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John Adolphus Flemer.

An elementary treatise on phototopographic methods and instruments, including a concise review of executed phototopographic surveys and of publicatins on this subject online

. (page 22 of 33)
Online LibraryJohn Adolphus FlemerAn elementary treatise on phototopographic methods and instruments, including a concise review of executed phototopographic surveys and of publicatins on this subject → online text (page 22 of 33)
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rectly placed, we may proceed as follows:

A theodolite, Fig. 163, Plate LXXXVI, is set up about 10
or 15 metres behind the cylindrograph (after the back of the
camera had been removed to bring the indices H and H' into
view) and both instruments are leveled. After bisecting the
upper edge of the cylindrograph and the telescope of the theo-
dolite is moved in azimuth the bisection should continue, and
the same should be the case for the lower surface edge of the
cylindrograph. If this does not take place, then the cylindrograph
should be adjusted by means of the leveling-screws until the
bisection does take place and the level A is then changed to
read zero. The theodolite is now set up in the direction of the
level A (at one side of the cylindrograph) and the level B is
adjusted in a similar manner as just described for A.

To adjust the indices H and H' into the horizontal plane'
containing the optical axis of the adjusted cylindrograph a com-
parison may be made on a cylindrograph picture showing several
points of known elevations, the elevation of the cylindrograph
being also known, or the theodolite may be set up with the hori-
zontal telescope at the same elevation as the optical axis of the
adjusted cylindrograph. The horizontal telescope of the theo-
dolite is now moved in azimuth until a well-defined point is



274 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

bisected, which point may be identified on the ground glass of
the cylindrograph. The image of this point on the ground
glass is marked and the cylindrograph is moved in azimuth,
marking the image on the ground glass in two more places. A
(horizontal) line passing through these marked points should
pass through H and H f .

The objective is attached to a funnel-shaped box situated
within the camera (see Fig. 160, Plate LXXXII) and permitting
the simultaneous exposure of a vertical strip of film of a width
of but 62 mm. Points of the film that would be pictured out-
side of this strip cannot be acted upon by the light-rays until
the objective be revolved (about the axis aa) sufficiently far
to expose them to the effects of the light. After the time needed
for the correct exposure of this strip (of 62 mm. width) has
been ascertained (by experiment or otherwise) the correct expos-
ure may be given the entire semi-cylinder by moving the sight-
ruler S, with a quick uniform motion, about aa, from one extreme
end of the film to the other. The semi- cylindrical film being
860 mm. long, each strip of the film would then have been exposed
the 62 /86oth part of the time required to make one full revo-
lution of the objective. If one complete revolution required
10 seconds, and if the correct exposure for the strip was found
to be 5 seconds, each strip would have received an exposure of

- seconds = 0.72 second. To give each strip the required
exposure of 5 seconds the entire revolution of the lens should

be repeated times, or about seven times, each revolution
0.72

taking 10 seconds.

These panorama instruments are not made sufficiently .pre-
cise, in their present form at least, to be recommended for topo-
graphic surveys. Moessard's cylindrograph, however, is well
conceived, and where the transportation is an easy one, the
topographic cylindrograph, in a more perfected form, may give
results sufficiently accurate for surveying purposes.



CHAPTER X.
ICONOMETERS AND PERSPECTOGRAPHS.

UNDER iconometers we comprise a series of instruments
which have been devised to simplify the constructions of photo-
topographic plotting or iconometry.

After two drawing-boards have been covered with paper
(gummed down on the edges), both sheets are provided with a
chart projection upon which all trigonometric (triangulation)
points are plotted and their elevations inscribed.

The construction incidental to the iconometric plotting of

the phototopographic survey may be divided into three classes:

First. The plotting of all horizontal directions that had

been observed, instrumen tally, for the location of the

camera stations and for the orientation of the panorama

views.

Second. The determination of the horizontal projection of
points pictured on three or more photographs, taken
from different stations.

Third. The determination of the elevations of the various
camera stations and tertiary points that are located icono-
metrically ta facilitate the plotting of the horizontal con-
tours of the terrene.

