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Doove

Can't loft: selected entities not valid

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Doove

Hi

 

am trying to loft a series of closed 2d polyline cross sections to create a landscape solid or surface.

 

It will do 5 but selecting anymore causes it to say the "selected entities are not valid".

 

this is the link to the autodesk article http://usa.autodesk.com/adsk/servlet/ps/item?siteID=123112&id=7804217&linkID=9240617

 

but I'm having trouble understanding it. I tried opening all the polylines but that just didn't work.

 

I've tried revsersing the selection order but no go either.

 

I will have a go at planesurf but really I was hoping to loft a solid.

 

Any suggestions?

 

I'll try and post the file but it's pretty big.

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ReMark

Did you try method three?

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Doove

Remark - I'm grateful for your interest, your advice tends to be very sound.

 

I haven't tried PLANESURF yet as I can't really see how that would work. I've attached a pic of model space so you can see what I've done so far.

 

I've converted the 3D polyline contours to 2D closed polyline cross-sections. The bottom one is at z=0. The others are 500 apart in the z.

 

I'm confused as to what Autodesk want me to do for method 1 and 3.

 

Re method 1:

I tried opening the polys but no joy. Do they really want me to explode the lot? I suppose I could use groups to select them...

 

Re method 3:

I thought planesurf created planar surfaces - how is this going to create my 3D mesh?

CAPEL DEWI - 3D - LANDSCAPE SOLID.jpg

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ReMark

How have you been attempting to do the lofting? Do you select every closed polyline bottom to top?

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Doove

Yes. There are 30 in total.

 

I'll have a go at selecting a couple at a time too and using a ruled fit. I don't think doing it in sections would work well as a smooth fit do you?

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ReMark

I would try doing 5 at a time. If if works then boost this to 10 at a time. I think the fit will be OK.

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Doove

It let me do the first four, then another loft but only with the next two. Won;t let me any others.

 

Do you know what Autodesk mean by 'open curves' - do they really mean explode it into lines and arcs?

 

Or have you any advice regarding the planesurf method?

CAPEL DEWI - 3D - LANDSCAPE SOLID - 4 countours and 2 countours.jpg

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ReMark

"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." Could this be the root cause of your problem?

 

Yes, AutoDesk is recommending you explode the polylines into arcs and lines. No longer sure this is a good idea.

 

I'll check into the Planesurf command and get back to you.

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Secretagdan

Four of your polylines are 'self intersecting'. One of them happens to be the 5th line from the bottom up. This is most likely why you are unable to LOFT.

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ReMark

I'm getting some "not valid entities" error messages. I'm working from the top down. How were the contours created in the first place?

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shift1313

I do believe you have locked up my acad:)

 

 

i would try this as a surface loft. Loose the sides and back(if that makes sense). from there you can extrude and use your surface to trim your solid. I looked over the curves and i couldnt see any that were open but the self intersection is a problem. I think part of the issue is acad cant actually produce the geometry since there are sharp corners and smooth in the same transitions.

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Doove

Hello

 

How do you identify a self-intersecting polyline?

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Doove
I'm getting some "not valid entities" error messages. I'm working from the top down. How were the contours created in the first place?

 

Surveyor gave us a 3D topo that used 3D polylines for everything.

 

I took the contours, exploded them and turned them into 2d closed polylines. 3D polys can't be used as cross-sections in loft.

 

At the moment I'm creating regions for each boundary to try and get around the self-intersecting problem.

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Doove
I do believe you have locked up my acad:)

 

You're not trying to tell me a little loft operation has crashed your PC... good old acad... teaches the Way Of Infinite Patience :wink:

 

I'll give the lines a short back & sides and try the surface loft after I've attemted using regions.

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Doove

UPDATE FOR ANYONE TRYING SIMILAR THING:

 

I'm having a great time here. Keeps making bloody autocad CTD.

 

After much mucking around; used boundary to create new 'clean' polylines and regions for first 8 contours.

 

Using polys loft worked for first 5!!!! Then would only do 2 at a time BUT DID DO IT - took an unholy length of time punctuated with many CTDs.

 

Using the regions either CTDs or gives very strange results.

 

Have triEd planesurf - no idea what autodesk are suggesting there, just doesn't work. Tried edgesurf & rulesurf too but these don't give the smooth fit I want, though increasing surftab1 & 2 could approimate something more worthy.

 

Have just now tried the surface loft as suggested by shift1313, this seems to be the best approach so far - thanks shift!

 

It'll do about 5 at a time, though I've only just noticed my isolines are set to 18, 18; 3 times the default of 6,6, so this may be slowing things up.

 

Yes it takes forever! The plan at the moment is to add thickness (0.01) to the multiple surfaces then union them.

 

I'll then extrude a primitive up to the surface and union that.

 

I don't anticpate any problems, it's been sooo easy so far what could possibly go wrong... pray for me...

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Doove

OK - you can stop laughing, I now understand you can't actually DO ANYTHING with surfaces.

 

Can't join, can't thicken, can't trim/extend a solid to them, can't extrude them, etc.

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shift1313

you can convert surfaces/solids in acad07 or newer. If you end up using meshes(dont recommend) you can use the m2s(mesh to solid) lisp which will extrude from your mesh in the z direction using your mesh to trim.

 

Here is a quick example for you. Its a lofted surface using two curves and two straight line guides. I then created a box that went through the surface and used the slice command to slice my solid with a surface.

 

 

You can also thicken your lofted surface to make it a solid, or if you close the surface with other surfaces you can convert that to a solid.

acadslice.JPG

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shift1313

As another note there are several other commands i think that will give you the same result as long as you are using a lofted surface. I dont play around with acad much anymore so ive lost a bit of touch with this. 2010 seems to be much more powerful for this type of stuff but the older versions seem to need a bit of "extra" work.

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Doove

Hi shift, I completely agree that thicken etc is the way it's supposed to work but I can't thicken as "surface is self-intersecting" and can't do anything else as:

 

"The Boolean operation on solids failed.

Modeling Operation Error:

Inconsistent face-body relationships".

 

any idea what this means?

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