Problems with Lofting Plines... [Archive]

stusic

2008-07-05, 05:22 PM

I'm having some issues lofting these (closed) polylines. I get this far: I issue the LOFT command, select all 44 closed polylines, choose the CROSS-SECTIONS ONLY option. After this, it seems no matter what options I choose in the Loft Settings dialog box, I get the error "The selected entities are not valid". What am I doing wrong? / How can I create this loft? Any help's greatly appreciated; this is driving me crazy. See attached file for my example.

Thanks!

stusic

2008-07-05, 08:19 PM

From Autodesk Services & Support (http://usa.autodesk.com/adsk/servlet/ps/item?siteID=123112&id=7804217&linkID=9240617):

Error: The selected entities are not valid

Published date: 2006-Aug-09
ID: TS1057979
Applies to:
AutoCAD® 2009
AutoCAD® 2008
AutoCAD® 2007

Issue

When you tried to use the LOFT command to create a surface, you received one of the following errors and the surface was not created:
The selected entities are not valid.
Modeling Operation Error: Surface U and V derivatives are in the same or opposite direction.

Solution

These errors can occur if the objects being lofted are too close together or a loft surface cannot be created using the loft logarithm in the program. You can use one of the following methods to create the lofted surface:
Method 1
Lofting operations can fail with groups of closed polyline cross sections. Breaking the closed loop or exploding the polylines into open curves will often permit the lofting operation to complete successfully.
Method 2
Use the Planar Surface command (PLANESURF) instead of the loft command. This command is ideal for creating terrain surfaces from contour lines.
Method 3
Reverse the order in which the objects to be lofted are selected. The selection order is important during the lofting calculations. Objects can be lofted when they are selected in certain orders.

I haven't been able to get any of these suggestions to work...