin{B})^2]}</math>

with latitude <math>B</math>, radius <math>R</math>, radius at equator <math>r_1=6378.137</math>, and radius at pole <math>r_2=6356.752</math>

With no latitude input, it defaults to the mean Earth radius.