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11.13.2 Basic Terms
Elements of a road
project
Road projects consist, in general, of a horizontal and a vertical alignment.
Horizontal geometry
elements
For onboard input Road 3D supports the following elements for horizontal alignments.
Any project point P1 has E, N and Z coordinates in a deter-
mined coordinate system and has three positions.
P1' Position on natural surface
P1" Position on vertical alignment
P1'" Position on horizontal alignment
With a second point P2 the alignment is defined.
P1' P2'
Projection of the alignment onto the natural
surface.
P1'' P2''
Vertical alignment
P1''' P2'''
Horizontal alignment
Grade angle between the vertical and horizontal
alignment.
a Natural surface
b Horizontal alignment
c Vertical alignment
TSOX_108
P1’
P1’’’
P2’
P2’’
abc
P2’’’
P1’’
Element Description
Straight A straight has to be defined by:
• Start point (P1) and end point (P2) with known Easting and Northing coordinates.
P1 Start point
P2 End point
Curve A circular curve has to be defined by:
• Start point (P1) and end point (P2) with known Easting and Northing coordinates.
•Radius (R).
• Direction: Clockwise (b) or Anticlockwise (a).
P1 Start point
P2 End point
RRadius
a Anticlockwise direction
b Clockwise direction
Spiral /
Clothoid
A spiral is a transition curve whose radius changes along its length. A spiral has to be
defined by:
• Start point (P1) and end point (P2) with known Easting and Northing coordinates.
• Radius at the start of the spiral (R).
• Spiral parameter ( ) or length (L) of the spiral.
• Direction: Clockwise or Anticlockwise.
• Spiral type: Spiral in or Spiral out.
P1 Start point
P2 End point
RRadius
LLength
TSOX_109
P1
P2
TSOX_090
P1
R
R
b
a
P2
A =
L · R
TSOX_1 11
R
R
L
P1
P2
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