Transformation
Characteristic
Description
•
Fits much better over larger
areas than a Onestep transfor-
mation. Reason:
The first step of a Twostep transfor-
mation avoids any distortions
because the preliminary grid coordi-
nates are built on a different ellipsoid
than the local points. The second
step ensures that the influence of
the map projection scale factor is
taken into account before the final
2D transformation is computed.
Disadvantage
•
The local ellipsoid must be
known.
•
The map projection must be
known.
•
A pre-transformation must be
known. A null transformation can
be used.
•
In order to obtain accurate ellip-
soidal heights, the geoid separa-
tion at the measured points
must be known. This information
can be determined from a geoid
model.
I.21
U
I.22
V
The vertical alignment gives information about the pattern of heights of the
road axis as it is defined in the horizontal alignment.
A vertical alignment is comprised of the elements:
•
tangents (straight segments)
•
curves
•
parabolas.
Each element involved is defined by individual vertical design elements such as
chainage, Easting, Northing, radius and parameter P.
I.23
W
WGS 1984 is the global geocentric datum to which all GNSS positioning infor-
mation is referred to.
I.24
X
I.25
Y
I.26
Z
Vertical alignment
WGS 1984
Glossary
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