ftp.barnyard.co.uk/2015.02.ftp.barnyard.co.uk.tar/ftp.barnyard.co.uk/cpm/walnut-creek-CDROM/SIMTEL/CPMUG/CPMUG033.ARK/N-ELT1.DOC

Text File | 1984-04-29 | 6KB | 116 lines

GENERAL COMMENTS CONCERNING THE PROGRAM "N-ELT 1":

COL BOB MATTSON
HQ CAP

DEAR BOB:
     ENCLOSED IS A COPY OF THE ELT DIRECTION FINDING ASSISTANCE PROGRAM WHICH
WE PLAN TO USE ON THE NELT SEARCHES. NO GREAT SHAKES, BUT IT IS ABLE TO PROVIDE
SOME SIMPLE STATISTICS AND ACCESSORY FUNCTIONS.

     I AM REASONABLY CONFIDENT THAT THIS PROGRAM IS CORRECT IN WHAT IT DOES,
AS WE HAVE TESTED IT AND UNDER MOST CONDITIONS IT WILL PERFORM WELL.

     A COUPLE OF COMMENTS ARE IN ORDER, THOUGH.
       1) THE CROSSINGS OF BEARINGS (CUTS) ARE CALCULATED BY SIMULTANEOUS
SOLVING OF THE EQUATIONS FOR A LINE (SLOPE-INTERCEPT VERSION: Y=MX+B, WHERE 'M'
IS THE SLOPE, 'B' IS THE Y AXIS INTERCEPT).  SINCE THE SLOPE OF A LINE IS
INFINITE WHEN THE LINE OF BEARING IS 0 DEGREES(360) OR 180 DEGREES, THE PROGRAM
CALLS THESE 359.9 AND 179.9 DEGREES RESPECTIVELY.  THE ERRORS SO INTRODUCED
SHOULD BE NEGLIGIBLE.
       2) AT TIMES RICK HAS SEEN ZERO DIVIDE IN THE PROGRAM, THOUGH HE HASN'T
GIVEN ME DETAILS (LINE NUMBER ETC).
       3) THE PROGRAM FLAGS ANY CUTS WHOSE COMPONENT BEARINGS ARE LESS THAN
ABOUT 30 DEG (TAN<.5) SINCE LARGE ERRORS ARE POSSIBLE WITH THESE CLOSE ANGLES.
IT SHOULD BE EMPHASIZED THAT IT IS DANGEROUS TO DISCARD ANY DATA AT ALL,
SINCE ONE CANNOT BE SURE THE ACCURACY WOULD INCREASE JUST BECAUSE THE BEARINGS
AGREE BETTER.  THE WARNING IS TO (1) ALLOW THE USER TO KNOW HIS DATA IS OF THIS
NATURE AND (2) RECOMPUTE AND TOSS OUT CUTS JUST TO SEE HOW THESE CUTS AFFECT
THE RESULT.
       4) THE PROGRAM IS FOR ASSISTANCE IN DIRECTION FINDING, AND IS ONLY ONE
OF SEVERAL TOOLS WHICH SHOULD BE USED TO PLAN THE SEARCH.  THERE MUST BE A MAP
(WITH X-Y OVERLAY GRID) AND MANUAL EVALUATION OF THE RESULTS BY THE USER
(COORDINATOR) TO FIT THIS DATA BACK INTO THE REAL WORLD (MOUNTAINS, HOUSES,
REFLECTIONS OF SIGNAL AND PROPAGATION CONDITIONS).
       5) THE RESULTS ARE ONLY AS GOOD AS THE DATA ENTERED. IF THE TEAM IS
UNABLE TO OPERATE ITS DF GEAR, OR THE COORDINATOR DOESN'T TAKE REFLECTIONS AND
OTHER CONDITIONS INTO ACCOUNT, ALL IS FOR NAUGHT.  THE BEARINGS SHOULD BE
TAKEN WITH PROVEN ACCURATE GEAR, FAMILIAR USERS, AND FROM THE BEST AVAILABLE
SITES. THERE IS NO SUBSTITUTE FOR PRACTICE AND EXPERIENCE.

     HOPES FOR THE FUTURE INCLUDE A MORE COMPLETE STATISTICAL ANALYSIS OF THE
DATA, MASSAGING IT FOR A BETTER ESTIMATE.  EXPERIENCE WILL TELL US HOW TO
DO THIS AS WE GO ALONG.

                    ENJOY - CHRIS


DESCRIPTION OF THE 'N-ELT 1' PROGRAM.

