Support
Why is the template drawn wrong (spikes, slopes)?
Summary
When defining a segment in MDT, the template may be drawn incorrectly: slopes that come out wrong with irregular spikes, profiles that are not shown, clearing berms or variable slopes that are applied wrongly, or faults in the curved area of a roundabout. Unlike the program closing down (which is solved in Configuration), these cases are corrected by reviewing the definition of the segment itself: invalid slopes, redundant or incomplete platform assignments and elements, badly defined station intervals and platform vectors that are too tight. This article brings together the causes and solutions documented by technical support.
Applies to
MDT — documented cases with no specific version stated by the user. The option names quoted here (Clearing Berms, the Ditch assignment and Analyze assigned station) are kept in MDT 26, according to its reference manual.
Templates and Segments functions (definition of slopes, ditches, berms, variable slopes and platform).
Symptoms
When generating urban templates, one of the slopes (cut or fill) is drawn incorrectly and irregular spikes appear that cannot be removed when changing the roadbed layer between sidewalk and carriageway.
The segment does not show all the profiles.
The clearing berms or the variable slopes are applied wrongly, or the profiles cut across each other on tight-radius curves.
The template is not drawn correctly in the curved area of a roundabout branch.
Cause
Depending on the documented case, the causes are:
The segment has an invalid fill slope assigned (it shows as "multiple", with an assignment containing strange characters at one of the stations).
The segment definition includes redundant or incomplete assignments or elements (an unnecessary station assignment at the origin, platform elements duplicating the ditch, a missing cut slope where the ditch does not cut the natural terrain).
The clearing berms are interpolated when they are not defined by complete station intervals, and platform vectors that are too tight (of the order of 0.001 m) generate rounding errors and overlapping profiles on tight curves.
On complex geometries such as a roundabout branch, the platform definition is insufficient and a more detailed geometric definition is needed.
Solution
Case: irregular spikes and badly drawn slopes due to a "multiple" fill slope
Run Templates > Edit and select the affected segment.
On the "Fill" tab, check whether the value "multiple" appears.
If it does, select the corresponding station and click "Edit".
Find the assignment with strange characters, select it and delete it. After that, the slope is drawn correctly.
Case: the segment does not show all the profiles
Delete the station assignment at the origin if it is not needed; defining the final station is enough.
Delete the platform elements that duplicate a ditch already defined.
Define a new ditch on the side where the cut is missing, intended to cut the natural terrain, and mark it as a cutting element (in the documented case, with a 5 m run at -2 % and a -0.1 m drop).
The ditch you already had defined is a different one: apply it in fill as well and without marking it as a cutting element, so that it is always applied. Steps 3 and 4 refer to two different ditches: the new one cuts against the terrain; the earlier one must be applied across the whole interval.
On the stretches where the ditch runs on too far without reaching the natural terrain, add an extra cut slope.
What that mark does exactly: in the assignment of each ditch, the Cut box makes the ditch be cut at the point where the terrain cuts it. The ditch that must always be applied is left without that mark, and Apply states whether it acts in cut, in fill or in both.
Case: clearing berms and variable slopes applied wrongly
Always define the clearing berms stating the complete station interval (start and end); if they are left open, the program interpolates them and generates an unwanted transition.
Allow more transition margin between platform vectors and at section changes in general: the minimum value the program accepts is 0.005, but to avoid rounding errors and overlapping profiles on tight-radius curves it is advisable not to go below 0.01–0.02 m.
Name the platform vectors according to their actual type (sidewalk, curb, lane, shoulder, berm, and so on) instead of leaving them with generic or undetermined names, especially if you are going to use the roadbed tab.
Check that the "Analyze assigned station" option is enabled in MDT > Utilities > Configuration > Templates.
Case: the template is not drawn properly on the curve of a roundabout branch
Define, for each carriageway curb, an independent horizontal and vertical alignment, and likewise for the centreline of each road and that of the roundabout itself.
Convert those alignments into 3D polylines with the MDT > Utilities > Convert Segment to 3D Polyline utility.
From there, obtain the curbs and the sidewalk by means of a parallel offset.
For complex geometries of this kind it is advisable to contact technical support so that the particular case can be reviewed in detail.
If the problem persists
On urban templates where the problem lies in the subgrade (as well as in the slope), support needs to see the drawing of the section in elevation in order to help.
For berms, variable slopes and roundabout geometries, prepare a simple example and attach your segment and your drawing (DWG) when opening the enquiry: support can edit it and send it back with the corrections so that you can see the differences.
Category: Templates and roadbeds · Level: Intermediate