How to do a subscriber node?

edit

I want to subscribe to the NavSatFix topic and be able to retrieve the longitude and latitude from a GPS that is publishing that infor. Here's the documentation of the message that I need to get the data from: http://docs.ros.org/api/sensor_msgs/h... I've been following the ROS tutorials to work with it but it's really barebones and I don't get how I'm supposed to get that info. This is what I have so far:

#!/usr/bin/env python
import rospy
from sensor_msgs import NavSatFix

def callback(data):
    rospy.loginfo(rospy.get_caller_id() + "I heard %s", data.data) 

def infoGetter():

rospy.init_node('infoGetter', anonymous=True)

rospy.Subscriber("sensor_msgs/NavSatFix", float64, callback)

rospy.spin()

if __name__ == '__main__':
    infoGetter()

Now I need to be able to retrieve the info the I need from the topic that is publishing the Longitude and Altitude. My main question is to know how to do that step

EDIT 1:

This is what I got from the tutorials:

#!/usr/bin/env python
import rospy
from sensor_msgs.msg import NavSatFix

def callback(data):
    rospy.loginfo("Longitude: %f, Altitude %f" % (data.longitude, data.latitude))
    longitude = data.longitude
    latitude = data.latitude
    #Call for the programName(longitude,latitude)

def infoGetter():

    rospy.init_node('infoGetter', anonymous=True)

    rospy.Subscriber("sensor_msgs/NavSatFix", NavSatFix, callback)#First parameter is the name of the topic

    rospy.spin()

if __name__ == '__main__':
    infoGetter()

EDIT 2

I finally was able to subscribe to my desired topic and get the values that I need for that topic. Now I want to send those values to another program to do some manipulation. What I did is that I made the function call inside the callback function but it only seems to "work" when I have rospy.spin() in my infoGetter function. However I don't want it to run infinitely, I just want it to run once, subscribe to the topic, get the info needed and send it to whatTheHell() to do only 1 calculation. Is there a way to just run the program once without having it looping forever and ever?

Here's my code for reference:

#!/usr/bin/env python import rospy from sensor_msgs.msg import NavSatFix from RetreiveFiles import whatTheHell

def callback(data): rospy.loginfo("Longitude: %f, Latitude %f" % (data.longitude, data.latitude)) #global latitude #global longitude latitude = data.latitude longitude = data.longitude whatTheHell(latitude, longitude)

def infoGetter(): rospy.init_node('infoGetter', anonymous=True) rospy.Subscriber("/novatel/fix", NavSatFix, callback) #rospy.spin() if __name__ == '__main__': infoGetter()