Copyright
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 19 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 19 of 33)
Font size
QR-code for this ebook


in Germany.

This phototheodolite, Fig. 138, Plate LXXII, has a centrally
mounted camera K with the transit telescope T on one side and
the vertical circle C on the other side.

The horizontal axis has been widened between the wyes to form
a conical ring R into which the camera K may be inserted. Four
stout springs / press the camera securely against the ring surface,
forming the collar of the conical ring. After insertion into the
ring the camera is revolved, within the former, about its axis until
the end of the screw b abuts against the stop d, when the prin-
cipal line of the negative should be in vertical plane (the horizon
line horizontal).

The camera axis is parallel with the optical axis of the tele-
scope T, both axes being in the same horizontal plane when
they are level. This parallelism between the two axes is per-
manent.

The instrument will be in perfect equilibrium with the camera
either attached or removed.



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 235

The horizontal axis of revolution may be adjusted by means
of the striding level L, which, when required, may be replaced
by a compass very similar to that shown in Fig. 137, Plate LXXI.

Since the telescope (and camera) may be reversed in the wyes
the error of collimation and any index error of the vertical circle
may readily be found or eliminated.

Neither slides nor plate-holders are provided with this instru-
ment, the plates being inserted directly into the carrier of the
camera. This may be done in the field by aid of the packing-
case, Fig. 139, Plate LXXII, specially devised to serve as a dark-
chamber.

The case proper is made of wood with double doors, each
door having a circular opening A, Fig. 139, Plate LXXII, filled
in with a flexible light- and water-tight material, forming sleeves,
in such a way that the hands of the operator may be thrust through
an elastic opening in the center of the apron. The fabric closes
tightly around the wrists, leaving the interior of the case in per-
fect darkness and permitting free play of the hands in the
interior L for manipulating the camera and plates within the
case.

The wooden box is incased in a tight-fitting sole-leather
covering having two flaps 5 to protect the openings A against the
admission of dust when the packing-case is transported on the
back of the instrument-bearer.

The entire instrument, except tripod, may be stowed away
in the case for transportation and safe-keeping. The packing-
box also contains two receptacles K\ and K 2 ; one contains the
unexposed plates and the other receives those that have been
exposed during the day's work.

When an exposed plate is to be exchanged, the camera C,
Fig. 139, Plate LXXII, is placed into the packing-case, and doors,
as well as the leather main flap, are securely fastened, the hands
are inserted into the sleeves A, and the exposed plate P is removed
from the camera and placed into its receptacle KI, closing the
door T. A new plate g, taken from the box K 2 , is placed into



236 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

the camera and its back securely closed, when it will be ready
for another exposure.

The constant focal length of this camera is represented by
the distance between the second nodal point of the lens and the
rear surface of a graduated metal frame permanently secured
to the walls of the camera. The inner edges of this metal dia-
phragm, or frame, bear a centimeter graduation; the middle?
graduation marks of the two horizontal sides locate the prin-
cipal line, while the middle graduation marks of the vertical
sides represent the termini, on the photographic perspectives, of
the horizon line.

The focal length, once determined, remains the same for all
plates. This instrument has been manufactured by F. Rand-
hagen in Hannover, Germany.

The Topographic Bureau of Switzerland has used a photo-
theodolite constructed after the model of Dr. Koppe's instrument.
The experience in Switzerland, however, seems to have decided
the Bureau of Topography not to replace the plane table by the
phototheodolite for general topographic surveys executed by that
bureau.

Dr. C. Koppe's new Instrument and Method for Observing Horizon-
tal and Vertical Angles directly on the Photographic Negative.

We have seen, on page 125, that the iconometric plotting of
vertical and horizontal changes in the terrene were based upon
direct measurements of the coordinates of pictured points. Dr.
Koppe, in his recently published pamphlet on photogrammetry,
with particular reference to cloud photography, has given a new
method having many advantages for particular kinds of work.

He inserts the negative into the camera in the exact position
previously occupied by the plate during exposure and illuminates
the same from the rear sufficiently to bring out all the details of
the negative. With a theodolite telescope directed through the
camera-lens he now observes the vertical and horizontal angles by



SURVEYING- CAMERAS AND GEODETIC INSTRUMENTS. 237

bisecting the particular points on the negative in the same manner
as the surveyor uses a transit for observing in the field.

