Principle

NB; need a bit more investigation about how cant used for template is calculated.

Credit to Piotr who provided information and video.

Sweep Envelope generation

Sweep Envelope tool calculates approximate corridor swept by rolling stock represented by single coach.

It is not a kinematic envelope calculation tool. It does attempt to calculate true swept corridor including rail head wear or rail side wear or all other parameters defined in respective norms. It calculates only area swept by freely rolling stock. That means calculation in sequential manner location of bogies lying on rails determining 3D position of entire rolling stock item. Sections generated at different stations along centerline being sum of rolling stock item sections in different rolling stock locations and eventually stitching per station generated sections into volumetric mesh representing swept corridor.

Generation of swept section illustrates “SweepEnvelope - single section generation.mp4” animation.

Coach Definition

Rolling stock may be defined in two ways.

Simplified method assumes rectangular shape of rolling stock section (“Longitudinal and rectangle”) more advanced method (“Longitudinal and template”) uses custom rolling stock section.

In order to define 3D model of rolling stock apart of section definition, location of bogies (“Bogie Base”) and front and rear extend of rolling stock from bogie location are necessary.

“Longitudinal and rectangle” method requires also elevation of rectangular rolling stock section above rails.

In “Longitudinal and template” method elevation is derived from rolling stock section definition.

Computation parameters

“Section Interval” (or “Section Sampling”) defines distance between consecutive locations where sections used for generation mesh representing swept extent are generated.

“Coach Sampling” defines locations used for placement of rolling stock used to generate individual mesh sections.

Section interval must always be greater than coach sampling interval.
Example below where coach sampling in x10 section interval. 10 sections are calculated where the coach is not "moving", then new position of coach is defined. That is why we have steps.

Decreasing coach sampling value increases accuracy at each section interval.
Increasing section interval decreases the size of the mesh but decreases accuracy between section interval because it is a straight between section intervals.