WaypointConvert.py

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# Taylor Pool
# December 1, 2016
#AUVSI Project

# This script contains a function that converts given GPS coordinates into waypoints for ROS.
#The input supports two types of GPS coordinates
#1) Long Degree Decimal Format
#       ex: -34.6830975
#2) Degrees-Minutes-Seconds Format
#       ex: N78-45-76.23
#The function to be called for conversion is to_meters(originLat, originLong, originAlt, newLat, newLong, newAlt, flag)
#The two formats listed above can be used simultaeously in the same function call.
#NOTE: Degrees-Minutes-Seconds Format is the only format that uses NSEW directions in front.
#NOTE: Degrees-Minutes-Seconds Format needs to be surrounded with quotations when passed as an argument.

from math import pi
from math import cos
from math import sqrt

#constant
EARTH_RADIUS = 6371008.0                                                        #in meters

#Function decimal_degrees
#Pre: string is in format [N/E or S/W]DD-MM-SS.SS
#Post: Returns GPS component in long decimal format
def decimal_degrees (string):
        a = 0

        firstLetter = string[0]
        if firstLetter == 'N' or firstLetter == 'E':
                a = 1
        elif firstLetter == 'S' or firstLetter == 'W':
                a = -1

        lessString = string.strip("NSEW ")

        values = lessString.split('-', 2)

        d = float(values[0])
        m = float(values[1])
        s = float(values[2])

        decimal = a*(d+(m/60.0)+(s/3600.0))

        return decimal


#Function meter_convert
#Takes in long decimal GPS format and outputs the destination in meters
#Pre: Lat and Long are given in decimal degrees, and altitude is in meters
#Post: Returns destination in tuple format [latChange, longChange, newAlt, distance]
def meter_convert(originLat, originLong, originAlt, newLat, newLong, newAlt):

        #Find CrossSectional Radius of Earth for Given Latitude Degree
        crossRadius = cos(originLat*pi/180.0)*EARTH_RADIUS

        GPSdestination = [newLat, newLong, -newAlt]     #Given in terms of N, E, D

        #Convert Change in GPS Coordinates to Change in Meters
        latChange = ((newLat - originLat)*pi/180.0)*EARTH_RADIUS                #in meters

        longChange = ((newLong - originLong)*pi/180.0)*crossRadius

        altitudeChange = newAlt - originAlt

        #Compute Total Distance to Fly
        distance = sqrt(pow(latChange, 2.0) + pow(longChange, 2.0) + pow(altitudeChange, 2.0))

        #New Waypoint Given in Terms of [North, East, Down]. In meters.
        destination = [latChange, longChange, newAlt, distance]

        return destination


#Function to_meters
#Pre: input of all the data needed to fly to a waypoint
#flag: tells whether altitude is in meters or feet
#               0: meters               else: feet
#Post: outputs destination given in meters that ROS can understand.
def to_meters(originLat, originLong, originAlt, newLat, newLong, newAlt, flag):

        #Altitude in Feet needs to be converted to Meters
        if (flag != 0):
                originAlt = .305*originAlt
                newAlt = .305*newAlt

        GPSorigin = [originLat, originLong, originAlt]
        GPSdestination = [newLat, newLong, newAlt]

        values = [str(originLat), str(originLong), str(newLat), str(newLong)]
        newValues = []

        for value in values:
                if ("N" in value) or ("S" in value) or ("E" in value) or ("W" in value) == 1:
                        #print "Degrees Minutes Seconds Format"
                        #print value
                        newValues.append(decimal_degrees(value))
                        #print decimal_degrees(value)
                else:
                        #print "Long Decimal Format"
                        newValues.append(float(value))

        destination = meter_convert(newValues[0], newValues[1], originAlt, newValues[2], newValues[3], newAlt)

        #Test Output
        #print("Origin in GPS Coordinates: " + str(GPSorigin))
        #print("\n")
        #print("Destination in GPS Coordinates: " + str(GPSdestination))
        #print("\n")
        #print("Destination Coordinates (Meters) with Distance: " + str(destination))

        return destination






#Test
#test = to_meters("N90-90-76.45", "W45-67-23.54", 20.0, -40.257049176511316, 111.65421836078167, 20.0, 0)

#if __name__ == __main__:
#       toMeters(40.25787274333326, -111.65480308234692, -20.0, 40.257049176511316, -111.65421836078167, -20.0, 0)




#Sample Output:
#tpool2@FB280-09:/media/tpool2/TAYLORPOOL/AUVSI/rosflight_utils/src$ python WaypointConvert.py
#Degrees Minutes Seconds Format
#N90-90-76.45
#91.5212361111
#Degrees Minutes Seconds Format
#W45-67-23.54
#-46.1232055556
#Long Decimal Format
#Long Decimal Format
#Origin in GPS Coordinates: ['N90-90-76.45', 'W45-67-23.54', 20.0]


#Destination in GPS Coordinates: [-40.257049176511316, 111.65421836078167, 20.0]


#Destination Coordinates (Meters) with Distance: [-14653095.165621338, -465750.5181201244, 20.0, 14660495.267141715]