Light-rays reaching the camera-lens from a distant point in
parallel directions are concentrated and directed to one particular
point on the photographic plate the image point. With Dr.
Koppe's device the same phenomenon takes place only in inverse
order as the light- rays now emanate from the illuminated negative.
Light- rays coming from any point of the negative are refracted by
the camera-lens whence they enter the telescope of the theodolite
in parallel directions. If the telescope had been focused for
infinite distance the pictured point observed upon will appear
sharply bisected by the cross-webs in the telescope, and if the
camera is securely fixed in position and the telescope is now changed
to bisect another pictured point, the angle included between the
directions to the two pictured points successively bisected will
be identical with the angle included between the lines of direction
drawn from the first nodal point of the lens at the original camera
station in the field to the corresponding two points in nature.
We can, therefore, obtain the values for the vertical and horizontal
angles by reading the corresponding verniers of the theodolite in
both positions of the telescope when bisecting the pictured points.

In the practical application of this method two cases are con-
sidered. The camera is either stationary and the observing tele-
scope adjustable in position, or the telescope is stationary and
the camera is adjustable. Dr. Koppe has experimented with both
types of instruments.

If we insert the negative in the camera, giving it the same
position which the plate had during exposure, and if we level the
instrument, giving it likewise the same position which it had
when the plate was exposed in vertical plane, and finally, if we
adjust the observing telescope of the transit to bring its optical
axis in line with the horizontal axis of the camera, we can observe
horizontal and vertical angles by bisecting the pictured points and
noting the vernier readings.

The main difficulty in the practical solution of this problem



238 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

was the necessity of having to give the observing telescope a
decidedly eccentric position to enable the observer to bisect
pictured points at any place of the illuminated negative. The
construction of this instrument, therefore, is more cumbersome
than the ordinary theodolite or transit with centrally mounted
telescope.

Dr. Koppe declares the degree of accuracy attainable in the
application of this method to be the same as when the corresponding
angles were measured in the field with an instrument of equal
size and power. This assertion is based on practical tests and
experimental observations made by Dr. Koppe in connection with
the preliminary survey for the location of the railroad over the
Jungfrau in the Alps.

The principal advantages of this method, compared with
angular measurements made directly in the field, may be found in
the reduction of the field-work, in the possibility of measuring
angles between objects in motion (using instantaneous plates for
this purpose), in locating points of an evanescent character, like
prominent features of distant mountains which may be liable to
sudden disappearance under freshly fallen snow, or which may
be visible only for short intervals, due to the frequent and sudden
formation of "cloud-caps" or " hoods," etc.

An advantage of Dr. Koppe's method against the general
method of measuring the coordinates of pictured points rests in
the fact that correct values for the horizontal and vertical angles
may be obtained from negatives that are not geometrically true
perspectives, owing to distortion produced by imperfect lenses or
lens combinations, as the points of the illuminated negatives will
emanate light-rays from the first nodal point of the objective in
directions identical with those in which they originally arrived
there when the plate was exposed. The instrument used by
Dr. Koppe in his experimental tests was manufactured by Oskar
Gimther, in Braunschweig, after plans and specifications furnished
by Dr. Koppe. It is illustrated in Figs. 140-142, Plates LXXIII
and LXXIV.



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 239

The phototheodolite is essentially the same as has been de-
scribed with a horizontal circle of 14.7 cm. diameter and vertical
circle of 12 cm. Aperture of the eccentric telescope is 27 mm,
with a focal length of 20 cm. and a Ramsden eyepiece magnifying
twenty times. The verniers read to single minutes, admitting
15 seconds to be estimated.

The telescope r, Fig. 140, Plate LXXIII, used for angulation,
in both the vertical and horizontal sense, upon pictured points
has an aperture of 18 mm., a focal length of 8 cm., and its
Ramsden eyepiece magnifies five times.

The focal length of the camera objective (double anastigmat
of Goerz, series III, No. i) is 144.9 mm -

Fig. 140, Plate LXXIII, shows the phototheodolite com-
bined with the telescope r ready for angulation upon the pictured
points of the illuminated negative in camera Q.

