如何基于到点的距离来计算新的纬度

Question

I'm trying to calculate a new lat long from a point based on a distance in metres from that point.

I've found a few posts on here and elsewhere that helped, but I'm still having a little trouble.

Here's the code I've got so far:

        public LatLon CalculateNewCoords(decimal startingLat, decimal startingLon, int distanceEast, int distanceNorth)
    {
        int r = 6378137;
        decimal dLat = Convert.ToDecimal(distanceNorth) / Convert.ToDecimal(r);

        decimal pi = Convert.ToDecimal(Math.PI);
        double cosInput = Convert.ToDouble(pi * startingLat / Convert.ToDecimal(180));

        decimal dLon = Convert.ToDecimal(distanceEast) / Convert.ToDecimal(Convert.ToDouble(r) * Math.Cos(cosInput));

        decimal lat0 = startingLat + dLat * (180 * pi);
        decimal lon0 = startingLon + dLon * (180 / pi);     

        LatLon output = new LatLon();
        output.Latitude = lat0;
        output.Longitude = lon0;

        return output;
    }

The longitude seems correct, but the latitude is displaying quite significantly out.

I'm using it as follows:

CalculateNewCoords(Convert.ToDecimal(40.743461), Convert.ToDecimal(-74.175847), 0, 1000);

Can someone point out what I'm doing wrong please?

Answer 1

The error is in the first line:

    decimal lat0 = startingLat + dLat * (180 * pi);
    decimal lon0 = startingLon + dLon * (180 / pi);     

this is fore sure not correct, both lines must use the same radians to degrees conversion. Replace with 180/pi like in line 2.
further think on using double instead if decimal.