TPC Technote
Carrying Elevations
There are three main ways to carry elevations in
TRAVERSE PC. The first is through the use of bench marks and turning points.
The second is by measuring the height of the instrument. The third is by
translating groups of points up or down so that side shots taken to points
of known elevation are at the correct elevation.
In the discussion that follows,
BM is the notation TRAVERSE PC gives to a point which
is sighted to establish the elevation of the instrument's optics.
Bench Mark is a permanent point of known elevation.
Turning Point is a temporary point of known elevation,
typically established to carry elevations forward in a traverse or level
loop.
Bench Marks and Turning Points
A typical traverse view using bench marks might
look like this,
(ref az)
C1
(slope dist and zenith with HT)
BM BM1
(side shot data with HT = Height of Target)
SS 1
(side shot data with HT)
SS 2
(side shot data with HT to establish the elev. of
next bench mark)
SS TP1
(data to next occupied point with or without HT)
C2
(slope dist and zenith with HT)
BM TP1
(side shot data with HT)
SS 3
BM1 is some bench mark (point of known elevation).
The user would enter its elevation and some observed data used to establish
the elevation of the instrument optics based on the elevation of the bench
mark. To treat BM1 as a bench mark, highlight it and choose Type | BM=Bench Mark.
The first turning point, TP1, is entered as a side
shot from C1 to establish its elevation. Since it is a side shot, coordinates
are also established, even though they may be incidental. TP1, is then
referenced as a BM and used to establish the elevation of the instrument's
optics at C2.
The BM observation must immediately follow the occupied
point in the Traverse View.
This is essentially the same as differential leveling
with foresight and backsight rod readings except that trig levels are used
instead. Elevations need not be computed for occupied points but will be
automatically computed for each foresight for which a target height is
recorded.
The height of the target, if used, is added and subtracted
from both side shot and bench mark observations to correctly establish
the elevations of the points.
Measuring Instrument Height
The second method of carrying elevations is to measure
instrument heights. A typical traverse view might look like this,
(ref az)
C1 (enter HI and known or assumed elev. of C1)
(side shot data with HT = Height of Target)
SS 1
(side shot data with HT)
SS 2
(data to next occupied point with HT)
C2 (enter HI)
(side shot data with HT)
SS 3
This seems to be the preferred method with Wild instruments
and others that measure HI's through the optical plummet.
This method differs from the first in that it establishes
elevations for each occupied point. With the bench mark method, establishing
the elevations of the occupied points is optional.
Translating Points
This method involves sighting a point of known elevation
(either a bench mark or a turning point) from each occupied point, then
translating all of the side shots and foresights taken from an occupied
point so that the elevation of the side shot to the bench mark or turning
point matches the known elevation of that point. A typical traverse view might look like this.
C1
(slope dist and zenith with HT)
SS BM1:1
(side shot data with HT = Height of Target)
SS 1
(side shot data with HT)
SS 2
(side shot data with HT to establish the elev. of
next bench mark)
SS TP1
(data to next occupied point with or without HT)
C2
(slope dist and zenith with HT)
SS TP1:1
(side shot data with HT)
SS 3
The points BM1:1, 1, 2 & TP1 would all be translated
so that the computed elevation of BM1:1 matched the known elevation of
BM1. In the process of translating these points, TP1 would be established
at the correct elevation.
The points TP1:1 & 3 would then be translated
so that the computed elevation of TP1:1 matched the translated (correct)
elevation of TP1.
The easiest way to translate a group of points is
to highlight them and copy them to the scrap traverse. Then translate the
scrap traverse.
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