Calculate distance from a lat/lon coord to a street

Question

I have the coordinates for a street, for example:

CLLocationCoordinate2D street[3];
street[0] = CLLocationCoordinate2DMake(-17.3521, 145.5898);
street[1] = CLLocationCoordinate2DMake(-17.3518, 145.5910);
street[2] = CLLocationCoordinate2DMake(-17.3515, 145.5917);

And a location that is fairly close to the street (about 60 meters):

CLLocationCoordinate2D location = CLLocationCoordinate2DMake(-17.3525, 145.5911);

How can I calculate the distance between the location and position along the street's path?

I'm not looking for the distance to the closest point in the array, I want the distance to the closest position in between the points.

EDIT

It's easier to describe my question with a picture:

• street is the three red dots
• location is the blue dot

I want to calculate the length of the yellow line in meters.

Answer 1

Here is my attempt to solve this, but I'm not sure if it's the best way?

// http://www.cprogramto.com/c-program-to-find-shortest-distance-between-point-and-line-segment/
double FindDistanceToSegment(double x1, double y1, double x2, double y2, double pointX, double pointY)
{
  double diffX = x2 - x1;
  float diffY = y2 - y1;
  if ((diffX == 0) && (diffY == 0))
  {
    diffX = pointX - x1;
    diffY = pointY - y1;
    return sqrt(diffX * diffX + diffY * diffY);
  }

  float t = ((pointX - x1) * diffX + (pointY - y1) * diffY) / (diffX * diffX + diffY * diffY);

  if (t < 0)
  {
    //point is nearest to the first point i.e x1 and y1
    diffX = pointX - x1;
    diffY = pointY - y1;
  }
  else if (t > 1)
  {
    //point is nearest to the end point i.e x2 and y2
    diffX = pointX - x2;
    diffY = pointY - y2;
  }
  else
  {
    //if perpendicular line intersect the line segment.
    diffX = pointX - (x1 + t * diffX);
    diffY = pointY - (y1 + t * diffY);
  }

  //returning shortest distance
  return sqrt(diffX * diffX + diffY * diffY);
}

-

CLLocationCoordinate2D street[3];
street[0] = CLLocationCoordinate2DMake(-17.3521, 145.5898);
street[1] = CLLocationCoordinate2DMake(-17.3518, 145.5910);
street[2] = CLLocationCoordinate2DMake(-17.3515, 145.5917);

CLLocationCoordinate2D location = CLLocationCoordinate2DMake(-17.3525, 145.5911);


CLLocationDegrees distanceDegrees = CGFLOAT_MAX;
for (NSUInteger nodeIndex = 1; nodeIndex < 3; nodeIndex++) {
  CLLocationCoordinate2D nodeCoord = street[nodeIndex];
  CLLocationCoordinate2D prevNodeCoord = street[nodeIndex - 1];

  CLLocationDegrees distanceToCurrent = FindDistanceToSegment(prevNodeCoord.longitude, prevNodeCoord.latitude, nodeCoord.longitude, nodeCoord.latitude, location.longitude, location.latitude);

  if (distanceToCurrent < distanceDegrees)
    distanceDegrees = distanceToCurrent;
}

CLLocationDistance distance = distanceDegrees * 111111; // 1.0 degree is approximately 111,111 meters

NSLog(@"%f", distance);  // 78.15 meters

Answer 2

Take a look at this site: link.

It shows different types of distance measuring with latitude and longitude coordinates and even some code examples (in javascript).

Answer 3

If you have the find the crow distance between two locations, make CLLocation object of two coords, then

CLLocationDistance meters = [newLocation distanceFromLocation:oldLocation];

and if you have find the actual road distance divide the two coords to several coords in straight line and find the distance and add them up.