Cream of the Crop 3/Cream of the Crop 3.iso/comm/aprs403x.zip/README.CD

Text File | 1994-02-14 | 7KB | 111 lines

README.CD

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 12K APRS MAP!  IT TAKES ME AT LEAST 4 HOURS PER MAP!  I
PLAN ON EVENTUALLY DOING THE TOP 20 CITIES.  IF YOU WANT A SPECIAL ONE OF YOUR
AREA, SEND $80.  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!  Next MAPFIX allows you to
    round the ORIGIN values, to reasonable nearly whole numbers.  Using
    good round numbers here, makes it easy to use a paper map in the future to
    derive additional manual points.

3.  Use the alt-U command to select the S0x_RD.GRF file for the roads.  MAPFIX
    will then scan the entire ROADS 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.  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.

5.  Now you have the smallest APRS map that can be done automatically.  Move
    the MAP POINTER to the beginning FEATURE using the PREVIOUS 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 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, but will probably
    eliminate 200 or more points!

8.  Notice that you only have roads so far.  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.

9.  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 command
    and ADD commands to draw APRS features using the overlay as a guide.  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 and ADD 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.  NEVER do a second
    USGS BUILD, because it will clear memory and start from scratch.

LOOK AT MY GAtlanta, FLTampaO, TXDallas and TXHoustn maps done in this manner...