CODEWITHSUNDEEP
google-mapsgpsgeography
CBK
CBK

Reputation: 190

Calculate shortest distance between a GPS coordinate and a route

Is there a simple way to calculate the closest distance between a route (directions between two cities for example) and a GPS coordinate using the Google Maps API?

One appoach I can think of is to translate the route into a set of GPS coordinates and calculate the distance to each coordinate. Is there a better way of doing this?

Upvotes: 0

Views: 2094

Answers (1)

AlexWien
AlexWien

Reputation: 28727

One appoach I can think of is to translate the route into a set of GPS coordinates and calculate the distance to each coordinate. Is there a better way of doing this?

Yes there is a much better way.
The first part is correct: translate to a polyline of lat/lon coordinates. However the second is to simple. You want the shortest distance to the line segment not the the next corner point, that is the start or end of the line.

In school you used the hessian normal distance. However this formula calculates just the distance to an infinite line. In case of a polyline you have an sequence of line segments.

So you need a formula for "distance to line segment". This one you can find using that search terms.

Having this formula implemented, you interate over all line segments each defined by two points (polyPoint[i], polyPoint[i+1]) and take the minimum of the distance.

Don't forget to transform the current line segement to cartesian (x,y) space, because the usualy formulas, do not work on spehrical coordinates.

This approach is more complex, but gives exact results. Remember a line on a route if often 400-700 meters long. So the simple approach you asked, gives in this case an error of 200-350m if you are in the middle between the two points.

Upvotes: 2

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