Fig. 141, Plate LXXIV, represents the various attachments
required to convert the phototheodolite, as used in the field, into
the form shown in Fig. 140, Plate LXXIII, as used for the angula-
tion in the office. These attachments, of course, need not to be
taken into the field.

For the use in office glass positives are preferably made by
contact printing from the negatives, as it facilitates the identifica-
tion of points for the " angulation on pictured points" if these have
the same appearance regarding light and shadow as the natural
objects which they represent.

To identify corresponding points on two or more positives the
plates are placed side by side on a frame with a reflector below
them. Points selected for angulation are marked by fine a pricks "
made with a needle. Points of reference that have been observed
in the field are marked with red ink, giving identical points the
same designation, and points to be determined by angulation in
the office are marked with* blue ink. A check for the correct
identification of these points may be obtained in the usual manner
by determining their elevations from two or more plates, using, of
course, in this case the vertical angles obtained by angulation upon



240 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

the pictured points with the telescope r, Fig. 140, Plate LXXIII,
in the office.

The " spring frame" P, Fig. 141, Plate LXXIV, serves to
give the various positive plates the positions in the camera corre-
sponding with the positions of the original plates during exposure.
This is readily accomplished by viewing the plate through the
objective of the camera and adjusting the plate, held against the
graduated frame at the back of the camera by means of the spring
frame P, in such a way that the pictured graduation marks coincide
with their corresponding marks on the graduated frame which is
permanently fixed in the image plane of the camera.

From the phototheodolites as used in the field we now
remove the eccentric telescope, including its vertical circle and
circular camera support, from the wyes and replace these with
the telescope r and vertical circle B (Figs. 140 and 141, Plates
LXXIII and LXXIV). The secondary camera support T-t,
Fig. 141, Plate LXXIV, is then secured to the theodolite by
means of the clamp-screws SS, in the manner shown in Fig. 140,
Plate LXXIII, and the camera Q, with positive plate in adjusted
position, is inserted into the circular camera support K (Figs. 140
and 141, Plates LXXIII and LXXIV) and adjusted in posi-
tion so that the first nodal point coincides with the point of inter-
section of the horizontal and vertical axes of rotation of the tele-
scope r.

The positive plate, if well illuminated by diffused light, will
now emanate rays from the marked points in the same direction,
beyond the objective of the camera, as the incident rays origi-
nally emanating from the corresponding points in nature at
the time of the plate's exposure.

We may now proceed to measure the horizontal and vertical
angles of the marked points of the plate with the telescope r,
provided the camera has the same inclination which it had when
the original plate was exposed. This inclination may be estab-
lished by clamping the telescope r in position when the verniers
of the adjusted vertical circle B, Fig. 140, Plate LXXIII, read



SURVEYING-CAMERAS ,AND GEODETIC INSTRUMENTS. 241

the same as the recorded mean value for the inclination of the
camera in the field for the particular plate under observation,
and tipping the camera, first roughly by means of the support /,
Figs. 140 and 141, Plates LXXIII and LXXIV, then with the
slow-motion screw h, Fig. 140, Plate LXXIII, and Fig. 141, Plate
LXXIV, until the principal point of the photographic perspec-
tive is bisected by the cross- webs of the clamped telescope r,
which is then released for the angulation of the marked points
on the positive plate.

Excepting the angulation upon the triangulation and refer-
ence points in the field, the vertical and horizontal angles to any
number of pictured points may be observed in the office by this
ingenious device, by means of which the greater part of the field-
work, when using tachymetric methods, may be transferred
to the office, making such detailed observations independent of
the length of the field season and of the vicissitudes of climate
and weather.

The computations are the same whether such observations
are made in the field or in the office, both methods giving prac-
tically the same results with instruments of this class.

With Dr. Koppe's instrument the angular values were obtained
in both cases within a maximum error of one minute if the
bisected points were not farther away than 3000 m.

H. Phototheodolite Devised by V. Pollack; Manufactured by
R. Lechner in Vienna, Austria.

With this instrument the camera C, Fig. 143, Plate LXXV,
is centrally located and mounted above the horizontal circle.
The telescope F and the vertical circle V are "attached to one
side of the camera, but counterbalanced by the weight G. In
order to reduce the weight as much as possible aluminum has
been used extensively in the construction of this apparatus.
For instance the upright T is made entirely of that metal.

