Can't Select Part of Model

[Anonymous]

Found STL for a football stadium that I want to experiment with color. I am trying to select different seat levels to color. The upper part is fine but I can't select the lower level. Out of curiosity, I did control A to get everything, and it's not selected. I can see the wireframe, but it is not grey like everything else. It is a pink color.  Is it somehow locked? 

[Anonymous]

Might be flipped faces' normals? The pink you see is striped? 

If so and it's all over:

CTRL (Cmd on MAC) to SelectAll. Now do Edit/FlipNormals...

Does that fix your issue?

[Anonymous]

Sorry: Of course: Ctrl + A

[Anonymous]

thanks for reply. Pink is just part of model and won't select cntr a. Just found new stl. Crossing my fingers

[Anonymous]

OK, so days later I see that flip normal is part of the problem. I also have some non-manifold issues - that's another story. Re flip normal - when I select all and flip normal, the pink becomes normal, and the normal becomes pink, they just invert. my head hurts.

[Anonymous]

The easy case:

There are several not connected shells combined to one object where some of them are flipped. Something like this (shells might intersect others too):

In this case you can select a some seed selection on the flipped shell (you need to enable AllowBackFaces in SELECT). You can't see this seed selection as it is rendered at the front of the faces only which point to the inside. Hit E ( or do Modify/ExpandToConnected )  and do Edit/FlipNormals.

The harder case:

Flipped faces and faces oriented correctly are on the same shell.

To fix this you need to get face groups for the flipped regions. So do EDIT/GenerateFaceGroups.

Set its mode to NormalAngle and increase AngleThreshold and SizeThreshold to their maximum to get only a small number of groups.

The difference of the normal direction is a maximal one. So NormalAngle mode will create groups for the inverted normals regions.

Go to SELECT and with a small brush and AllowBackFaces enabled double click on a flipped region (a double click expands the selection to the group) Again the selection will not be visible but Edit/FlipNormals should work.

Select the next group and repeat the upper step.

[Anonymous]

Thanks for the incredible detailed response. Still process some of the technical aspects of this information.

[Anonymous]

Hi there. I have the same problem and, after double click and the portion becoming orange, I am unsure what I am supposed to to do make that part that at the start can't be sleectable because it has an opposite normal, to "join" the main part of the body and being both selectable at the same time.

Thanks.

[Anonymous]

You do not want to select front - and backfaces at the same time. Just select backfaces to flip.

To make flipped regions selectable you need to activate AllowBackFaces in the Filters section of the tool's properties. Select faces you are watching from the rear (selected backfaces should be black - not orange - now).

(Without making backfaces selectable you also might select all frontfaces and hit I to invert that selection.)

Now when only backfaces are selected run Edit/FlipNormals (Note: there's EDIT in the left sidebar AND Edit within the SELECT properties as soon as there's some selection. You want to run FlipNormals from the selection Edit). 

[Anonymous]

Hi there. By this option I am only able to switch between the selection, I don't know if I am doing something wrong.

What I'd like to do is to "fix" the normals so then the mesh works as intended and I can select all the model and apply operations to every part.

Thanks.

[Anonymous]

Here's the workflow using GenerateFaceGroups in a screencast