I. Graphic Protractor (of L. P. Paganini).

With the aid of a specially constructed protractor, Fig. 164,
Plate LXXXVII, and tracing-paper the directions obtained
with the theodolite or transit in the field can readily be plotted

275



276 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

upon both the working- and chart-sheets. This protractor,
represented in Fig. 164, Plate LXXXVII, consists of two con-
centric rings A A and BB, the former being movable within the
latter about the common axis C, secured in the center of A A
by means of the plate aa. The rotary motion is applied to A A
by means of two projecting ribs as and sa on the plate aa.

The inner circle AA has a graduation divided into degrees
and half degrees, while the outer circle BB bears a vernier n,
reading to half minutes, the zero of which lies in the prolongation
of the fiducial edge of an arm bb, the latter being permanently
secured to the outer circle BB and in a radial position to the
same. The clamp-screw P serves to hold the two circles in
any position.

An alidade ruler, DD, the fiducial edge of which also passes
through the center C, common to both circles, is revolvable about
the axis C and it may be moved over the upper surfaces of the
two circles A A and BB. This ruler, DD, bears a vernier n',
graduated like n to read to half -minutes and its zero coinciding
with the fiducial edge of DD. The clamp-screw P r serves to
clamp this movable arm DD to the outer circle BB.

The axis C has a conically shaped hollow interior, at the
bottom of which a thin piece of isinglass or horn is secured in
such a manner that it may be removed for renewal whenever
the small puncture indicating the center of the circles and axis-
of revolution be worn too large.

When using an ordinary protractor to lay of! the various
directions (radials, that were observed with the transit in the field)
from one camera station, much valuable time will be absorbed
in making the additions and subtractions (which have to be
made in order to obtain the actual values for the successive angles
between such lines of direction), particularly when a series of
panorama stations are to be plotted.

The protractor, as shown in Fig. 164, Plate LXXXVII, may
be used not only as an ordinary protractor by bringing the
zeros of both circles to coincide and clamping the two circles



L. P. PAGANINl'S GRAPHIC PROTRACTOR. 277

in that position, by means of the clamp-screw P but it may
also be used to plot the directions upon the map or working-
sheet in the same manner as they were obtained in the field with
the transit; that is to say, they may be referred to zero or to
any other direction as the beginning, and then be plotted in
successive order.

To do this, the inner circle is revolved until the zero of BB
(vernier ri) gives the same reading upon the graduation of the
movable circle A A as the recorded reading on the transit for the
prime direction. Now both circles are clamped together by
means of the clamp-screw P. The line of prime direction is
drawn along the fiducial edge of the fixed ruler bb upon the work-
ing-sheet (or upon tracing-paper if the station is to be located
or fixed upon the tracing of the lines), the center C of the instru-
ment coinciding with the point representing the station upon
the paper.

The zero of the vernier ri of the alidade DD is then brought
successively (upon the inner- circle graduation) to the readings
of the other directions which radiate from the plotted station
point at C, each direction being plotted in successive order by
drawing a pencil line along the edge of the alidade DD. Care
must be exercised not to change the primary position of the
instrument as defined by the first line during all subsequent
motions of the alidade ruler DD.

With the aid of this instrument the radials from the plotted
camera stations may be obtained with rapidity and accuracy.
If we have a sufficient number of directions to well-determined
points which are evenly distributed about the station, their
corresponding intersections upon both drawing-boards may be
plotted with as much rapidity and accuracy as a graphical plotting
will admit of.

This protractor may also serve to locate points on the con-
struction board that, on account of importance or for reasons
of control, had been bisected from several stations with the
transit, and also, as will be shown, to orient a perspective view



278 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

(the picture trace) upon the board, if such perspective contains
no triangulation point, or when the picture of such point is blurred
or not sufficiently well denned to be identified with precision..

After all stations, including such secondary and tertiary
points that were determined by transit observations from the
several camera stations, have been plotted upon the two boards,
the work of iconometrically determining, upon the working-
sheet, such points as seem needed to complete the map is taken
up. For this purpose the various elements of the perspectives
are tested and corrected, if needed, after the manner previously
described, and all tertiary points are selected, identified, and
marked, searching for well-defined points common to two or
more plates, carefully selecting therefrom only such as appear
to be the most useful, either for drawing the contours or for
tracing the general trends of mountain ranges, torrents, and
streams, boundary lines of glaciers, etc., the number to be
selected depending greatly upon the character of the terrene,
upon the adopted scale, and upon the accuracy to be attained.
All tertiary points are marked upon the prints (perspectives)
by numerals, letters, or symbols in red ink.