This instrument has been manufactured in two sizes; the
horizontal circle of the smaller one is graduated to 30' and the



242 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

verniers read to i', \yhile the larger one has a circle graduated
to 20' and its verniers read to 20". The telescope F is mounted
somewhat like that of the Danish plane-table alidade.

The adjustment of the horizontal axis of revolution of the
telescope F is accomplished by means of a special striding level.
Clamps and slow-motion screws are provided for both the hori-
zontal and the vertical circles. The telescope has a focal length
of 27 cm. and an aperture of 31 mm. with a magnifying power
of 9 to 1 8 diameters. The telescope is arranged for stadia-read-
ing, and it has 100 as the constant multiplier. The telescope-
level L is graduated either to 10" of 20". The vertical circle
is graduated to 20' and its two verniers read to 20". The
camera proper is made of aluminum and it is provided
with a Zeiss anastigmat. By means of the rack and pinion, z,
the lens may be elevated or depressed by either 30 or 50 mm.,
according to the size of the instrument. The scale /, together
with the vernier n, serves to measure the vertical deviation of
the lens from its normal position. Also this camera is provided
with a metal frame the inner edges of which have either a
centimeter or a 5-millimeter graduation, which is reproduced
upon the negatives. This graduation serves not only to locate
the horizon and the principal line upon the photographic per-
spectives, but it also gives ready means for discovering any dis-
tortion that may arise in the perspective, due to the wet process
of development. The graduated metal diaphragm or frame is
brought into direct contact with the sensitive surface of the film
by a simple mechanical contrivance, in such a way that the
focal length remains constant for all negatives, even if the
plate-holders or plates should vary a little in thickness.



/. Phototheodolite Devised by Pollack and Hafferl.

This phototheodolite is shown in Fig. 144, Plate LXXV.
It has been used under the Imperial General Directory of



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 243

Austrian State Railroads, and it was placed on exhibition during
the Ninth Convention of German Geographers in Vienna
in 1891. This camera has no graduated metal frame, its horizon
and principal line being located by means of a set of four vanes
or index marks, which are pressed against the sensitized film
of the photographic plate by means of a revolving button, a
device similar to that mentioned in connection with the older
pattern of the U. S. Coast and Geodetic Survey camera. The
instrument is leveled by means of two leveling- screws 5, coun-
teracted by two pivots /, Fig. 144, Plate LXXV, which are held
in position by two spiral springs.

K. R. Lechner's Plwtogrammeter.

R. Lechner's photo grammeter is shown in Fig. 145, Plate LXXVL
(Lechner also manufactures Pollack's, Werner's, and Huebl's in-
struments.)

It is a rectangular metal camera, C, of constant focal length,
centrally mounted upon a graduated horizontal circle, K. Two
spirit-levels /, attached to the upper limb of the horizontal circle
(which is graduated into degrees), and three leveling-screws s
serve to adjust the position of the instrument. BI is the vertical
axis of rotation for camera and horizontal circle. The tripod is
set up approximately level, the circular level x being provided
for that purpose.

The camera is connected with the upper limb of the horizontal
circle by four screws. Two of these are in the direction of the
optical axis and serve to adjust the image plate into vertical plane
(the levels / reading zero), the other two are situated in a line at
right angles to the direction of the optical axis; they serve to
adjust the horizon line into horizontal plane.

The objective, O, is a Zeiss anastigmat //i8, and it may be
elevated or depressed by means of a rack and pinion, such dis-
placement .being read on the scale, /, with vernier, n.

A metal frame with inner edges graduated in centimeters is



244 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

also provided for this camera, and a special mechanical device
serves to press the plate (in the plate-holder after the slide had
been withdrawn) against the rear surface of this frame so that
the centimeter scale is impressed on the margin of the negative or
photograph, thus providing the means to locate the horizon and
principal lines upon the perspective and also to eliminate any error
due either to a possible faulty or imperfect registration of the'
plate-holder or due to distortion in the photograph (paper print).

