Shareware Overload Trio 2/Shareware Overload Trio Volume 2 (Chestnut CD-ROM).ISO/dir24/aprs60.zip/CDROM.TXT

Text File | 1994-09-28 | 10KB | 153 lines

CDROM.txt 6.0          HOW TO BUILD APRS MAPS FROM THE USGS CD ROM


JUST BECAUSE I CAN NOW MAKE MAPS FROM THE USGS 2,000,000 SCALE CD ROM, DO NOT
GIVE UP DRAWING MAPS BY HAND.  THE 2,000,000 SCALE CD IS ONLY GOOD FOR 64 MILE
MAPS AND THEY DONT EVEN HAVE AS MUCH DETAIL AS A STATE HIGHWAY MAP.  ALSO
IT STILL TAKES A LOT OF MANUAL EFFORT TO REDUCE THE INITIAL 5 MBYTES OF
USGS DATA DOWN TO A 15K APRS MAP!  IT TAKES ME AT MORE THAN 4 HOURS PER MAP!
I PLAN ON EVENTUALLY DOING THE TOP 20 CITIES.  IF YOU WANT A SPECIAL ONE OF
YOUR AREA, SEND $$$ or convince me it is in the general best interest of
all HAMS.  THAT ALONE SHOULD KEEP YOU INTERESTED IN DOING YOUR OWN.  HI HI

There are three problems with the USGS data base that causes excessive points
in an APRS map.  First, line segments begin and end at EACH intersection.  For
am interstate, for example, you end up with dozens of short road segments
wasting 3 point pairs per exit.  Second, these short segments are not always
consecutive in the file, making it extremely time consuming to try to join
them.  Third, the USGS data guarantees a point every 1/3 mile whether it is
needed or not.  A 10 mile long straight road is stored as 30 points in USGS
vice 2 points in APRS.  Here is a sumary of the process used to get it down
to size:

1.  Use USGS XTRACT.EXE program to extract the CD ROM data in the GRAPHIC
    format for your area from one of the dozen or so major USGS areas.  Then
    select up to 6 files for extraction onto your HARD disk, one for each of
    the data types, BOUNDARIES, ROADS, WATER BODIES, STREAMS, RAILROADS, and
    HYPSOGRAPHY (continental divide).  These files will take about 5 MBytes.
    To save HD space, and also to end up with the minimum of points, you will
    probably only use the ROADS, WATERBODIES, and STREAMS files.  Note the
    filename assigned by XTRACT.

2.  Run MAPFIX.BAS program and load the best existing APRS map that covers
    the desired area.  This map is only used to help you locate the area of
    interest.  Next, move the cursor to the center of interest and select
    a SCALE using the BOUNDARY (B) command.  This command will show you the
    maximum map possible for a given scale in Points/per degree.  I have found
    600 to be about right.  450 in sparse states and 300 in UTAH and NEW Mex.
    If you use any less, to get larger maps, you will end up with far too many
    points.  I used 450 for the SouthCarolina map, and it took me 6 hours to
    get the resulting 3000 points down below 1500!  In the East, I used 900
    for a 35 mile map around Philidelphia.  Making maps any smaller is probably
    not worth the effort, since there will be so few roads in it..

3.  When you have the B command set to the desired number of Pixels-per-degree,
    press the alt-U key.  MAPFIX will allow you to round the ORIGIN values, to
    reasonable nearly whole numbers or fractions of a degree so that later
    manual operations with a map and ruler will have round numbers to deal
    with.

4.  Next APRS asks you for the exact path to the XTRACTed USGS data.  This path
    should include the filename up to the first (_) underline separator.  THen
    MAPFIX asks for the type of file, such as RD, ST, WB, etc.  MAPFIX
    will then scan the entire indicated file for all points within the selected
    border.  While converting the points to APRS format, MAPFIX will also
    compare the slope of each new point with the previous point and ignore
    the point if it has approximately the same slope (within 1.5)  The total
    number of points will be from 2000 to 4000.

4.  Next MAPFIX has a SMOOTHER command which will run another slope comparison
    process.  You can select the SMOOTHER factor.  A factor of 1 will only
    throw out points that are exactly the same slope (few if any).  A factor of
    1.5 (best) will throw out points whose slope differs by less than 1.5.
    Bigger values will throw out  more points (usually including some necessary
    ones).  To test the smoothing algorithm, run the TEST SMOOTHER command which
    will mark every point that would be eliminated with a red dot, and every
    point that will be kept with a yellow dot; but without actually eliminating
    any points.  Look at the map closely and see if you can accept the decisions
    of the SMOOTHER.  Select your chosen factor and run SMOOTHER. (alt-S)

5.  Now you have the smallest APRS map that can be done automatically.  Move
    the MAP POINTER to the beginning FEATURE using the RESET command and
    use the gray +/- keys to cycle through EVERY point in the file.  Use the
    alt-D key to delete all unnecessary points.  Look for complete duplicates
    of some lines too.  This should get you down to below 2000 or so.

