# Curves and intersections don’t match

DELFTship forum Hull modeling Curves and intersections don’t match

• Author
Posts
• #35598
Margus Liigsoo
Participant

Hi!

I do not understand why intersection (ex. station) looks straight as planned, but the curve at the same place can look akwardly bent following the surfave interior edge form. Even if I have a planar surface the curve is wierd in some places. Any explanations?

• #35600
N J Cook
Participant

I sometimes have the same problem. It seems to occur when intersecting the hull with another plane. In my case (see attached image file), adding a floor produces problems with the linesplan sections …. you can see that the second section is kinked upwards near the centreline and other sections have missing segments. If I uncheck “intesections” and “linesplan” for the floor the problem goes away.

• #35603
Marven
Keymaster

I do not understand why intersection (ex. station) looks straight as planned, but the curve at the same place can look akwardly bent following the surfave interior edge form. Even if I have a planar surface the curve is wierd in some places.]

You have to understand the difference between a station and a control curve. A station is a planar intersection of the surface, therefore the resulting curve will always be planar.
A control curve is a curve connecting the limit points, which basically are a projection of the control points on to the surface. Even if all the control points are located on the same plane this does not mean that the points when projected onto the surface are still on that same plane because the normal directions in the control points can be different.

However usually the differences are quite small, except when you use faces with more or less then 4 controlponts. The more points you use for a face, the more twist there will be in the resulting surface. When looking at your model I suspect you have used faces with quite a large number of points. You should avoid this at all cost.

• #35604
Marven
Keymaster

I sometimes have the same problem. It seems to occur when intersecting the hull with another plane. In my case (see attached image file), adding a floor produces problems with the linesplan sections …. you can see that the second section is kinked upwards near the centreline and other sections have missing segments. If I uncheck “intesections” and “linesplan” for the floor the problem goes away.

If the floor is at the same location as the station then the calculated intersection line can show abnomalies. The solution is indeed to disable the layer for the calculation of intersection lines.
In most cases the intersection line of a floor/bulkhead would not provide any useful information.