Graphics Cross Over when Auto-Generate Reporting Points
The following screen captures illustrate a problem with the Location Module that can produce errors. A P-Line station number references every design point. For design points that do not lie on the P-Line, a perpendicular from the P-Line to the L-Line defines the P-Station.
In the first screen capture the current point (cross) is placed on a Report point at P-Station 1509.0. This point is placed on the L-Line where the perpendicular bisector from the P-Line intersects.
In the second screen capture, two Report points have been added (with the CTRL-J function) at stations 1508.1 and 1510.0. The perpendicular lines that define the L-Line position for these points cross so they appear out of order. This causes the road edge and slope stake graphics to double back on themselves (graphics are drawn in order or P-Line Station). L-Line Stations however are calculated correctly.
Although volumes are calculated segment by segment in order of P-Line Stations, the reversed segments end up with negative L-Stn length and therefore negative volume - this correctly accommodates for segments that get calculated more than once. In the screen capture above, segment L-Stn 1508.4-1510.2 gets calculated three times, twice positive (L-Stn 1503.1-1510.2 and 1508.4-1520.2) and once negative (L-Stn 1510.2-1509.3-1508.4). The net result is the same as if they were calculated in the correct order.
Note that either of these extra points alone would have caused a similar error (although reduced). Also note that the point causing the error could have been a Profile point created in the Profile window. A Plan point (or Report point) created with the mouse would not cause this error as the nearest P-Line segment would be used to define the P-Station.
This problem can only occur with horizontal alignment on the inside of a curve in the P-Line. The size of the effect increases with horizontal offset and P-Line curvature.
How to identify the problem
Watch for road edge features that appear to double back on themselves.
Use the Previous/Next Point buttons in the tool bar (Shift-Ctrl-B or N) to traverse the L-Line. The current point will move backward at the problem point(s).
What to do?
Do not Auto-Generate points at very small intervals. Auto-Generate points on survey stations is adequate for most purposes.
If you need to add a few Report points to smooth out a curve, use the mouse in the Plan window.
If you find evidence of this problem remove report points that are close to others in the problem area.
NOTE: Even if the problem occurs , the volumes have been adjusted at the location of the cross-over to take this into consideration. If you look in the Data Window in the area of the cross over you will notice that the volume will be subtracted and then added again to fix the problem.
