JCSM Shareware Collection 1996 September/JCSM Shareware Collection (JCS Distribution) (September 1996).ISO/bother__/sly253a.zip/siy3.txt

Text File | 1995-03-03 | 15KB | 352 lines

SIY3.TXT       Field Survey and Write a Land Description       25


                            Chapter 3


            Field Survey and Write a Land Description


In this chapter you will write a land description just like you
did in Chapter 2.  The only exception is that you will do it from
a map on a grand scale.  The real Earth.

For this chapter you will need:

a) Silva Ranger type 15 compass, available for $43 + $5
shipping & handling from CAVE Inc, 1/2 Fast Road, Ritner, KY
42639.  606/376-3137.  This time there is no substitute for the
real thing.

b) A place outdoors to practice,

c) Pencil and note paper.

You will not need:

a) Tape measure, but when you do need one, an unbreakable 200
foot Keson PVC coated fiberglass surveyor's tape measure is
available from CAVE Inc for $28 + $5 shipping & handling.

b) Clinometer,

c) Assistant,

d) Deed.

e) You don't even need this computer, except to make a printout
so that these instructions can be doodled with a pencil.

You will be doing something different with the compass.  You will
use it for a compass.  Put the compass on like a necklace with a
pendant.  The latest fad.

Open the compass lid.  Tilt the mirror up about halfway towards
straight up.  Hold the compass out in front of you, at about
mouth level.  Close one eye and sight your target thru the vee
sighting notch atop the mirror.  Now look into the mirror,
without moving the compass.  Twiddle with the mirror until you
can see all of the compass dial in the mirror.

 SIY3.TXT       Field Survey and Write a Land Description     26


Don't try to look at the compass dial directly.  You can't see
the dial and still hold the compass level, so don't bother
trying.  The compass must be level when taking a compass
direction.  The compass needle must be free to swing and jiggle
without binding on the compass case.

There is a line in the mirror.  Turn the compass until this line
goes thru the pivot point of the compass needle.  Now turn the
dial until the red and black arrow lines up with the compass
needle.  The needle red and the arrow head.  The old Ranger has
an all black arrow, but don't let that confuse you.  Note that
the needle may not be exactly in the center of the red and black
arrow.  That's OK, just so long as the needle and the sides of
the arrow are parallel.

Your compass direction is under the index blob.  And it will stay
there until you change it.  Read the compass direction at your
leisure.

To take a good compass reading, the following four things must
all happen at the same time.  In what order you do them makes no
difference, as long as they all finally happen at the same time.

a) You see your target thru the vee sighting notch.

b) You see the line in the mirror pass thru the center of the
needle pivot.

c) You see the red and black arrow and the compass needle align.
Needle red, arrow head.

d) The compass needle really is pointing North.

Now that you know how to take a compass reading, find yourself a
place to work outdoors.  A yard or park is the best choice.  It
needs to be level and at least 25 paces square.  A pace is how
far you get in one step.  About 2.5 to 3.0 feet.  Try to find a
place without too much traffic or interruptions.

Pick an obvious place to start.  Try to keep away from steel.
Steel perturbs the compass.  Stay 5 paces away from cars, steel
reinforced pavement, or wire fences.  I don't know how far from a
steel reinforced building is dangerous, never having had that
problem.  50 paces??

Label your paper with headings: TO FROM COMPASS TAPE COMMENTS

 SIY3.TXT       Field Survey and Write a Land Description     27


Your starting point is station 0.  Describe or mark it so that
you can find it again.  You'll know if you have done a good job
of marking it when you try to find it again.  Enter the data for
this station in your notes.  A row of 0 0 0 0.  Remember, you
gotta start somewhere.

Pick your next station.  It is the second station, but name it
"1".  This one need not be permanent.  A wad of paper, a beer
can, or an assistant will do.  Just so long as it stays put for a
few minutes & you can see it from station 0.

Go back to station 0.  Measure the COMPASS direction TO station 1
FROM station 0.  Sight thru the vee sight, put the line in the
mirror in the center of the pivot, and turn the arrow until it
aligns with the compass needle.

The arrow head and the needle red.  Check that the compass isn't
tilted so that it binds the needle.

Now pace off the distance to station l from station 0.  Enter
this information in your notes.