LINE #        DESCRIPTION
10-640        INITIALIZATION, COMMENTS, MENUE
650-710        DISPATCH TABLE FROM MENUE
720-880        DATA ENTRY, SLOPE & INTERCEPT CALCULATION
890-1080    CALCULATION OF CUTS
1090-1230    CALCULATION OF MEAN FIX X,Y
1240-1640    CALCULATION OF PROBABILITY ELLIPSE
1650-1920    FIND FIELD TEAM VIA BEARINGS TO KNOWN LANDMARKS
1930-1970    CHANGE PROBABILITY CONTOUR
1980-2260    EDIT BEARING TABLE
2270-2340    DECISION ON CLOSE BEARING CUTS
2350-2760    BASELINE AVERAGING CODE
2770-2790    CHANGE DECLINATION




USERS GUIDE TO 'N-ELT 1'

1) RUN THE PROGRAM

2) WHEN MENU APPEARS, CHOOSE AN OPTION OR ELSE CARRIAGE RETURN WILL ENTER YOU
   TO DATA ENTRY PORTION OF PROGRAM.  WHEN DECLINATION IS ASKED FOR, ENTER
   THE CORRECTION OF MAGNETIC FROM TRUE BEARINGS, IF USER WILL BE ENTERING
   MAGNETIC BEARINGS.  ENTER A WEST MAGNETIC VARIATION AS A NEGATIVE NUMBER
   AND EASTERLY VARIATION AS A POSITIVE NUMBER.

3) THE PROGRAM WILL ASK FOR DATA, AND THE USER SHOULD ENTER DATA WITH X FROM
   -50 TO 50,PREFERABLY FROM 0 TO 20 BUT REAL NUMBERS ARE OK, SO A MAP COVERING
   5 MILES SQUARE, DIVIDED INTO 20X20 INCREMENTS, EACH INCREMENT FURTHER
   DEVIDED BY SUB-INCREMENTS OF 10 GIVES YOU 40,000 CELLS.  IF THE X INPUT IS
   GREATER THAN 50, THE MENU IS REDISPLAYED AND COMMANDS MAY BE GIVEN.  IF THE
   X OR Y DATA IS INCORRECTLY ENTERED, THE INPUT MAY BE CANCELLED BY ENTERING
   A BEARING ANGLE OF 360 OR GREATER.

4) WHEN 2 OR MORE BEARINGS ARE ENTERED, THE PROGRAM WILL CALCULATE CUTS AND
   DISPLAY THEM. WHEN 3 OR MORE CUTS ARE OBTAINED, THE PROGRAM WILL COMPUTE THE
   MEAN OF THE CUTS AND THE PROBABILITY CONTOUR ELLIPSE SIZE.
   THE ELLIPSE IS DESCRIBED AS FOLLOWS:
    THETA=ANGLE(SK) OF SKEW FROM 0 DEGREES(DUE NORTH) OF THE 'A' AXIS
    SKEW=THE TILT OF THE ELLIPSE
    A=1/2 THE LENGTH OF THE ELLIPSE MAJOR AXIS ('A' AXIS)
    B=1/2 THE WIDTH OF THE ELLIPSE (MINOR AXIS)('B' AXIS)
    X,Y=MEAN LOCATION OF CUTS

5) THE INTERPRETATION OF THE ELLIPSE IS YET UNCLEAR TO ME, EXCEPT THAT THE
   RELATIVE SIZE OF THE ELLIPSE IS A MEASURE OF AGREEMENT OF THE DATA.  SMALL
   ELLIPSE GIVES GREATER CONFIDENCE IN THE FIX.

6) TO FIND A FIELD TEAM, ASK THEM FOR TWO BEARINGS TO KNOWN LANDMARKS,
   FIND THE X,Y OF THESE LANDMARKS, ENTER DATA AND COMPUTER PRINTS THEIR
   ESTIMATED X,Y.  THESE BEARINGS MAY BE EITHER OPTICAL OR RADIO BEARINGS.

7) AVERAGING BEARINGS OVER A BASELINE WILL IMPROVE ACCURACY IN MARGINAL
   CONDITIONS.  START BY ENTERING ALL THE X AND Y LOCATIONS TO BE AVERAGED
   AND THE BEARINGS FROM THOSE LOCATIONS.  IF ALL THE BEARINGS ARE TAKEN FROM
   THE SAME GENERAL LOCATION, THEN ENTER THAT LOCATION FOR EACH BEARING.
   AFTER YOU HAVE ENTERED ALL THE LOCATIONS/BEARINGS ENTERING A '51,0,0'
   WILL CAUSE OF THIS THE PROGRAM TO BEGIN CALCULATIONS.  WE ENCOURAGE THE USE
   OF THIS TECHNIQUE EITHER OVER SMALL DISTANCES (EG 300 FEET)OR LONG DISTANCES
   (MILES) WHEN THE DATA DICTATES ITS USE.

8) UP TO THIRTY BEARINGS/LOCATIONS MAY BE ENTERED IN THIS PROGRAM.  MEMORY
   REQUIREMENTS MAY BE REDUCED BY DECREASING THIS NUMBER (CHANGE THE DIMENSION
   STATEMENTS) AND BY INTEGER ARITHMETIC.
                    - CHRIS