Distance along a line

distance_along_line.py

"""
Use https://github.com/jklymak/waypoint_distance instead!
"""

def get_xy(ds, lat0, lon0):
    x = (ds.longitude - lon0) * np.cos(np.deg2rad(lat0)) * 60 * 1.852
    y = (ds.latitude - lat0) * 60 * 1.852
    ds['x'] = x
    ds.x.attrs['units'] = f'km east of {lon0}'
    ds['y'] = y
    ds.y.attrs['units'] = f'km north of {lat0}'
    return ds

def dist(x1,y1, x2,y2, x3,y3): # x3,y3 is the point
    px = x2-x1
    py = y2-y1

    dsq = px*px + py*py

    u =  ((x3 - x1) * px + (y3 - y1) * py) / dsq

    if u > 1:
        u = 1
    elif u < 0:
        u = 0

    x = x1 + u * px
    y = y1 + u * py

    dx = x - x3
    dy = y - y3

    dist = np.sqrt(dx*dx + dy*dy)

    return dist

def get_alongx(wps, x, y):
    
    distline = np.zeros(len(wps)-1)
    
    for j in range(1, len(wps)-1):
        distline[j] = np.sqrt((wps[j-1][0] - wps[j][0])**2 + (wps[j][1] - wps[j-1][1])**2)
        
        
    ind = np.zeros(len(x))
    for j in range(len(x)):
        thedist = np.Inf
        for i in range(len(waypoints)-1):
            dd = dist(wps[i][0], wps[i][1], wps[i+1][0], wps[i+1][1], x[j], y[j])
            if dd < thedist:
                thedist = dd
                ind[j] = i
    
    alongx = x * 0.
    for i in range(len(x)):
        # get the distance along the line....
        indd = int(ind[i])
        x0 = wps[indd][0]
        x1 = wps[indd+1][0]
        y0 = wps[indd][1]
        y1 = wps[indd+1][1]

        xp = x[i] - x0
        yp = y[i] - y0
        dot = xp * (x1 - x0) + yp * (y1 - y0)
        dot = dot / np.sqrt((x1 - x0)**2 + (y1 - y0)**2)
        
        alongx[i] = dot + distline[indd]
    return alongx