# math

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If I have a known point, then have a direction in degrees minus declination and a distance, how do I find the grid or new coord's? I think there is a formula but I can't recall it. Any help would help. -SineMora-

I think you're looking for the "great circle" formula. There's another (supposedly easier?) way to do it, but I can't recall the name right now.

--

Pehmva!

Random quote:

Try Ed Williams web site. I'm sure this will answer your question.

"Every cache has it's rightful place."

quote:
Originally posted by -SineMora-:

If I have a known point, then have a direction in degrees minus declination and a distance, how do I find the grid or new coord's? I think there is a formula but I can't recall it.

The answer depends on a lot of things. Do you want an accurate result, or are you willing to approximate the Earth as a sphere? For magnetic headings of relatively short distances (less than 1 km or so) then the spherical approximation is probably OK, and there is a formula, which you can find at the Aviation Formulary.

For accurate calculations using the ellipsoidal model of the Earth, there is no closed-form equation. The calculations are done iteratively. You can try my program GeoCalc, which does those calculations.

Since the probability that you do have access to a GPS unit is high, considering that you are writing in this forum, you have an excellent tool there.

The GPS can be used as a calculation device too, for solving problems like this.

Enter the coordinates of the known point as a waypoint. Then project a new waypoint in the desired direction, at the distance in question, and it will calculate the new position for you.

Anders

quote:
Enter the coordinates of the known point as a waypoint. Then project a new waypoint in the desired direction, at the distance in question, and it will calculate the new position for you.

I don't know 'bout other GPSr's,

but

the SporTrack does that: go to the position screen,

next choose "projection"

fill in the distance and degrees (angle)

and the answer comes as a projected waypoint.

um yeah...I thought I was reasonably intelligent until I read this thread.

I was wrong.

Life is 10% what happens to you and 90% how you react to it.

assuming "declination" means magnetic declination and "direction in degrees minus declination" means true bearing...

delta x = r cos theta

delta y = r sin theta

latitude scales constantly to distance

longitude scales to distance as the cosine of latitude

hth

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