The index comprises a series of records that each contain a number of fields.
There are two types of records:
At each cross-section location on the road, there is one chainage record that contains the details about that particular position on the road. At the same location, there may be up to one hundred and twenty eight layer records.
Each layer record contains the information that controls the way areas are formed with that layer. Most options in the Road menu retrieve certain items from the index and write others into it. If Use Index is chosen in Area/Volume, all the required items are retrieved. As an example, by editing the template number a different template would be applied, and by changing the batter flag from '1' to '0' new batters would be appended to the existing ones, and so on. Remember that layer 128 is reserved for the long section elevations.
In the same way that Survey Editing makes fundamental changes to the terrain database, the Index functions can have serious repercussions on the road data. It is recommended that you back up the relevant road data file manually before making any changes.
A Chainage record contains the following fields:
Chainage - the actual chainage value.
H Ordinate - the horizontal ordinate for the chainage point.
V Ordinate - the vertical ordinate for the chainage point.
Skew - the angle from the normal for cross-section extraction.
On/Off flag - enables the chainage to become invisible to routines. A value of '1' switches the chainage off.
A Layer record contains the following fields:
Area Indicator - the type of areas calculated in Area/Volume when this layer was last used as the batter layer (see below).
Template Number - the template number set in Edge Levels when edge levels were generated for this layer.
User Code - reserved for future use.
Batter Flag - flag to indicate that batters are present (see note below).
Left Cut Slope - of left cut batter (1:nn).
Left Fill Slope - of left fill batter (1:nn).
Right Cut Slope - of right cut batter (1:nn).
Right Fill Slope - of right fill batter (1:nn).
Left Cut min offset - from CL for the toe of the left cut batter.
Left Fill min offset - from CL for the toe of the left fill batter.
Right Cut min offset - from CL for the toe of the right cut batter.
Right Fill min offset - from CL for the toe of the right fill batter.
If the Batter Flag is set to '1', batters are assumed to be present and would first be removed and then re-calculated when areas are run in Area/Volume. If set to '0', it is assumed that batters are absent. When areas are run, new batters are appended to the extremities of the cross-section as it stands.
The Area Indicator value controls the way the banks are created:
0 - Bypasses the section altogether.
1 - A normal template addition.
2 - Calculates batters (no template added).
3 - A dump calculation (base connection).
4 - Forces a join of the layer extremities.
5 – A dam calculation.
6 – An area calculation only.
The indicator values, batter slopes and template numbers used, are those recorded by the last area calculation.
See Also Road Index - General.