II. L. P. Paganini's Graphic Sector (" Settore Grafico ").

Instead of actually drawing the horizontal projections of all
perspectives (the picture traces) upon the working-sheet, much
time may be saved by using the instrument represented in Fig. 1 66,
Plate LXXXVIII, devised by Paganini, who termed it " settore
grafico," or graphic sector. With this graphic sector the hori-
zontal directions to points marked upon the prints may be drawn
cirectly on the horizontal plan without first drawing the picture
traces.

In Fig. 165, Plate LXXXVII,

V represents the station, plotted on the working- sheet;
OO' the horizontal projection of a perspective (the picture



L. P. PAGANINI'S GRAPHIC SECTOR. 279

trace, oriented with reference to the plotted triangulation
point 5) ;

/ = focal length for the perspective OO' ;
P = principal point (of view) of the perspective;
Ps upon OO' is the measure of orientation of the perspective,

corresponding to the azimuthal angle w;
VP is perpendicular to OO' and =/.

We now prolong VP beyond F by FP=FP'=/ and erect a
perpendicular to FP' = O'"O" in P'. Produce, likewise, VB,
VA, VS to their intersections with O'"O", which intersections
are marked V, a! ', and s', respectively.

FP' = FP
and 00' parallel to O'"O";

hence the rectangular triangles VP'af, VP'V, and FPV are
congruent with FPa, FP6, and VPs respectively. Therefore



and

giving also the measure of orientation ( = aj) of the perspective
of the picture to the picture trace.

The screw e serves to clamp the screw m whenever the posi-
tion of T with reference to F is to be fixed, after it has been
brought to the desired distance from the center of rotation F.
Two thumb-screws W and W f (with hollow centers into which
fine needles may be inserted to hold the sector in place after
having been adjusted over a plotted station) serve to secure the
metal sector in any desired position upon the drawing-board.

The arc SS f of the sector is graduated to ten minutes, and
the zero of this graduation coincides with the axis FP of the
instrument, giving readings from o to 25 to either side of FP.

The ruler or alidade RR' is provided with a vernier F, by



280 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

means of which the arc readings may be obtained within 30
seconds. The thumb- or clamp-screw Z of the alidade has a
counter plate at its lower end to secure the end R f of the alidade
ruler upon the arc ss' of the sector and upon the steel ruler T.

In order to draw the lines of direction upon the construction
board to a point of the terrene (the picture of which had been
identified and marked upon the perspective) the instrument is
placed with its center of rotation, F, over the needle, marking
the camera station on the working-sheet, and the button r is
given a quarter-turn (care must be taken that the side bearings
of the button r of the instrument may have no loose play about
the needle), then T is moved by turning the screw m until OO'
is distant from the center F by VP = j, whereupon the orientation
of the instrument is accomplished as follows:

RR' is to be directed to bisect a plotted triangulation point
the image of which appears on the perspective sufficiently dis-
tinct to serve as a reference point; its abscissa is taken from
the photograph by means of a pair of dividers and plotted, in
the inverse direction, upon the line OO' from the puncture,
marking P; the alidade ruler RR' is now gently brought into
contact with the other point of the dividers and it is secured in
this position by clamping Z.

Now the entire instrument is revolved about F until the
end R of the alidade bisects the plotted triangulation point, when
VP will indicate the direction of the principal line and OO' will
be parallel to the picture trace, which really would fall beyond F
at a distance from V=VP = }.

The instrument is secured in this position by gently turning
the screws. The construction of the graphic sector, Fig. 166,
Plate LXXXVIII, is based upon the preceding consideration,
and it serves to draw from the station point F, on the horizontal
plan, the various horizontal directions to points pictured on
the panorama views.

The metal plate VSS', shaped like a sector, may be revolved
on the surface of the working- sheet, about the center of a.



L. P. PAGANINl'S GRAPHIC SECTOR. 281

needle, puncturing the plotted station in the center r of the
sector.