I hope that you don't feel that I have cheated you, but that's
about all there basically is to land surveying.  If you are
really dissatisfied, I'll refund your money.  What can I say?  I
told you that this was ridiculously easy.

For the rest of you, there are a lot of helpful hints.

Organize your data notes the same way as you did in Chapter 2.

TO       FROM      COMPASS      backsight      TAPE      COMMENTS

Record your data for each station.  Be sure that you have
recorded the data for each line before you move on to the next
station.  And always be sure to start somewhere.

You can check your compass technique by taking a compass
direction to station 0 from station 1.  If you align the tail of
the arrow with the red end of the compass needle, you can read
your original compass direction under the index blob.  No need to
fool around adding 180 degrees.





 SIY3.TXT       Field Survey and Write a Land Description     28


This is a backsight.  You took the compass direction to station 0
from station 1.  What you really wanted was the direction to
station 1 from station 0.  These directions are 180 degrees
apart.  You were heading in exactly opposite directions.  Be
careful that you don't make the classic blunder of getting them
mixed up.  Everybody has to do it at least once.  Record
backsights in the backsight column.

Notice that when you are standing on station 1 looking at station
2, your compass reading is TO 2.  When you look back to station
0, your backsight is TO 1.  They are not entered on the same
line.

With a little practice you should be able to get your sights and
backsights to agree within a degree.  For now, five degrees
difference is plenty good enuf.  You might not be able to agree
even within five degrees if you are near a lot of steel.  If you
have this problem, then try a different yard or park before
yelling for help.

The distance is measured in paces.  Just walk between the
stations and count your steps.  Measure to half paces.  If you
want to know the distance in feet, you will have to measure the
length of your pace in feet for a conversion factor.

Your pace should be about 2.5 to 3.0 feet.  By the definition of
a mile (a thousand double paces) it is 2.64 feet [5280 / 2000,
where the symbol "/" is computerese for the arithmetic operation
of divide].  You could use your tape measure if it won't cause a
traffic jam.

You should now have two stations recorded.  Station 0, your
starting station, and station 1, with compass and tape data.
Pick station 2, put something there so that you can see it from
station 1, and go to it.

Put in station 3.

Now put station 4 in the same place as station 0.  Make a note in
your comments that station 4 is the same place as station 0.

Your now have four stations in a loop.  The closure error on the
ground in reality is 0.0 Stations 0 and 4 are in exactly the same
place.

Pick up your trash and go back to your kitchen table, or whatever
you are using for an office.
 SIY3.TXT       Field Survey and Write a Land Description     29


Get out a fresh sheet of note paper.  Transcribe your field
notes.  Make a nice clean office copy without all the doodles and
crossed out mistakes.  (You've already found out that erasures of
bad data are an invitation to blunder.  Cross out those
mistakes.) Be sure to label both the field and office copies with
what you have surveyed, when, with what instruments, and by whom.

Now plot a map from your data.  Just like you did in Chapter 1.
Be sure that you label your map.  Be sure that the North arrow
points up.  A Suggested scale is 10 paces per inch.  Write on
your map: "10 paces = 1 inch" (or whatever scale you are using).
This is so that you will remember the map scale tomorrow.

You should have a closure error of a few paces.  If you wish to
get more technical, you should not have more closure error than 2
paces plus 5% of the run.  If you do have more error than this,
it is not error.  It is blunder.  Go survey it again and find out
what you did wrong so that you don't make the same mistake again.

If you do make the same mistake again, try a different place.
The most likely problem in a city is too much steel perturbing
the compass.  How well do your sights and backsights agree?

Now find a place where you can try the 200 foot surveyor's tape
measure.  Note that the tape measure is graduated in feet and
tenths, not inches.  This makes the calculations a lot easier.

I like to call TAPE by the name PACE when I'm doing a pace
survey.  That makes it easier to understand my notes later.

If you can't find a convenient place to use the tape measure,
just continue.  Play with the tape when you find a safe place.

If you wish, you can plot your map at the same time as when you
collect your survey data.  Your protractor is already set to the
proper direction.  The ruler is right there in your hand too.
This is the great advantage of the Silva Ranger over other
systems.  Replot your field map when you get back to your kitchen
office.  Plotting as you survey helps you to keep track of what
you are doing, and catches blunders.

