Notes on Cross-Section Templates
This topic contains additional notes on creating cross-section templates to be included in a Road file.
Sample Elimination Process
When you select to export a Road file, the software slices the model at each specified interval in the horizontal alignment, or at each surface control point, depending on your selection in the Template generate method field. Each of these slices represents a cross-section sample that can be used to create a cross-section template to be included in the Road file. The software then uses a two-step process to determine which samples should be used to create cross-section templates and which should be eliminated. By preventing the creation of unnecessary redundant templates, the size of the export file can be greatly reduced.
- Step 1 - The software identifies each sample that could be eliminated based on a comparison with the sample that immediately precedes and follows it. Three types of comparisons are made:
- Number of points - If the number of points varies, the sample is not eliminated and a cross-section template is created.
- Point names - If the point names vary, the sample is not eliminated and a cross-section template is created.
- Point offset/elevation coordinates - Beginning with the first point in each sample, the software draws a line from the offset/elevation coordinate of the first point on the first sample to the first point on the third sample. It then checks whether the first point on the second sample is within the tolerance (specified in the Tolerance to prevent redundant templates field) of the line. This is repeated for all points on the samples. If any of the points on the second sample are not within the tolerance of the lines defined by the first and third samples, the sample is not eliminated and a cross-section template is created.
If the number and names of points in a sample do not vary from the preceding and following samples, and the point offset/elevation coordinates for the sample are within the specified tolerance when compared to the preceding and following samples, the sample is considered for elimination. Whether it is actually eliminated or not depends on the outcome of step 2.
- Step 2 - The second step is to identify bulges in a long series of samples marked for elimination in step 1. The software looks for a sequence of two or more samples marked for elimination in step 1 and processes them by expanding the number of samples checked for tolerance until the delta is outside of tolerance or the end of the sequence is reached.
The following table illustrate the two steps used to eliminate unnecessary redundant samples, preventing the creation of cross-section templates from those samples.
|
Step |
Pass |
Begin sample |
Samples checked |
End sample |
Passed |
Sample status |
|
1 |
1 |
1 |
2 |
3 |
Yes |
- |
|
2 |
1 |
1 |
2, 3 |
4 |
Yes |
- |
|
2 |
1 |
2, 3, 4 |
5 |
Yes |
- |
|
|
3 |
1 |
2, 3, 5 |
6 |
No; out of tolerance |
1 - Keep 2 - Remove 3 - Remove 4 - Remove 5 - Keep |
Note: To avoid possible errors, when line sampling is based on surface control points, additional samples are created before and after each control point based on the tolerance entered in the Tolerance to prevent redundant templates field.
500-Hundred Sample Threshold
If Sample interval was selected in the Template generate method field, a 500-hundred sample threshold is used to limit the number of sample slices that are held in memory. If 500 or less samples exist in the model, the sample elimination process takes place only once. Otherwise, the elimination process repeats each time the 500-sample threshold is reached. The net result is that a template is created at the beginning of each group of 500 samples. Note that this template might not have been created had the entire model been exported without the 500-hundred sample threshold.
Cross-section Template Naming Convention
Cross-section templates are named sequentially. The format is the selected format for stationing, using five decimal places regardless of the decimal selection in the Project Settings dialog. A template is located on either the left or right side of the center line. The letter “L” is appended to the end of the station identifier when it is on the left; the letter “R” is append when it is on the right. For example, a typical template name might be 1+000.00000L or 1+500.00000:1R.
Rules for Writing Template Elements
By default, template elements are written as cross slope and offset. If the cross slope is greater than 0.9 or the offset is very small, a delta elevation and offset element are written instead. If the difference between the vertical alignment elevation and the surface elevation is greater than the specified tolerance, a delta elevation and offset element are included at that station and all preceding stations in the processing segment, and in all following templates. The delta elevation is the difference between the vertical alignment elevation and the surface elevation. The offset is 0.
