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map-hst.txt
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1995-08-20
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Map-HST.txt ver 7.2e MAP MAKING FROM TRACK HIST FILES
The APRS mapmaking program MAPFIX can overlay any APRS track history
file onto a working map. You can then use the cursor to draw in roads
over the track history points. Since the track history points were taken
at regularly timed intervals, you should 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.
Recently, I have added the F8 key which is a FIX-NOW command. This
permits you to override the regular timing of GPS fixes, and force a GPS
fix at any time by simply pressing F8. 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.
This is so you get a steady stream of fixes.
2) Everytime you want to mark an intersection or checkpoint or other
feature, press F8 to instantly update your GPS position. This
will assure that you get a fix at that location.
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.
Usually it is easy to remember these marks, since you probably
already have a paper map for the special event for reference.
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.