s experi-
le;
specific
and SPOT
different
tion
e stored
the TTN
R points
ause the
al amount
\R points
cost. For
using the
aE lines,
For the
rtices of
pints.
one foot
Following
lies and
een the
ities of
compila-
je accu-
S more
ligitized
nd it
uate the
compila-
p assume
Accuracy
between
ta with
compiled
n as the
ich geo-
collec-
File are
ig.6 for
to col-
In general, the contours generated with the DTM
data are similar to the contours manually digitized
with the stereoplotter, but a certain amount of
deviation will always exist. The contours generated
with DTM data which were created with REGULAR
points at 25 FT intervals were found to be smoother
and more accurate than the DTM contours from models
using a larger spacing. But this increased accuracy
may not be necessary to some engineering projects,
such as preliminary highway design.
When we look carefully at the comparative contours
in Fig.2, we easily see that the contours generated
by the DTM data file seem to have some significant
discrepancies in the fenced areas labeled A, B, C,
and D.
Case in area A:
Some BREAK lines missed in the right hand side of
the highway resulted in ditch lines missed in the
contours. Fig.3 shows contours generated with DTM
data which were created with REGULAR points at 40
FT intervals and enhanced with additional BREAK
lines.
MANUAL SPACING SPACING
DIGIT. 25FT Diff 40FT Diff
(Elev) (Elev) (FT) (Elev) (FT)
530 529.94 -0.06 530.77 +0.77
540 539.40 -0.60 540.94 +0.94
550 549.19 -0.81 549.16 -0.84
560 559.78 -0.22 559.51 -0.49
570 570.06 +0.06 570.44 +0.44
580 579.56 -0.44 579.79 -0.21
590 589.95 -0.05 589.18 -0.82
600 599.81 -0.19 599.30 -0.70
600 599.61 -0.39 599.13 -0.87
590 589.50 -0.50 589.60 -0.40
580 579.94 -0.06 580.03 +0.03
570 569.63 -0.37 569.28 -0.72
560 559.82 -0.18 560.01 +0.01
560 559.85 -0.15 560.03 +0.03
570 569.68 -0.32 569.66 -0.34
580 579.75 -0.25 579.42 -0.58
590 589.11 -0.89 589.29 -0.71
600 599.28 -0.72 598.99 -1.01
600 600.01 +0.01 600.02 40.02
600 600.19 40.19 599.96 -0.04
600 599.86 -0.14 599.92 -0.08
590 589.95 -0.05 589.98 -0.02
580 579.44 -0.56 579.48 -0.52
570 569.68 -0.32 569.32 -0.68
560 559.47 -0.53 559.5] -0.49
550 549.17 -0.83 549.05 -0.95
540 539.96 -0.04 539.96 -0.04
530 530.33 40.33 530.63 40.63
Diff*Diff 4.0459 9.5184
Standard
Deviation 0.3871 0.5937
SPACING
Case in area B:
Insufficient REGULAR points could not express the
accurate location of the contours.
Case in area C:
This area was covered by heavy forest. The contours
digitized by manual compilation and the contours
generated by the DTM data were both inaccurate.
Case in area D:
This area was covered by light forest. The contours
digitized by manual compilation may be not as
accurate as DTM contours.
SPACING
50FT Diff 75FT Diff
(Elev) (FT)
(Elev) (FT)
529.88 -0.12 530.49 +0.49
540.01 +0.01 540.46 +0.46
549.56 -0.44 548.69 .-1.31
559.83 . -0.17 559.97 .-0.03
571.00 1.00 571.11 «41.11
579.80 -0.20 580.74 40.74
590.02 40.02 590.27 40.27
599.79 . -0.21 598,52 -1.48
599.28 .-0.72 598.08 -1.92
590.02 : +0.02 589,73. -0.27
580.14 +0.14 580.19 . 40.19
569.72 -0.28 569.83 .-0.17
560.00 40.00 560.15 10.15
560.05 40.05 560.03 40.03
569.28 .-0.72 568.82. . -1.18
580.11 . 10.11 579.59 -0.41
589.30 -0.70 589.76 -0.24
599.57 -0.43 599.58 -0.42
599.81 -0.19 600.09 10.09
600.05 40.05 600.60 40.60
599,98 . -0.02 600.57 . 10.57
590.42 10.42 590.07 10.07
579.45 -0.55 579.36 -0.64
569.63 -0.37 568.98 -1.02
559.65 -0.35 559.02 -0.98
548.91 -1.09 549.93 -0.07
540.02 40.02 540.09 40.09
530.35. 40.35 530.53. 40.53
5.2345 15.2552
0.4403 0.7517
REGULAR BREAK SPOT EDGE TOTAL TRIANGLES TIME STANDARD REMARKS
SPACING
FT PTs Pis PTs PTS PTs
25-FT 2954 439 5 170 3568
40-FT 1156 439 5B 170 1770
40-FT-E 1110 575 5 170 1860
50-FT 713 439 5 170 1327
75-FT 313 439 5 170 927
HRs DEVIATION
6883 6 0.3871
3319 3 0.5937
3473 3.6 Enhanced
2439 2 0.4403
1647 1 0.7517
Table.2 Number Of Points For Each Geometric Element In Different Files.
845
