Recording GPS tracks
|A good way to get involved in the OpenStreetMap project is to upload GNSS (GPS, Galileo, GLONASS, etc.) traces. Recorded by your satellite receiver or mobile phone, the typical trace is a record of your location every second, or every meter ("tracelog"). Convert it to GPX format if it wasn't done for you automatically. The collected data can be displayed as a background of thin lines or little dots within the map editor. These lines and dots can then be used to help you add map features (such as roads and footpaths), similar to tracing from aerial imagery.|
|Record||Convert||Modify tracelog||Upload||Accuracy||GPS Reviews|
Recording GPS tracks requires a GNSS Receiver (like GPS, Galileo, GLONASS, etc.) with the ability to save your location. Satellite Receiver is a device which allows you to accurately pinpoint your position, by receiving radio signals from satellites. To record tracks and/or waypoints, you will need to select a sat unit with this function — a specialized unit, but also a smartphone are both good candidates.
Types of GNSS (or satellite) receivers
There are many types of satellite receivers, from a simple logger to smartphones with embedded GNSS chip(s). The most useful for OpenStreetMap listed below.
See GPS Reviews for a list of reviews of receivers by OSM contributors.
With hundreds of receiver devices available, providing detailed instruction for all of them is infeasible. The following guide therefore provides generic advise to help you get started. Not all the steps may be necessary (or possible) on your particular device. If you need any help, please ask questions on the mailing lists or IRC.
Record the track
Go for a walk or a cycle ride or a drive (or whenever you take any kind of journey)
Frequently Asked Questions
Can I use a smartphone?
It depends. Most smartphones do include GPS receivers and you can record track logs using one of the numerous available apps. Unfortunately the accuracy between phones can vary greatly, even between models from the same manufacturer! It can be very difficult to work out the technical accuracy of a track, but a good compromise is to compare your results to other sources. Have a go at recording a track and check that it is smooth (does not jump all over the place) and is roughly in line with GPS tracks recorded by others (preferred), and/or aerial imagery (least preferred due to inaccuracy of aerial imagery in hilly areas).
Note: Recording GPS tracks on a smartphone will result in the battery running out quicker.
See Software/Mobile for a list of software for your smartphone; for most platforms there is a table comparing the "Track making features" of the apps.
One could also just take photos along the route. You may get the latitude and longitude and the original date time by reading EXIF information from photos you have taken. Generate gpx file(an xml format) either manually of by programming in the proper format for gpx file and test it by opening with JOSM to make sure the gpx file is proper formatted, and then you may be able to load gpx file using web interface or by JOSM upload plugin.
Not all car 'SatNavs' include an option to record GPS tracks, and if it does it may be within a hidden service menu. Try searching for your particular model number online or ask in the mailing lists or IRC. Be aware, that even if you can record a track, it may not be practical due to the short battery life (less than 3 hours is common if the screen remains on when recording). Furthermore, some devices have a "lock to track" mode that cannot be disabled and are only useful away from all mapped tracks or roads. To test this, walk away from a road at 45° and watch if your recorded path follows the road and then suddenly jumps away when you are several 10's of meters away.
What to record?
Anything, as long as it reflects a real world feature. For example, try to avoid tracklogs of flights, as these could be distracting or confusing to other map contributors. Don't worry if you don't have the time to edit the map features after uploading a GPS track - the track on its own is helpful for others. Also tracklogs of roads that have already been mapped are also useful, as they can help to validate the true path of a road by providing more sample points.
Marking unreachable objects
GPS Offset Method
(Intermediate Level Technique)
When there is a structure or object that you want to GPS but is inaccessible (like a cell tower surrounded by a large fence) then you can use the 'GPS Offset Method' to get its coordinates. To do this you will need your GPS, compass, optionally a range finder and a way to record your data like a notebook or voice recorder. (Instead of using a range finder you can just estimate the distance but this will usually be less accurate.)
Aimed straight segments method
Another method (much more simple, a little less accurate) is to "draw" two straight segments by GPS traces (walk right towards the object twice from different locations) both pointing at that distant object and then draw two lines through them. The lines will intersect in the object's location.
If the unreachable object is not critical, you can simply estimate where it should be on the map, but make sure to mark it with Key:fixme, so that others know and possibly position it better later.