This needle passes through an oblong opening (of the same
width as the diameter of the needle) of a revolvable button at r,
secured in V, and through a similar slot at V in the metal sector
plate VSS'. The metal ruler RR' is revolvable about V, gliding
with the end R' over the arc SS' of the sector plate. The fiducial
edge of the ruler RR' passes through the center of V or r, where
it is secured to the revolvable button r by means of a cylinder,
the bottom of which is provided with a slot similar to those in
the button r and sector plate just mentioned.

When the ruler RE! and the button r are in a certain position
these three slo.ts (in sector plate, button, and ring of ruler) will
coincide, one falling above the other, and the needle may then
be inserted through the three superimposed slots into the sta-
tion point under F, the center of rotation. By a quarter- turn
of the button r the needle will become inclosed in a square, of
which the needle circumference will form the inscribed circle.
The entire instrument may now be revolved about the needle
center in V.

The lever-screw m serves to move the steel ruler T parallel
with itself and vertical to the axis nn' of the screw m. The axis
of the screw m coincides with the direction of the central axis
of the sector which passes through V and the middle of the arc 55'.
When m is turned the ruler T glides up or down, its ends moving
along the grooves u and u> ', the inner edges of u and u' being
graduated, so that the distance of the edge OO' of the ruler T
from V may be read off to o.i mm.

If the edge OO' of the steel ruler T is brought to a distance
VP = f from the camera station in the center of F, by turning
the screw m it will represent the trace of a picture with the focal
length / (in inverse position, however, as it will correspond to
the horizon line as viewed upon the ground-glass plate of the
camera) (see Fig. 165, Plate LXXXVII).

The point P, intersection of the axis of the instrument with



282 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

OO', will represent the principal point, plotted in horizontal
plan. It is marked on the edge of OO' by a small conical cavity
to receive the point of one arm of the dividers when the abscissae
of pictured points are transferred from the horizon line. W and
W are now pressed down, whereby the fine needles in the
centers of W and W are pressed into the working- sheet. The
end R' of the alidade is now released and the abscissae of all
points, identified and marked on the perspective, are transferred
to the line GO' from P, by means of the dividers, in their succes-
sive order but in inverse direction (the fiducial edge of the
alidade RR f being gently brought into contact with the point
of the dividers each time), and the lines of direction are drawn
along the fiducial edge of the ruler end R with a well-pointed
hard pencil.

Should the image of the triangulation point be indistinct
or appear blurred upon the perspective, the instrument will
have to be oriented upon the drawing-board by means of the
angle of orientation ( = o>) of the photograph, which angle had
been observed in the field (in the Italian survey that angle is
recorded in the field book, Model I, Chapter VIII).

The end R f of the alidade is placed and secured in such a
position that the fiducial edge of RRf forms the angle CD with
the axis VP of the instrument, which angle is laid off (in the
inverse direction of the one observed) on the arc SS' of the sector
by means of the vernier v. The instrument is then revolved
about the needle in V the same as before, until the end R of
the ruler passes through the trigonometric point in question
marked on the plotting-sheet. The instrument having been
secured in this position, by turning the screws W and W' t is
used in the same manner as just now described for drawing
the radials which served to locate the pictured points on the plan.

If a plate had been exposed while the vertical thread (prin-
cipal line) bisected a triangulation point, the angle to becomes
zero and the orientation of such photograph trace on the plot-
ting-sheet may be accomplished by bringing the zero of the



L. P. PAGANINl'S GRAPHIC SECTOR. 283

alidade vernier v to coincide with the zero of the arc gradua-
tion, 55', clamping RR f in this position and directing the end R
of the ruler to bisect the plotted triangulation point in question
and securing the sector upon the working-board in this position.

Should, finally, the perspective of which the trace in hori-
zontal plan is to be plotted contain no images of points pre-
viously located and plotted, then the zero of v is again made
to coincide with the zero of the arc 55' and the instrument is
revolved about the center of the needle V until the fiducial edge R
of the alidade coincides with a line that had been drawn from
the plotted station by means of the graphic protractor previously
described, which forms in V (station point) an angle with the
horizontal direction to some triangulation point observed in the
field and equal to the angle of orientation ( = u>) of the plate.
This angle is taken from the field note-book (Model I, Chapter
VI, I-C-6) and laid off on the sector in the inverse direction
and the sector is again oriented in the manner shown before.

