Question

I’m trying to represent a route between a number of points on a static map using an encoded polyline. The code for this is in a function called getStaticMapAddress, defined like so:

def getStaticMapAddress(self, route):
    destUser = DestUser(self.destination)
    route += [destUser]
    attempts = 0
    while attempts < 10:
        try:
            encodedPolyline = self.encodePolyLine(route)
            break
        except googlemaps.GoogleMapsError:
            print "Error. Try again"
            attempts += 1
    url = "http://maps.google.com/maps/api/staticmap?zoom="+encodedPolyline[1]+"&sensor=false&size=400x400&markers="
    i=0
    while i<len(route):
        url += str(route[i].location.lat)+","+str(route[i].location.lng)
        i=i+1
        if i < len(route):
            url += "|"
    url += "&path=color:0xff0000ff|weight:5|enc:"+encodedPolyline[0]
    return url

The route is represented as a list of User objects (of which DestUser is a subclass). The self.encodePolyLine() method is defined as follows:

def encodePolyLine(self, route):
    routePairs = []
    destUser = DestUser(self.destination)
    route += [destUser]
    i=0
    while (i < len(route)-1):
        # GET ALL TURNING POINTS FOR EACH POINT ON ROUTE, THEN PUT THEM
        # IN PAIRS AND SEND THEM TO glineenc.encode_pairs()
        for step in gmaps.directions(gmaps.latlng_to_address(route[i].location.lat, route[i].location.lng), gmaps.latlng_to_address(route[i+1].location.lat, route[i+1].location.lng))['Directions']['Routes'][0]['Steps']:
            routePairs += [(step['Point']['coordinates'][0], step['Point']['coordinates'][1])]
        i=i+1
    return glineenc.encode_pairs(routePairs)

This glineenc module is from here and takes in a list of coordinate pairs, returning a pair containing the encoded line string and an encoded string representing the maximum zoom level to be able to see all of the points. So, I have a route going between Brighton, London, Bristol and Manchester which I have passed into this function. The following URL was the output:

http://maps.google.com/maps/api/staticmap?zoom=B@@@@@?@AA@AA??A@@A@A@?@@@@@@@@B?@@@@@A@@@@@@?B@@AABABA@@@@@@@B&sensor=false&size=400x400&markers=50.8202008,-0.1324898|51.447341,-0.0761212|51.4608947,-2.5884312|53.4778853,-2.2308146|53.4778853,-2.2308146&path=color:0xff0000ff|weight:5|enc:b|XqvduHm@cDcMhAfAfFrc@{BlJgDqHaZkEy[vsKiwp@ciHahd@}nEwoK_KqB_QmoIpAyBw@Mv_BqxDmC`EasCvAeFuuAwi@_Rq|DuVnYgPdXyHvIcBcSgElgBkqBzKgh@`xD_cAzBpBvNM{HsHh]wNfbCzOxpCrUjeD_`Ahi@pItyGdXj`D_PjctLa}BzhH~nFn\dPfe@bObv@dC`i@fS_HrFk@~AmAzDsW_Ak_CmiAkuGy_GvxDctEolnBcpdEhtPc}Srp~AcvsCi_a@clJakR`]kiCr]opDtRcW}JhVcV_EmDaDhFkCc@

If you view this you can see something has gone wrong. I’m not sure exactly what has happened but I noticed that the new route appears to be a projection of the proper route, if reflected using the equator and meridian as lines of symmetry. Not sure why it would have done this, but that’s about all I can see as the possible cause of the problem. Any ideas?

Answer 1

Random guess: you’ve accidentally swapped the longitude and latitude arguments.