I just though about this, there is a way to 'explode' Splines in autocad. Kindof a workaround the limitations of the explode command on a spline. لو عندى spline وعايز افجره ينفع?? نعم حولة الاول الي poly line باستخدام الامر pedit / SPLINEDIT ثم فجرة بامر.

Removes one grouping level at a time. If a block contains a polyline or a nested block, exploding the block exposes the polyline or nested block object, which must then be exploded to expose its individual objects.

Blocks with equal X, Y, and Z scales explode into their component objects. Blocks with unequal X, Y, and Z scales (nonuniformly scaled blocks) might explode into unexpected objects. When nonuniformly scaled blocks contain objects that cannot be exploded, they are collected into an anonymous block (named with a “*E” prefix) and referenced with the nonuniform scaling. If all the objects in such a block cannot be exploded, the selected block reference will not be exploded. Body, 3D Solid, and Region entities in a nonuniformly scaled block cannot be exploded. Exploding a block that contains attributes deletes the attribute values and redisplays the attribute definitions. Blocks inserted with and external references (xrefs) and their dependent blocks cannot be exploded. Crisis Del Software Pressman.

Since it is impossible to trim, split, etc, a spline in Revit, which makes splines kind of useless, maybe the only solution we have left is to export the spline to 'that other program', trim it there, split it, create bpolys, etc, and bring it back to Revit. The only issue with this approach is that you would have to explode the polyline from the imported.dwg, in order to do something with it in Revit, and exploding.dwgs has been highly discouraged in this forum. But I wonder if it would be an issue if it is just one spline and not a complete drawing. I would like to hear more opinions. (I see a storm coming my way, but it is worth asking. Theres no storm coming your way. If you are okay with people importing and exploding one spline in from autocad, thats good.

They wont be doing it here. In fact, they wont be making the spline in AutoCAD here at all. Splines are a hot button issue for me, not because of the CAD vs Revit issue, but because of the real construction issue. I am ALL ABOUT making whatever design you want, however wild, and however crazy. Im also about it getting built. So decide how you want to actually document that spline: Through work points (French Curve style), as arcs, as hundreds of points exported from a third part app with really ugly dimensions, etc. Once you realize the REALITY of how you are documenting and constructing that thing, ill bet drawing the spline FROM the end points that you are trying to trim to, and not actually trying to use the trim tool, gets more than close enough.

You cant trim to a spline, but you can make a spline after the two endpoints are already in place.