Map Making From Track History Files

The APRS mapmaking program MAPFIX can overlay any APRS track history file onto a working map for updating or adding map features. Since the GPS track history points were taken at regularly timed intervals, avoid the temptation to simply connect the points line-by-line, because there is no assurance that any particular point occurred exactly at an intersection or a turn in the road.

APRS has the F8 key which is a FIX-NOW command which permits you to force a GPS fix at any time. This is very valuable for making sure that you get a good GPS fix at each intersection, checkpoint or other landmark while driving and building a track history.

Here is a typical procedure for making maps from track histories:

  1. Set HSP-POSRATE to something like every 5 to 15 seconds or so.

  2. Press F8 to mark any intersections or turn points.

  3. If you want to specifically mark that point with a label, then press GO to bring the cursor to that location, and press INPUT-ADD to add an OBJECT to your POSIT file giving it the name of the location you want to remember. The INPUT-ADD command will ask you for the name of the object plus any comments.

  4. Alternatively, to avoid having to type in the name (while driving), you can just hit the INPUT-SAVE command, and a serial numbered object will be added to the position list. If you can remember what these sequential OBJects are, then unique names are not necessary.

    Unfortunately, when you replay the track history file back in MAPFIX, all the dots look the same, but at least if you used F8, one of them will correspond to each marked location. Later after you have integrated the map into APRS, then you can do a real REPLAY of the file, and these special checkpoints or marked locations WILL show up to verify the quality of the map...

    An ALTERNATIVE to step 1 and 2 above, is to set your POSRATE to 10 minutes, so that NO points go into the track history, EXCEPT for each time you press F8. This gives you total control over what dots will be overlayed in MAPFIX. In effect you are using your CAR AS A MOUSE in the real world and using F8 to "click" on each turn in the road! The down side is that this method demands a LOT of driver concentration. The UP side is that EVERY POINT was selected by you and all you need to do in MAPFIX is connect the dots!

    In my opinion, if the map is big and you are doing a lot of driving, then the automatic high 5 to 15 sec rate will allow you to think about other things while driving without fear of missing a slight turn. You can still mark any point with the F8, but the problems are figuring which dot is which when you go to build the map... So in addition to just marking an intersection, you should also be sure to eventually drive through the same intersection on the other road to clearly show where the road is.

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