Scenarios on Moving VPIs

Scenarios:

Editing a linestring that has vertical points of intersection (VPIs) can occasionally affect the stations of those VPIs in unexpected ways. In general, if the 2D (x,y) coordinate of a VPI on the linestring is still on the linestring after the edit, the VPI is updated with the new station value, if any. In two instances, the VPIs are not updated with new station values:

  • The linestring is edited outside of the Edit Linestring command; e.g. if a named point that the linestring references is moved, the VPIs are not adjusted.
  • The edit changes the order of the VPIs on the linestring; the VPIs are not adjusted. See the fourth scenario below.

Note: If you change the length of a linestring’s first segment, any vertical points of intersection (VPIs) along the linestring retain their correct distance along the linestring. When making edits affecting the geometry of a linestring, adjustments are made to the distance along values associated with VPIs located on unaffected segments, thereby maintaining their former relative position along those segments.

Here is a linestring with horizontal segments denoted by lettered end points and VPIs denoted by numbers.

  • If you have horizontal segments with VPIs on them, and you move the end point labeled C:
    • VPI 1 is adjusted (the station is actually unchanged)
    • VPIs 2 and 3 are not adjusted (the stations remain the same)
    • VPI 4 is adjusted (the station is changed)

  • If you have horizontal segments with VPIs on them, and you delete the B to C segment:
    • VPI 1 is adjusted (the station is actually unchanged)
    • VPIs 2 and 3 are not adjusted (the stations remain the same)
    • VPI 4 is adjusted (the station is changed)

  • If you have horizontal segments with VPIs on them, and you add the F to A segment:
    • VPIs 1, 2, 3, and 4 are adjusted (their stations are changed)

  • If you have two horizontal segments with VPIs on them...

...and you move the A end point to a location that would change the order of the VPIs:

  • VPIs 1 and 2 are not adjusted (the stations remain the same)