Member Avatar for mappersas

I could use some assistance
My final project in a python class is to calculate the distance between 2 lat/long points. My code is really just managing the input & output portions, while using existing code (properly credited) in a function to do the actual calculations.
I've got it working using 1 type of calculation (Haversine), but I want to use a different formula, as they give slightly different results. Having said all that - my problem is - the only source I can find for the calculation I want is written in JavaScript.
Im just starting to wrap my brain around Python & Im not good enough at math to figure out what is calculation and what is JavaScript syntax..

Does anyone know a source for Rhumb Line distance calculation in Python or
Does anyone know a tool that works for doing the translation, or
Can anyone help me with the translation?

Sorry for being so long winded.

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Member Avatar for jcao219

Javascript isn't too hard to understand.
Perhaps you can give us the javascript code.

Member Avatar for jcao219

http://www.movable-type.co.uk/scripts/latlon.js

That is the js?

If you study the .rhumbDistanceTo method, that should give you an idea.
You can use the math module for sin, log, PI, etc

Edited by jcao219 because: n/a
Member Avatar for mappersas

OK there are a couple of different functions I need, so here's the whole thing

# Given a start point and a distance d along constant bearing ?, this will calculate the destination point. If you maintain a constant bearing along a rhumb line, you will gradually spiral in towards one of the poles. 
# Latitude/longitude spherical geodesy formulae & scripts (c) Chris Veness 2002-2010
# http://www.movable-type.co.uk/scripts/latlong.html
Def rhumbLine:
     # Returns the distance from this point to the supplied point, in km, travelling along a rhumb line *
     # see http://williams.best.vwh.net/avform.htm#Rhumb *
     # input   tLatLon Latitude/longitude of destination point
     # returns Distance in km between this point and destination point

     LatLon.prototype.rhumbDistanceTo = function(point) 
     var R = this._radius
     var lat1 = this._lat.toRad(), lat2 = point._lat.toRad()
     var dLat = (point._lat-this._lat).toRad();
     var dLon = Math.abs(point._lon-this._lon).toRad();
     var dPhi = Math.log(Math.tan(lat2/2+Math.PI/4)/Math.tan(lat1/2+Math.PI/4));
     var q = (!isNaN(dLat/dPhi)) ? dLat/dPhi : Math.cos(lat1);
     # E-W line gives dPhi=0
     # if dLon over 180° take shorter rhumb across 180° meridian:
     if (dLon > Math.PI) dLon = 2*Math.PI - dLon;
     var dist = Math.sqrt(dLat*dLat + q*q*dLon*dLon) * R;
     return dist.toPrecisionFixed(4);#// 4 sig figs reflects typical 0.3% accuracy of spherical model}/**
     #* Returns the bearing from this point to the supplied point along a rhumb line, in degrees *
     #* @param   {LatLon} point: Latitude/longitude of destination point
     #* @returns {Number} Bearing in degrees from North */
     LatLon.prototype.rhumbBearingTo = function(point) {
     var lat1 = this._lat.toRad(), lat2 = point._lat.toRad();
     var dLon = (point._lon-this._lon).toRad();
     var dPhi = Math.log(Math.tan(lat2/2+Math.PI/4)/Math.tan(lat1/2+Math.PI/4));
     if (Math.abs(dLon) > Math.PI) dLon = dLon>0 ? -(2*Math.PI-dLon) : (2*Math.PI+dLon);
     var brng = Math.atan2(dLon, dPhi);
     return (brng.toDeg()+360) % 360;}/**
     * Returns the destination point from this point having travelled the given distance (in km) on the
     * given bearing along a rhumb line 

     * @param   {Number} brng: Bearing in degrees from North
     * @param   {Number} dist: Distance in km
     * @returns {LatLon} Destination point
     
     LatLon.prototype.rhumbDestinationPoint = function(brng, dist) {
     var R = this._radius;
     var d = parseFloat(dist)/R;  # d = angular distance covered on earth's surface
     var lat1 = this._lat.toRad(), lon1 = this._lon.toRad();
     brng = brng.toRad();
     var lat2 = lat1 + d*Math.cos(brng);
     var dLat = lat2-lat1;
     var dPhi = Math.log(Math.tan(lat2/2+Math.PI/4)/Math.tan(lat1/2+Math.PI/4));
     var q = (!isNaN(dLat/dPhi)) ? dLat/dPhi : Math.cos(lat1); #E-W line gives dPhi=0
     var dLon = d*Math.sin(brng)/q;
     check for some daft bugger going past the pole
     if (Math.abs(lat2) > Math.PI/2) lat2 = lat2>0 ? Math.PI-lat2 : -(Math.PI-lat2);
     lon2 = (lon1+dLon+3*Math.PI)%(2*Math.PI) - Math.PI;
     return new LatLon(lat2.toDeg(), lon2.toDeg());}
Member Avatar for mappersas

never mind the last question - figured out where the method is -
problem with trying to do 2 things at the same time

Member Avatar for jcao219

for the rhumbDistanceTo
this is basically what the javascript is doing

import math

EARTHS_RADIUS = 6371 #Earth's mean radius in km

def rhumb_distance(point1, point2, radius=EARTHS_RADIUS):
    R = radius
    lat1 = math.radians(point1[0]) #could also be point1.latitude
    lat2 = math.radians(point2[0])
    #depends on if point1 is tuple or an object you define
    dLon = math.radians(abs(point2[1]-point1[1]))
    dLat = math.radians(poitn2[0]-point1[0])

    dPhi = math.log(math.tan(lat2/2+math.pi/4)/math.tan(lat1/2+math.pi/4))

    if dPhi: #make sure its nonzero
        q = dLat/dPhi
    else:
        q = math.cos(lat1)

    if dLon < math.pi:
        dLon = 2*math.pi - dLon
    dist = math.sqrt(dLat**2 + q**2*dLon*dLon) * R
    return dist
Edited by jcao219 because: n/a
commented: Took the time to actually answer the question in a way I can understand +1
Member Avatar for mappersas

thank-you thank-you thank-you!

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