How to avoid unwanted or badly represented vertical transition curves when converting polylines into a grade line

Summary

When converting a polyline into a grade line, or when drawing the compound long section, MDT may insert automatic vertical transition curves that you do not want, label null-curve tags (KV=0.000) at vertices with no actual curve, or reject the arcs of the polyline. Nearly all of these behaviours are controlled from the long sections configuration (the Automatic transition curve check box) or from a variable of the general configuration file. This article explains how to adjust them.

Applies to

• MDT — applies to MDT 9, MDT 25 and MDT 26 (configuration command mdt25_conf_todo on MDT 25 and mdt9_conf_todo on MDT 9; the behaviour of the automatic transition curve was checked by support).

• Long sections module (one of the cases comes from a water supply network project).

Symptoms

• Converting a polyline into a grade line inserts automatic transition curves that are not wanted; in one case they kept appearing even after switching the option off.

• The compound long section shows KV=0.000 tags (or entry/exit tangent labels) at vertices where there is no actual curve.

• When converting a polyline containing arcs, the program warns that the arcs will not be converted (parabolic grade line) or that two consecutive vertices with curvature are not allowed (circular grade line).

Cause

It depends on the case:

• The Automatic transition curve check box is enabled in the long sections configuration; or a command other than the polyline-to-grade-line conversion is being used, and that conversion is the only one that honours the setting.

• A configuration variable makes the program draw a curve (and its tag) at every vertex, even when it is null.

• A grade line cannot contain polyline arcs unless the parameters of the transition curves are known.

Solution

Case: converting a polyline into a grade line inserts unwanted automatic transition curves

1. Go to MDT > Utilities > Configuration > Long Sections.

2. Clear the Automatic transition curve check box.

3. Convert the polyline into a grade line again: the curves will no longer be inserted (behaviour checked by support on MDT 25; it applies to MDT 26 as well).

If curves are still generated after clearing the box, you may be using a different command to define the grade line: contact support stating the exact command you run.

Case: KV=0.000 tags (or tangent labels) appear at vertices with no actual curve

When the grade line has no transition curves, the compound long section may still label a box with KV=0.000 at every vertex, or entry and exit tangent labels. A configuration option makes the program always draw a curve at each vertex:

1. At the command line, run the general configuration command for your version: mdt25_conf_todo (MDT 25), mdt9_conf_todo (MDT 9) or mdt26_conf_todo (MDT 26).

2. Find the variable that controls the drawing of null transition curves and set its value to 0. On MDT 25 and MDT 26 it is Perfiles/RasanteDibAcuerdosNulos. On MDT 9 the dialog is the same, but the name of the variable is not documented: look for it in the Perfiles section of that dialog.

3. After entering the value, press Enter and then the OK button.

4. Grade lines with null transition curves will no longer show either the curve or the tangency points.

Case: the arcs of a polyline are not converted into a grade line (water supply network)

When converting a polyline containing arcs, the parabolic option warns that the arcs will not be converted (it draws them as straight lines) and the circular option does not accept two consecutive vertices with curvature. An arc cannot be part of a grade line unless the parameters of the transition curves are known.

1. Before converting the grade line, switch off the automatic transition curves: Utilities > Configuration > Long Sections, Automatic transition curve check box.

2. To get the closest possible result, discretize the arcs of the polyline before converting it — every 0.5 m, for instance (the smaller the value, the higher the precision) — with the Discretize Polylines command, among the MDT contour and mapping utilities.

3. Once the polyline has been discretized, convert it into a grade line.

4. If the pipeline needs a trench section with a pipe, define the corresponding trench; support has a video and an example showing how to do it.

If the problem persists

• If you clear the Automatic transition curve check box and curves are still generated, tell support the exact command you use to define the grade line: that command may not honour the setting.

• Contact Aplitop technical support stating your MDT version and a screenshot of the behaviour.

Category: Long sections · Level: Intermediate