MILEMARK.TXT      INTERSTATE MILEMARKERS
Document version: 8.6.2
Document dated:   Dec 03 (previous was 30 Aug 2002
Author(s):        Bob Bruninga, WB4APR 
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INTRODUCTION:  Prior to APRS, Mile markers were and remain the universal 
mobile radio position location system for all 2-way radio users and
services.  I consider Milemarks to be a manditory requirement in all APRS
systems though it was not in the spec.  By using this feature built in to
APRS, you can easily locate someone simply by reference to their Milemark.

APRSdos uses the MM-DATA.DAT file which has all the milemarks in the 
Interstate Highway system.  The data is stored as straight line segments 
between two mile markers.  APRSdos uses these to interpolate the location
of any mile marker in between.  Only California is excluded 
because it has no state-wide MM system (at this time)...

In versions prior to 860, APRSdos only used the LATITUDE for north-south
segments and LONGITUDE for east-west segments.  To display the location
it would just draw a horizontal or vertical line and the location of the
milemark is the intersection of the line and the road.  After version
860, APRSdos draws a 1 mile ambiguity circle in the vicinity of the
mile marks every 2nd, 5th or 10th mile mark depending on Range Scale.

USAGE:

The Command in APRSdos was MILE-MARK-VA95-114 for example to locate the
location of MM-114.  But in APRSdos version 861, this was further
simplified to just MM-VA95 to identify Virgina I-95, and now it simply
draws a Mile Mark circle every Nth mile so that you can see them all at
once.  This is useful for not only fine-tuning the database itself,
but also is shorter and lets you see where a mobile is without actually
having to enter his mile mark...

The OLD format is in MILEMARK.DAT.  Version 861 used a temporary format
in MM.DAT but the new simplified file format in version 862 with LAT/LONG
for each segment is in the MM-DATA.DAT file and is of the form:

     SS##,MK,LAT,LON

Where the SS## identifies the interstate or road (it is a variable length
string, so "FL5" or "GA985" are valid) and the next fields give a mile
mark and its LAT/LONG.  Since the intent of this system is only to locate
mile marks within about a mile, the file does not try to follow every
single bend in the road but just the general trend of the road.  So,
concentrate on building the data for the long straight stretches
and dont worry about the nooks and crannies.  I only used 9 entries
for the 400 miles of I-40 through the length of Tennessee..

MISSING DATA:

I have built the entire database for all states with mileage exits
since I could get the data from a Highway map, but I need help in
those states that dont have mileage exits.  Here are the states I
cannot do just from maps.  I need LAT/LONG of the key mile markers:

 MA, ME, NH, PA, and NY interstates 81, 88, and 390
 In CT, still need I395 at route 2 Norwich
                   I395 at rt 138 or 164
                   I395 at Mass State line
                   I95  at RI state line

Note, in NY, the I-87 portion of the NY State Throughway is called
NYST to distinguish if from NY87 where mile mark 0 restarts.

If  you see significant errors in the database in your area, please
let me know.

The program MILEMARK.EXE will read the MM-DATA.DAT file and plot the
resulting map.  It should look like an interstate map of the USA to
make sure it has all the data elements in the right place.

APRS-Touch-Tone MILE MARKS USING THE FILE MM-TT.DAT
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Mile marks have also been added to APRStt so that touch-tone users may
place themselves on the map anywhere with only a few digit entry.  This
is what drove me to convert from the line-intersection method to the
ambiguity circle display now in MM-DATA.DAT.

But since APRStt is purely a simplex or one repeater system it is therefor
only a local system, and there is no need to include the STATE abbreviation
in each road name.  So for APRStt, the local APRS-tt SYSOP has to trim
down the MM-DATA.DAT file to only the Interstates in range and the state
abbreviations are removed, so that VA95 becomes just "95" for example.
He should save the trimmed file as MM-TT.SSn for his backup copy and then
copy it to the generic name of MM-TT.DAT so that APRS-tt can find it.

In APRStt, the DTMF entry MMRD#nn will place a station on the map in the
vicinity of mile mark nn on road RD.  Even with the state abbreviation
removed, there is no ambiguity because mile marks always go from west to
east and south to north.  So the end of the interstate in one state and
beginning in the next are always significantly different milemark numbers.
Thus the data base at any single APRS-tt application can easily
differentiate between the two.

If you make refinements to MM-DATA.DAT, please let me
know so I can update the master files.

de WB4APR, Bob