In the middle of the back-board of the camera is an eyepiece
with cross-threads, very similar in arrangement to that described
for Paganini's new phototheodolite, forming a telescope with the
object-glass of the camera. In this case, however, the cross-
threads are attached to the eyepiece and their intersection coin-
cides with the principal point of the perspective.

A dial compass, B, is attached to the upper face of the camera-
box, a being the catch to clamp the needle, or dial, when not in
use.

L. Phototheodolite oj Col. A. Laussedat (new Model).

Col. A. Laussedat'' s latest phototheodolite, manufactured by
E. Ducretet and L. Lejeune, Paris, France, is shown in Figs. 146
and 147, Plate LXXVI. Both transit telescope and camera are
centrally mounted, the latter above the former. The camera may
also be separated from the transit, and by means of a special pivot
or spindle s f j Fig. 147, Plate LXXVI, it can then be mounted
upon the same tripod. The transit may be used for trigonometric
observations after removal of the camera. Fig. 146, Plate LXXVI,
represents the complete instrument.

sss are the three leveling-screws and c\ is the central clamp;
C is the camera and B is the magazine for fifteen plates ;
O is the objective of the camera (it is a rectilinear wide angle lens

of 75 millimeters focal length);

H is the sliding front plate provided with pinion and rack R to
elevate or depress the lens;



SURVEYING- CAMERAS .AND GEODETIC INSTRUMENTS. 245

V is a finder to show the extent of the field covered by the photo-
graphic plate, although a focusing-glass is also provided;
L is the transit telescope provided with stadia wires;
Ce is the vertical circle graduated to 30';
MM are the uprights supporting the horizontal axis of revolution

of the transit telescope and also supporting the camera;
A is the horizontal circle graduated into 30' ; its clamp and slow-
motion screw are shown at P'\
N is the adjustable level, and
D is a long compass, with slow-motion screw and clamp at P,

to read the magnetic azimuth on the horizontal circle .4.
Several loaded magazines, each containing 15 plates, may be
carried with the instrument. The plates may be changed in full
daylight without removing the camera. The plates are 6^X9 cen-
timeters. Enlarged prints are used for the iconometric plotting.
Six plates forming a panorama cover the entire horizon. The
lens is provided with an iris-shutter, and it may be focused for
short distances or infinity by turning a lever over a scale, show-
ing the distances in meters, attached to the front board H, Fig.
146, Plate LXXVI. In Fig. 147, Plate LXXVI, the instru-
ment (camera) is represented with the magazine B removed and
replaced by the ground glass G.

The entire outfit, excepting the tripod, which is carried sepa-
rately, may be transported in a carrying-case (with shoulder-
straps) 39 X 28 X 1 7 centimeters. The weight of the carrying- case,
including instrument (complete), one magazine, and fifteen plates
amounts to 8 kilogrammes.

M . Phototheodolite oj Starke and Kammerer.

This instrument, represented in Fig. 148, Plate LXXVII,
somewhat resembles in construction the phototheodolite of Prof.
Finsterwalder; neither has a vertical circle and both have a
" camera telescope.'*

The camera is mounted on the horizontal circle like a theo-
dolite. An ordinary skeleton tripod supports the three leveling-



246 PHOTOTOPOGRAPHTC METHODS AND INSTRUMENTS.

screws S of the horizontal circle, Fig. 148, Plate LXXVII, and
a central clamp-screw P with spiral spring connects the tripod
with the instrument proper.

H is the horizontal circle, graduated to 20'; its two verniers
with microscopes L read to single minutes.

The vertical axis, terminating in three horizontal arms BI, B 2)
and B 3 , may be adjusted by means of the leveling-screws S and
the cross-levels /i and 1 2 . The plate D, forming the support
for the cross-levels, is firmly attached to the arm B 2 .

E = upper clamp-screw;
M = upper tangent-screw for slow motion ;

jPi, F 2 , and F 3 = three leveling-screws supporting the camera-
box; they rest in the grooves of the three
arms BI, B 2 , and B 3 ;

1 3 and /4 = cross-levels attached to the camera, as shown
in Fig. 143, Plate LXXVIII, which represents
the camera-box viewed from above.

These cross-levels, together with the screws FI, F 2 , and F 3i
serve to adjust the photographic plate into vertical plane.

5 = movable front board, or objective slide;



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 19 of 33)