How to use the cartography.geometry.Geometry.fromWKT function in cartography

txt = line.split(',')[5][:25]
        #print txt
        bv = binary.ais6tobitvec(txt) #line[5][:19]

        # Try to throw out points as soon as possible.  Use float rather than decimal.  faster??  Maybe not
        #lon = ais_msg_1.decodelongitude(bv)
        lon = binary.signedIntFromBV(bv[61:89])/600000.0
        if lonmaxx: continue
        #print 'close1:',lon
        #lat = ais_msg_1.decodelatitude(bv)
        lat = binary.signedIntFromBV(bv[89:116])/600000.0
        if latmaxy: continue

        #print 'close2: POINT ('+str(lon)+' '+str(lat)+')'

        point = Geometry.fromWKT('POINT ('+str(lon)+' '+str(lat)+')')
        inside = point.within(poly)
        if 1==inside:
            outfile.write(line)
            count+= 1

    return count

def filter_file(infile, outfile, polygonWKT, verbose=False):
    '''
    For messages 1,2, and 3, see if the message is within the bounding box and send it to outfile if it is.

    Polygon should look something like this... 'POLYGON ((-1.0 50.5, -0.5 51.2, 0.3 50.9, -1 50.5))'

    param polygon: bounding region for the query
    type polygon: WKT polygon string
    '''

    poly = Geometry.fromWKT(polygonWKT)
    bbox = poly.envelope()
    minx = bbox.minx  # for speed, throw out points as soon as possible
    maxx = bbox.maxx
    miny = bbox.miny
    maxy = bbox.maxy

    if verbose:
        print 'minLon maxLon minLat maxLat filename'
        print minx, maxx, miny, maxy

    count = 0
    linenum=0
    for line in infile:
        linenum += 1
        if linenum%1000==0:
            sys.stderr.write('line '+str(linenum)+' -- count='+str(count)+'\n')