The longitudinal profile is a graph (fig. 10.11.) on which are plotted all the points of the natural ground and the axis of the project. It is established in the first place.
We rely on this document for the drawing of the cross section (fig. 10.12.).
Distances and altitudes are given in meters to the nearest centimeter.
In general, a comparison plane is chosen with an altitude lower than the altitude of the lowest point of the project or of the natural terrain.
This comparison plane is the abscissa axis are plotted.
The scales of representation can be different in abscissa and in ordinates (in ratio of the order of 1/54 to 1/10) so as to emphasize the relief which may not appear on a project of great length..
We first draw the natural terrain ( TN ), generally in a black medium line.
Its layout is given by the position of each axis point of a cross section, the natural terrain being assumed to be straight between these point.
At the same time, information is reported in the box at the bottom of the graph: the horizontal distances between cross sections called partial distances, the cumulative distances (also called curvilinear abscissas) since the origin of the project and the altitude of each point.
The calculations of the positions of the characteristic points are reduced to straight-straight, straight-circle or staight-parabola intersections in the reference associated with the longitudinal profile.
Fillings ( in red ) and cattings ( in blue ) can be colored differently.
The fictitious cross sections (zero surface) whose position must be determined (abscissa and possibly the altitude) are the points of intersection between the natural ground and the axis of the project; these particular profiles are useful for the calculation of cubatures.
It is necessary to know their position on the abscissa with respect to the two cross sections which frame them.
Drawing procedure:
1) Choice of the horizontal reference plane (Comparison plane)
2) Define the TN: layout + dimensions
3) Define project: layout + dimensions
4) Number the position of the cross sections
5) Indicate the distances (partial and cumulative)
6) Indicate the slope of the project
7) Indicate the geometric characteristics of the project: alignments and curves (plan view)
Example of a computerized longitudinal profile
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