How to compute hypotenuse and bearing

问题

I got the below code from @DanS at this link how-to-display-a-map-still-image-file-with-a-moving-current-location

onCurrentPosition(Location current){
    double hypotenuse = upperLeft.distanceTo(current);
    double bearing = upperLeft.bearingTo(current);
    double currentDistanceX = Math.cos(bearing) * hypotenuse;
    //                     "percentage to mark the position"
    double currentPixelX = (currentDistanceX / upperLeft.distanceTo(lowerRight) * Math.cos(upperLeft.bearingTo(lowerRight))) * mapWidth;

    moveIndicatorX(currentPixelX);
}

Here are the values:

current: 41.850033,-87.65005229999997
upperLeft: 41.866514127810355,-87.6720142364502
lowerRight: 41.83397145565242,-87.62824058532715
mapWidth: 512 x 512 px

Here are the calculator online for Location, hypotenuse(Distance), bearing(Azimuths)

convert LatLng to Location format(e.g. 41° 51′ 59.45″ N 87° 40′ 19.25″ W)
compute distance & azimuths from the given Location

I got the results of:

hypotenuse = 2581
bearing = 135.21
currentDistanceX = -2562
currentPixelX = 311.9

Would like to ask you guys to:

to confirm if my computed results are correct.
on how to compute the currentPixelY (the another one point)?

By the way, I am planning to use that to compute the location of a given real life LatLng(current) against with my still image map which bonded the upperLeft and lowerRight corners of the still image into real life LatLng.

If you want to see the actual & expected output and want to easily understand the whole picture. Please refer to this link -> How to mark the current location into a still image map

回答1:

This is the actual code I'm using, not pseudo code posted previously:

Location upperLeft = new Location("");
upperLeft.setLatitude(41.866514127810355);
upperLeft.setLongitude(-87.6720142364502);
Location lowerRight = new Location("");
lowerRight.setLatitude(41.83397145565242);
lowerRight.setLongitude(-87.62824058532715);
Location current = new Location("");
current.setLatitude(41.850033);
current.setLongitude(-87.65005229999997);
double hypotenuse = upperLeft.distanceTo(current);
double bearing = upperLeft.bearingTo(current);
double currentDistanceX = Math.cos(bearing * Math.PI / 180.0) * hypotenuse;
//                     "percentage to mark the position"
double totalHypotenuse = upperLeft.distanceTo(lowerRight);
double totalDistanceX = totalHypotenuse * Math.cos(upperLeft.bearingTo(lowerRight) * Math.PI / 180.0);
double currentPixelX = currentDistanceX / totalDistanceX * 512;

System.out.println(currentPixelX); // 259.3345493341548

Your calculated answer looks a bit off. To calculate Y change copy all the X marked calculations and variables to use Math.sin() instead of Math.cos().

来源：https://stackoverflow.com/questions/7118001/how-to-compute-hypotenuse-and-bearing

标签

android

geolocation

imagemap

bearing

hypotenuse