marked a waypoint which was stored as number 206. Some GPS models allow you take an 'average' point. This will take multiple GPS points and then average all the points, in theory creating a more accurate waypoint. Usually this is used when accuracy is higher priority with the data collection and time isn't as much as a factor but this can still be done quickly.
Use a notepad, or dictating-machine, to record what that waypoint corresponds to. Although it's usually possible to type this information into the GPS itself, it can be very fiddly.
For special needs you may want to upload the waypoints to the osm traces server.
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.)
- Start collecting GPS points for your waypoint and give it some kind of recognizable ID like CT1 (Cell Tower 1). This is a good opportunity to use the average waypoint feature (that is included in a lot of GPS units) since the next steps will take a minute or so to complete.
- Use your compass to sight the structure and then record the bearing (azimuth) from your current location to the structure in your notebook.
- If you have a range finder, shoot the structure and record the distance to it in your notebook. Estimate the distance if a range finder isn't available.
- End GPS data collection and save your waypoint.
An example format to record this information in your notebook:
- CT1 = 90m @ 340° from WP1
- CT2 = 60m @ 176° from WP2
When you get back to your computer you can download your waypoints and enter your offset notes into a spreadsheet. For less accurate coordinates of these structures, you can use the measure tool included in a lot of mapping programs to measure the distance and bearing. Then place the point referring to your notes about the waypoint offset information.
For highly accurate coordinates of the structure using this offset information, you can use commercial GIS programs like ESRI Arcmap + COGO Extension or Softree Roadeng(Survey). There also exist free utilities to accurately calculate a new coordinate from distance and azimuth, for example Mentor Forward/Inverse or FizzyCalc.
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.
Main article: Photo mapping
Digital cameras are useful for recording street names, village names, and other features. Because digital photographs are timestamped, we can find out where the photographer was at the time (using their GPS log), and mark that as the photograph location.
In the example here, we might put a postbox on the map, wherever the GPS was at 4:48 pm.
Alternatively, you can use specialized software that will correlate your GPS log to your photos. The GPS information will be added to the metainformation inside the images (most commonly, the EXIF metainfo inside JPGs). That way, you can programmatically have a list of places where you took a photo. OSM software such as JOSM includes support for these "geocoded photographs".
Some software, e.g. TrekBuddy allows one to associate a photograph with a waypoint. This is understood correctly by JOSM.
When geocoding photos, be sure that the camera is in sync with the GPS time (test it before trekking!); otherwise the correlation will be displaced.
- See also: Wikipedia article on geocoded photos
Hand-drawn maps of city streets
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how this is different from walking papers? redlink was here for