Calculating new coordinates using distance/heading

[+zeebob]

Hi All,

 

I am trying to determine the final coordinates of a multi-cache using a heading and distance I have worked out from the clues.

 

Example: I need to travel 230m heading 179° true from a set of GPS coordinates.

 

The cache I am trying to find is impossible to locate by walking in a straight line on that heading for that distance so I need to work out the coordinates. How do I calculate this best?

[+stijnhommes]

Most GPS units and smart phone apps have the ability to calculate this automatically, so you might simply have to have a rummage around your phone or GPS unit to find it. If all else fails, you can use Google Earth to measure the required amount into the right direction and see where you end up.

[+ngrrfan]

It is called "Projecting a point". If you are using a GPS, most of them have the capability to do this function. What it will do is exactly what you are asking.

[+Cardinal Red]

It is called "Projecting a point". If you are using a GPS, most of them have the capability to do this function. What it will do is exactly what you are asking.

 

If you encounter a distance and direction projection out in the field, that is your solution. But if you have that information while at your Windows computer, this could be an easier solution. Or just a double check. FizzyCalc

[+redwoodkestrel]

It is called "Projecting a point". If you are using a GPS, most of them have the capability to do this function. What it will do is exactly what you are asking.

 

If you encounter a distance and direction projection out in the field, that is your solution. But if you have that information while at your Windows computer, this could be an easier solution. Or just a double check. FizzyCalc

 

Or if you have a smart phone in the field you can use the GeoCache Calculator... just be sure to download the app before heading out when you're sure you have a connection. Then you can use it while out caching regardless of if you have reception or not.

 

And like others have said, many GPS units have the ability to project a waypoint as well- another solution if you're trying to do it in the field.

[+zeebob]

Thanks for the tips. A quick look on the App Store and I found GeoTools that has a 'project coordinates' function that achieves this. I couldn't find any other apps or the ability in the Groundspeak Geocaching app to do this.

[+SSO JOAT]

Try this...

 

φ2 = asin( sin(φ1)*cos(d/R) + cos(φ1)*sin(d/R)*cos(θ) )

λ2 = λ1 + atan2( sin(θ)*sin(d/R)*cos(φ1), cos(d/R)−sin(φ1)*sin(φ2) )

 

where φ is latitude, λ is longitude, θ is the bearing (in radians, clockwise from north), d is the distance travelled, R is the earth’s radius (d/R is the angular distance, in radians)

For final bearing, simply take the initial bearing from the end point to the start point and reverse it (using θ = (θ+180) % 360)

 

Easy as π

 

You could also just switch your GPS to UTM and take the grid coordinates and apply the Pythagorean theorem. At short distances, you really don't have to worry about the Great Circle effects.

Edited May 29, 2013 by SSO JOAT

[+fizzymagic]

You could also just switch your GPS to UTM and take the grid coordinates and apply the Pythagorean theorem. At short distances, you really don't have to worry about the Great Circle effects.

 

Don't do this. UTM northing can be up over 2 degrees off of true north, so it gives the wrong answer unless you are close to the center of a UTM zone. Which you probably are not.

Edited May 29, 2013 by fizzymagic

[+SSO JOAT]

Naw, you just need to know the declination difference between the 2 maps (lat/long vs UTM). It's printed on your local USGS map. There's a grid north, true north, and magnetic north.

[+Trucker Lee]

I haven't been able to master projecting, usually just mark where I am and go exploring until I arrive at a location the reverse of the projection. 180 ft on heading 110 is the same point as 180 ft at bearing 290.

[+SSO JOAT]

Just pick the waypoint you are at (or record a new one where you're standing) and hit the menu button. Select "Project Waypoint" from the list. Enter the bearing and distance and it will make the point you need to go to. Couldn't be many things that are easier.