6.  Save the file.  Load it into a text editor and start at the beginning of
    the file.  Look at the beginning and end of every line segment.  If the
    points are the same, eliminate the 0,0; color,LineName; and the duplicate
    point.  Be sure to check the color, and only concatonate roads of the
    same type.  (MAPFIX will now do this step automatically with the JOIN
    command).

7.  Next, use MAPFIX to do step 5 again.  Look at intersections where you have
    joined two line segments.  If the road goes straight through the
    intersection, then the intersection point can be deleted.

8.  If you still have too many points, go through the TEXT editor again and
    use the SEARCH feature to search the file for the beginning and end points
    of every line.  Each time you find a match, move the points around and
    concatonate the line segments.  This is laborous, and only eliminates
    one point per process, but can be useful in congested areas, where many
    nearby line segments only have two or three lines anyway.


9.  Notice that you only have one category of features so far (usually roads).
    Unless you require county lines I recommend that you ignore them.  The
    USGS BOUNDARIES file contains even more points than the ROADS file!  AND
    the SMOOTHER routine does not work well, because property lines are very
    jagged, unlike smooth curves in roads.  The same thing goes for WATER
    BODIES and STREAMS.

10. To allow you to add some detail from these other USGS files, MAPFIX has
    the USGS OVERLAY feature which will overlay the USGS data on the APRS map
    without doing anything.  Then you can use the MAPFIX NEW-FEATURE and ADD
    commands to draw APRS features over the top of these temporary points.
    The philosopy here is that 96% of amateur interest is on roads, and you
    can sure burn up points on waterways and county lines.  For rivers, about
    the only points I use are where the water goes under a bridge.  Most folks
    have no idea where a river is out in the boonies (and could care less).
    Of course, if you are making a map for boats with GPS, then start the
    process with the WATERBODIES file and add just enough roads for them to
    find the boat ramps..
       You will first need to overlay on the 64 mile scale to see where things
    are, but then zoom into the 8 mile scale at least and do the overlay again
    to get enough resolution for drawing a particular feature.  You can use the
    NEW, ADD and MOVE commands, but any other commands will redraw the map and
    wipe-out the overlay.  I have added the Ctrl-R command to toggle the map
    REDRAW process on and off.  This may help you to add lines without destroying
    the USGS overlay.  You can do the overlay again and again.

WARNING!:  NEVER do a second ALT-U USGS BUILD, because it will clear memory
    and start from scratch.


CAUTION:  Do not expect too much from this CD ROM.  ALthough the 2,000,000:1
    USGS database seems to have resolution down to 1/3 rd of a mile, remember
    that that 1/3rd of a mile was actually 1/100th of an inch on the original
    map!  Your 64 mile section was only a two inch square!!!!!  AND THE DATA
    WAS PROBABLY DERIVED BY A HIGH SCHOOL SUMMER STUDENT using a mouse!

      I have found this data to be very crude, and although the maps lines
    look smooth, you are getting about the same quality as if you were
    looking at a state highway map through a magnifying glass!  If you want
    good detail, use MAPFIX and a digitizer on a much better original map,
    such as a 100,000:1 or even 24,000:1 (which is the standard USGS 7.5
    minute map).  There you can get down to your driveway!


FUTURE MAPFIX with USGS 100,000:1 DETAIL CD ROMS

    FORGET IT!  W7KKE has made an attempt at it, and just a few square mile
    area, generates thousands of points.  The disjointedness of the resulting
    line segments are even worse than the 2,000,000 data, and he says it takes
    days to generate just each type of feature!  Then you have to combine these
    features.  There is no way this will EVER be competitive with the 2 hours
    or so that it takes to digitize excellent data from a paper copy of a
    100,000 or 24,000 map.  The problem is, that getting the paper maps by
    mail, takes weeks.  If you need a special map, send me the paper and from
    $80 to $150 per map!  Dont forget, that you can still do it yourself with
    a pencil and ruler in only about double that amount of time, and once
    you have done it, you can modify your map at any time!