Ordinarily, all measurements of elevation and of horizontal
position for specifically designated points, such as spot elevations
and profile and cross sections, should comply with the requirements in
Table 3.
TABIE 3
ACCURACY OF RANDOMLY MEASURED SPOT ELEVATIONS, AND OF PROFILES
AND CROSS SECTIONS MEASURED PHOTOGRAMMETRICALLY FOR HIGHWAY DESIGN
AND FOR COMPUTING CONSTRUCTION PAY QUANTITIES
Error as Fraction of Flight Height
Average Root | For 90% of
(Arithmetic| Mean |Measurements,
Use and Condition Mean) Square|Not Exceeding
Pay quantities,
open &ground,
uniform slopes 1:18,000 |1:6,000 1:3,600
Pay quantities,
open ground,
irregular slopes 1:15,000 11:5,000 1:3,000
Preliminary quantities,
open ground,
gentle slopes 1:12,000 |1:4,000 1:2, 400
Preliminary quantities,
interferring ground
cover, rolling to
rugged slopes 1:9,000 1:3,000 1:1,800 1:900
Photogrammetric Determination of Supplemental Control--For all
preliminary surveying in the highway field, photogrammetric methods of
determining supplemental control have proven to be adequate. This is
so whether or not the control is determined by analog methods or by
analytical triangulation using aerial photographs of adequate scale.
The analytical triangulation, of course, has become feasible with the
development of precision comparators, availability of point marking and
transfer instruments, and the use of electronic computers. In a
practical sense, it is possible to achieve accuracies which are ade-
quate for photogrammetric compilation of topographic maps, making
profile and cross section measurements, random and coordinate grid spot
elevation measurements, and X, Y, and Z measurements of points on
property boundaries. The acceptable error tolerances for photogram-
metric analog bridging can be expressed as a fraction of the photog-
raphy scale. Such has been done in writing specifications which admit
the use of analog bridging methods. The subsequent tabulation, Table 4,
titled "Error Tolerances for Analog Bridging" summarizes the tolerances
acceptable when error is expressed (1) as a fraction of the photography
scale in feet per inch, and (2) as a fraction of the denominator of the
representative fraction expressing photography scale.