This can be especially important when surveying where you can't
see what you are doing, such as in a deep dark dank crawly twisty
hole in the ground.



 SIY3.TXT       Field Survey and Write a Land Description     30


All this time you have assumed that the compass needle was
pointing North.  It wasn't, but it was close.  The compass
doesn't point towards The North Pole, but rather to The North
Magnetic Pole.  Adjust the declination on your compass.  Turn the
declination adjusting screw located at 45 degrees on your dial.
Use the screw driver on the safety cord.  Read the declination
under the tail or head of the black arrow.

It doesn't make any difference which end of the arrow you use,
but you might understand better which way is which if you use the
arrow head as the declination pointer.  Even Silva gets confused
when they try to set declination on the south!

The Silva instructions have a map of the United States of America
with the declinations marked.  Or look on a topographic map.  Or
ask your local Geological Survey.  Note that if you move a
hundred miles or so east-west, you must readjust the
declination.  Declination also changes with time.  I usually set
the declination to 0.0 and correct the compass with my computer
program.  If I bother to correct it at all.  The declination read
from the Silva instructions will be plenty good enuf for you.

If you have a modem, then you can call the USGS Branch of Global
Seismology and Geomagnetism.  This is a US Government computer,
so it has some odd parameters.  Set your modem for 300 or 1200,
7, S, 1.  The toll-free number is 800-358-2663.  When you finally
get to the main menu, select M for Geomagnetic Field Values
(GEOMAG).  There is a helpfile available.  You will need to know
the latitude, longitude, elevation, and date for which you wish
to know the magnetic declination.

Steel objects perturb the compass.  I can't say it often enuf!
Cars, fences, axes, guns, knives, motors, buildings, steel
reinforced pavement, and maybe even your eyeglass frames,
jewelry, wristwatch, or pacemaker will affect the compass.  When
in doubt, test.  See how close to the compass needle the object
must be before the needle is affected.  Then at least triple it
for safety.  For a movable object, have an assistant move it
around while you watch the compass needle.  For an immovable
object, sight on a distant target, then move along the line of
sight away from the test object and take another compass
reading.  If you were far enuf away, the compass reading will not
change.




 SIY3.TXT       Field Survey and Write a Land Description     31


Some places have magnetic rocks which disturb the Earth's
magnetic field which your compass is sensing.  If this is the
case, then you are out of luck.  Such places are usually in areas
of mining activity or of metamorphic rock.  You can't survey with
a compass in Lodestone Gulch nor on Magnetic Mountain.

Silva claims that their sealed liquid filled compass capsule
resists static electricity interference.  I never heard of static
electricity affecting a compass, but the magnetic field created
by direct current sure does.  There is no resistance possible
either, since it is the magnetic field which is perturbed.  The
compass aligns with the perturbed field just like it is supposed
to do.

Sloppy technique is another problem.  The Ranger is much more
accurate when used on the lanyard than when held freehand.  Be
sure that the compass is pulled to the end of the necklace.  This
both steadies it and keeps it in the proper position.  If the
target is almost in the vee sighting notch, or if the mirror line
is almost in the center of the needle pivot, or if the arrow and
the compass needle are almost aligned, then you will get almost
the correct compass direction.

The worst problem with the Silva Ranger compass is not keeping
the compass level.  You can have an assistant check this for you,
or you can check it yourself.  Tap the side of the mirror with
your finger.  The needle should jiggle and return to the same
place.  If the needle is not free to jiggle, then the compass is
tilted and you will get the wrong compass direction.

Another trick is to flop the compass over on its side, then sight
it again.  The needle and the arrow should line up again.
Perfectly.

You should try surveying in the park a few times so that you make
most of the normal beginner's blunders in a safe place.

Copyright (c)1995 by David Perry Beiter

If you have any questions, problems, or comments, write or call
me.
Dave Beiter, CAVE Inc, 1/2 Fast Road, Ritner KY 42639.
606/376-3137.
MCI Mail: 635-1762
[e-mail]
X.400: c=US;a=MCI;s=BEITER;d=id=6351762
CIS: >MCIMAIL 635-1762 (be sure to include your name in the text)