New railways are built mostly in unsurveyed areas, so it is necessary 
to establish a net of horizontal and vertical ground control for the photogrammetric 
mapping at a scale of 1" - 2400! with 5 ft. contour intervals. This control net is also 
used by the location crews who stake the designed center line on the ground. As 
ground surveys are relatively expensive they are kept to a necessary minimum. 
By employing Tellurometer traversing, permanent points are esta- 
blished on the ground as close as practical to the probable location of the center line. 
These points are established at five-mile intervals. In between, at approximately 
one-mile intervals, positions of additional, identifiable points are established by 
aerial triangulation methods. The use of EK-3 and electronic computers make the 
aerial triangulation with the A-8 economical and relatively simple. In addition to 
points required for the transferring of scale and elevation, the co-ordinates are read 
off for some additional points which can be easily and positively identified on the 
ground. The adjusting of the triangulation strips is done employing the method develc- 
ped by the author (19). The aerial photographs are flown at a scale of 1 : 18,000; 
they are also used for the compilation of locations plans at 1 : 2400 with 5 ft. contour 
intervals. 
When running the location survey on the ground, the field survey 
crew can tie in its surveys to the points established photogrammetrically. The posi- 
tional accuracy of the points determined in this way is comparable to that of a third 
order traverse. For all practical purposes it is adequate for location surveys. 
The advantage of this method, in addition to its speed and economy, 
is that the positions of points are established independently of each other and are not 
subject to an accumulation of errors and compensation of large errors. Difficult 
terrain does not affect the accuracy of this method nor substantially slow its progress. 
4. DETERMINATION OF CROSS SECTION PROFILES AND ELECTRONIC COMPU- 
TATIONS BEFORE CONSTRUCTION 
At this stage of the project, the right-of-way is first cleared and 
grubbed, and then the center line is re-staked. At the same time, the ground control 
for the absolute orientation of stereo-models employed in the determination of cross 
sections is established. 
The center line stakes at 100 ft. intervals are flagged with 1 ft. x 
1 ft. cardboard squares. The permanent control points are located approximately 
150 ft. at each side of the center line spaced about 400 ft. apart. These are flagged 
with wood crosses 5 ft. long and 1 ft. wide, Fig. 6. This ground control consists 
of the center line stakes with known position and elevations and of permanently marked 
points located outside of the cleared right-of-way with known elevations. The posi- 
tion of these permanent controlled points is established photogrammetrically during 
the initial determination of cross sections. The aerial photography is obtained with 
a 6" Avigon lens at a scale which varies from 1 : 3600 to 1 : 4000. 
The procedure for obtaining the cross sections is briefly as 
follows: manuscripts are prepared at a scale of 1 : 600, showing the center line of 
the railway as staked on the ground. The relative orientation of the stereo- model is 
established by employing the optical mechanical method. Particular efforts are made 
to ensure that the area of immediate interest is parallax-free and that it does not 
show any model deformations. In some instances, we have employed numerical 
methods of relative orientation in an attempt to improve the overall quanlity of the 
results. Since only a relatively small portion of the model is measured, we found 
we could not observe any improvement in the accuracy. Therefore, we are employ- 
ing the optical mechanical method.