The Richmond Virginian. (Richmond, Va.) 1910-1920, 1919-06-08
MAPPING FROM THE AIR.
tstndies by the Geological survey

, depend on gravity TO hold the camera
In the REQUIRED position, 10 acteate
level bubbles which shall register the
amount Of tilt or 10 perform some
similar work Such devices are I'M
successful because the movements OF
! the airplsne do not allow gravity tn
i act unhindered. Any device that de-
! ponds wholly on the action OF gravity
| is therefore inadequate. II is likely
! that the svroscope will he utilized In
I solving tho problem Recent expert
. naents with a camera mounted as
pendulum whose movement Is damp
! Ell by EyroScope gave encouraging
1 results bat he errors are still too
great 10 permit The pictures TO ho
used in constructing maps, although
such partly corrected photographs
manifestly have a much greater value
than those that are totally uncof"
rectnd The application ~ the gvro-
scope To the stabiilz9tion Of q re-
ference point from which The devta-
/ tion can hn measured gives promise
Of success, for such an apparatus wl!i
have less work to do than one intend
cd 10 stabilize the whole camera ana
can therefore he made more accurate.
Iirhrer. F4ss ella borate and at mucA
smaller cu%t
Use Of Ee,HfyInr Camera.
IF n 1t stabilized reference point rather
than q stabilized camera is used the
pictures must subsequently he cor
reeted or horizoniali2ed by a trans
forming or reciifying camera Air
plane photographs taken at an in
cltnation to the plano Of the horizon
do not represent objects on any uni
form scale, and the recttfying camera
Ia used 70 give them Uniform scale
throughout An instrument desi gned |
for this purpose in the geological sur
vev has been made and successfully
used by the survey and the corps OF
engineers Of %the army. prelimi- |
nary statement regarding the theory
and use OF this instrument ta given in
A paper bv p n MONT entitled "A
| method OF aero photo gra phic map
wing" IN he published In the Geo
graphical review.
The problem Of flying at any given
altitude in order ~ maintain q uni
form scale in "A series ~ pictures has
beer considered n an airplane flying
At an altitude of about 5000 feet rises
or falls 100 feet while pictures are
being taken the change in altitude In
PRODUCES ar error ~ per cent in the
scale perhaps in two overlapping
photographs In matching UP dis
torted pictures taken with an IN
stabilized camera TO form q mosaic
this change Of scale is indeter ina BE
for each photograph shows differences
IN scale due ~ the tilt of the camera.
and hence differences in scale due 70
difference in altitude can not he recoG-
! ri2od and corrected. In photographs
taken IN a horizontal plane or IN rec
+ '.GcA pictures, however, differenttai
4Chanees Of scale are eliminated, and
| Tic tfYnrre of scare due TO change I'm
! altitude is corrected ny simple en-
! farrentent or reduction. FLYING at a
uniform altitude Ia not therefore o.
primary Importance, but II will do
aWav with much of tho labor Of en-
tzsrEesI,4ent- and reduction.
Corrections for Distortion.
Afnr all tho photographs are hori
zontalized and brought TO the same
scale il is still necessary to make cor
rections for distortion caused by re-
i lief OF the area Prominent eleva-
tons above the general level, such as
hills or mountains, Will appear to be
more distant than they really are.
and depresSions below the general
level will appear 70 he too near In
photographs Of regions of low relief.
such MS our coastal plain, the distor
lion is usually slight but in photo
graphs ~ areas OF moderate or great
or relief & is considerable. A method
Of correcting such distortion Is neces
sary to produce an accurate plan ma y
as we'll as n contour map. An april
cation of the principles Of stereoscopc
vision may furnish such a method
but. II will not afford the only solu
ton Of tho problem.
The whole problem Of photogra phic
surveying from the air Is domtnantly
an engineering problem. Photo
graphic technique is of course an es-
sential part OF the work, but IL is n
! snbnrdinate- part. for the hest photo
graphs are valueless rs map making
material unless they are accompanied
by the requisite engineering data
| Projections. adjustments, and other
details OF map-making technique are
as necessary in photo-aerial surveying
as in other surveying, and ali map
work Of experienced engineers.
In conclusion, II may be said that
Photographic mapping from aircraft
is entirely practicable but Tint It has
not yet been brought to the point
where II can surerse1e ground sur-
veving The science of cartogra ply
will No doubt be greatly advanced
when the aerial method Is perfected,
. but fundamental problems remain to
be solved and this fact should be rec
ognized and all possible energy should
he devoted to the solution of those
} problems. II is hoped that solutions
Of the essential problems in photo
aerial surveying will soon he obtained
and that this method viii be put to
| practical use in map making.