Hello,
I cannot trim or split this planar surface,
I put the file in annexe,
Pb_split_Surf.3dm(364.6 KB)
any idea?
thanks 
Hmm- seems OK here- do you get a closed curve if you Intersect the two objects? What build of Rhino (help > About Rhinoceros)?
pb_split_surf_PG.3dm(367.8 KB)
-Pascal
Hi Pascal, 
when I intersect, I get " Open polycurve with 11 curve segments.".
this is strange because I extruded that surface from a closed curve (actually it was an open curve but I blended them and joined into 1 curve)…mmh…
Kind Regards,
PS:I use Rhino 4
PS2: the details of the curve from which I extruded that polysurface:
Geometry:
Valid curve.
Closed polycurve with 116 curve segments.
Segment 1:
Open NURBS curve
start = (-3992.9,-8461.57,9010)
end = (-3992.9,-8461.57,9010)
degree = 5
control points: non-rational, count=6
knots: uniform (delta=1), domain = 0 to 1
clamped at start and end
Segment 2:
Open NURBS curve
start = (-3992.9,-8461.57,9010)
end = (-4774.83,-8141.18,9010)
degree = 3
control points: non-rational, count=12
knots: non-uniform, domain = -845.119 to 0
clamped at start and end
Segment 3:
Open NURBS curve
start = (-4774.83,-8141.18,9010)
end = (-5453.9,-7822.36,9010)
etc…