Support
How crowns are defined and applied in the template
Summary
The crown is a change of slope that the program applies in cut from a given distance to the terrain. Recurring questions come up when defining it: why the crown slope cuts against the terrain without deducting the topsoil, why the crown is not applied at every expected station, and how to make its application conditional on the height of the cut slope. This article gathers the cases documented by support and how to solve each one.
Applies to
MDT 9
MDT 25 (Professional) and MDT26
Symptoms
The crown slope cuts against the terrain without deducting the topsoil, and does not match the template that was defined.
The crown is not applied at every expected station, even though the terrain is a short distance away.
You want to make the application of the crown conditional on the height of the cut slope (for example, only when it exceeds 4 m).
Cause
To build the crown, at each station the program draws a parallel to the terrain in cut, downwards, according to the "Distance to Terrain" specified, and the crown is only applied when that parallel lies in cut. Whether the slope cuts against the natural terrain or against the cleared ground depends on a configuration option. Making the crown conditional on the height of the cut is not automated in MDT 9 or MDT 25; in MDT26 there is a configuration option that solves it.
Solution
Case: the crown slope cuts against the terrain without deducting the topsoil
Specify what the slope must cut against — the natural terrain or the cleared ground — in Utilities > Configuration, Templates section: with the option that builds the section slopes from the geology layer enabled (Templates from Topsoil), the slope is thrown against the natural terrain; disabled, against the cleared ground.
Bear in mind that, when defining the crown, the distance to the terrain is the vertical distance from the slope contact at which the crown is thrown with the slope indicated. Check the value of the crown slope: very high values (20H:1V, for example) produce extremely flat crowns.
If what you need is a berm with a gradient and a ditch located just below the topsoil layer, you can define it in the Safeguard tab of the segment edition/definition.
Case: the crown is not applied at every expected station according to the "Distance to Terrain"
To build the crown, at each station the program draws a parallel to the terrain in cut, downwards, according to the "Distance to Terrain" specified. If the result of that parallel is not in cut, the crown is not applied at that station and the normal cut slope is drawn instead.
If you need the opposite behaviour (applying the crown slope precisely when the cut height is less than the distance indicated), it can be achieved by defining two cut slopes assigned by geology layer, instead of using the crown: with the Geology stretching type, the slope is extended to the geology layer you specify. The crown is the simplest and most direct way to obtain the usual result; this other one is what allows the condition to be inverted. If you want the detail applied to your own case, contact support attaching your segment.
Case: making the application of a crown conditional on the height of the cut slope
In MDT26 this condition is automated. Enable Minimum Height for Applying a Crown in the Templates configuration: the crown will only be applied if the cut reaches the minimum height indicated. That height is measured from the slope starting point to the ground elevation at the same offset distance from the centreline.
In MDT 9 and MDT 25 it is not automated. The manual procedure recommended by support is:
Obtain a report with Setting Out > Set Out Lines…, including for example the lines of the roadbed base and the contacts with the final proposed surface.
Analyse the report (in Excel, for example) to calculate the difference in height and filter the stretches where the condition is met (height > 4 m in the documented case).
Apply the crown only in those station intervals in the crown application list of the template.
Support recorded this condition as an improvement planned for MDT 26, and it is available in that version. The remaining crown parameters (Type, Slope, Station, Distance to Terrain and Side) do not change: the height condition is added from the configuration.
If the problem persists
Check the Aplitop video library and its YouTube channel, where there are videos on defining templates, slopes and crowns.
Contact Aplitop technical support attaching the segment file, your licence number and a sketch or screenshot of the result you need to obtain: in several of the documented cases support returned the modified segment or a video with the exact procedure.
Category: Cross sections, slopes and platforms · Level: Intermediate