After the horizontal directions to the different points, iden-
tified on the panorama pictures, have been drawn with the graphic
sector, they are provided with numerals or symbols to correspond
with the designations affixed to the points upon the panoramic
views, in order to facilitate their identification when seeking
for the subsequent intersections with radials to the same points
from other camera stations. The positions of the secondary
and tertiary points on the plotting-plan are secured by inter-
sections, as has been described in the preceding chapters, and
they serve to make up the control of the map. It is well to
transfer to the final drawing by means of tracings, which are
oriented with reference to the plotted triangulation points and
previously located camera stations, all the different points
obtained by intersections upon the construction board, in order
to erase therefrom all lead-pencil lines which served for their
determination, to obscure as little as- possible subsequent con-
structions fox the location of the positions of other points of the
terrene.



284 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.



III. L. P. Paganini's Graphic Hypsometer (" Squadro grafico ")

After the plotting of the positions of the more important
secondary and tertiary points, in the horizontal sense, is well
under way, it remains to ascertain the elevations of the various
stations, including the secondary and tertiary points of the per-
spectives, in order to enable the draughtsman to interpolate the
contours between the plotted points that control the terrene
forms of the area to be mapped.

The elevations of all plotted camera stations may be ascer-
tained by aid of Paganini's graphic hypsometer, Fig. 167, Plate
LXXXIX, using the plotted distances between the camera sta-
tions and surrounding triangulation points and the correspond-
ing angles of elevation, which had been observed to the latter
from the camera stations and which are recorded in the field
note-books (Model No. I, Chapter VIII).

The elevations of all secondary and tertiary points may be
determined with the same instrument by means of their graph-
ically measured distances from the camera stations and their
corresponding ordinates (y) measured on the perspectives.

Two rulers LI! and MM', Fig. 167, Plate LXXXIX, may
be made to glide with their ends L f and M f along a ruler AB,
always maintaining a position perpendicular to the latter, how-
ever, for which purpose their ends are secured to two sleighs L"
and M" which fit into two parallel grooves g and g'. The
motion of LL f , or rather L n ', is free, and it is accomplished by
pushing the button O up or down the ruler AB.

M" is provided with a ratchet and pinion P. By turning
the latter in one direction or in the other the ruler MM' will
be gradually moved up or down AB, as the latter is provided
with a row of teeth into which the ratchet-wheel of M" bites
while P is being revolved.

The alidade ruler d'd is secured with one end, d, in V in such
a manner that dd' may be freely revolved about the axis of V



L. P. PAGANINI'S GRAPHIC HYPSOMETER. 285

as a center, while the other end, d' ', passes over a graduated
arc Ggg'. The plug in V is similarly constructed as the one in V
of the graphical sector, Fig. 1 66, Plate LXXXVIII (it is pro-
vided with a revolvable button containing a slot, in such a man-
ner that the ruler AB may be revolved simultaneously with
the alidade d'd about a needle, marking the station point on the
construction board). In this instrument the plug, the revolvable
button, and the alidade ruler dd' have each a slot which inter-
sect each other in the center of rotation V, and through which the
needle marking V may be passed when they all have a certain
position, the needle being again secured in place by a quarter-
turn of the button. The entire instrument may be revolved
about the needle in V.. the center of which lies in the directions
of the fiducial edges of the ruler AB and alidade dd'.

The alidade ruler dd' is provided with a vernier , graduated
to read to 30 seconds on the graduation of the arc Ggg' . This
vernier serves to lay off angles from V included between the
fiducial edges of AB and dd'. When dd' is brought close to
and in contact with AB, the zero of the vernier n and the zero
of the arc graduation Ggg' will coincide. The axis of the instru-
ment is represented by that edge of AB (facing dd') which passes
through the center of rotation F, and which passes through
the zero of the graduated arc Ggg'] it also passes through the
point p of the line pq, which is marked upon the ruler MM'j and
it is provided with a millimeter graduation. This line pq cor-
responds with the zero of the vernier n', which is attached to
MM' and which glides along AB with MM' when the latter



Online LibraryJohn Adolphus FlemerAn elementary treatise on phototopographic methods and instruments, including a concise review of executed phototopographic surveys and of publicatins on this subject → online text (page 22 of 33)