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I have a triangulated mesh (100k+ vertices) of a head. I need to select everything apart from the ears, and reduce the vertex density on that selection by 16x or something.

Here is what I'm dealing with:

enter image description here

I've already asked a question on how to do that and got a very helpful answer: Reducing vertex density as distance from point increases

My problem is selecting the ears. I would like to get a high level of control; simply using box select isn't going to cut it.

So I select a vertex path around one ear:

enter image description here

Now I'm stuck, can someone guide me?

What are the steps I need? This is my guess:

  • somehow store the vertex-path
  • do exactly the same for the other ear
  • now might there be some tool like Microsoft paint's flood-fill, where I just hit one vertex on the skull, and it will select be entire skull up to and including the boundaries I've just created (i.e. it will avoid the ears)
  • then I decimate, which I have instructions for

Is there some tool I can use that will just let me draw on the surface, and then it will figure out an appropriate vertex-path? when I do this on a 2M vertex model, it is going to take ages manually clicking 500 vertices.

EDIT: I got one step further:

enter image description here

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    $\begingroup$ I think youo are asking for how to choose the best selection method in this case, right? If so, I think the WIKI Indroduction for Advanced Selection contains all you need, actually. $\endgroup$ – Leon Cheung Dec 15 '13 at 4:29
  • $\begingroup$ What about using 3D view > Header > Select > Mirror for mirroring the selection? $\endgroup$ – gandalf3 Dec 15 '13 at 4:37
  • $\begingroup$ @gandalf3 Mirror Selection currently requires strictly mirrored elements. I don't think it will work well in the OP's case. $\endgroup$ – Leon Cheung Dec 15 '13 at 7:20
  • $\begingroup$ @LeonCheung Good point, I didn't notice that the OP's mesh was not mirrored. $\endgroup$ – gandalf3 Dec 15 '13 at 17:59
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    $\begingroup$ That is some nasty topography. 3D scan, I take it, right? $\endgroup$ – Keavon Dec 16 '13 at 3:08
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Using circle select rather than box select might make things easier.

C, then click and drag, right-click to exit, middle-click to deselect rather than selecting.

EDIT: You can also use the mouse wheel to change the size of the circle.

(key word here is might, I don't know what the performance is like for you. I'm sure editing a mesh like that wouldn't be fun on my computer.)

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Another way: If you don't mind adding some extra points on the model, you may also consider to separate ears by cutting them off using Knife Cut or Knife Project tool:

enter image description here

enter image description here

PROS: Almost perfect clean separation.

CONS: Add extra vertices to the original mesh. You may judge and weigh if this is acceptable.

Then CtrlG to add those vertices to a new group for the restraining usage in Decimate modifier panel.

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If I was in your situation I would go to Edit more, clicked on Z to toggle to wireframe mode, and used combination of loop select/deselect (Ctrl + Left mouse to add to selected area, Shift-Ctrl + Left mouse to subtract from selected area). It would take a few iterations, but you should get what you want in a minute or so.

Positioning head for the first select so that two ears overlap in your view (for example by toggling to Ortho mode with keypad 5 and to Right view with keypad's 3) would speed things up. After you did first select -- it is better to avoid this exact position, so you do not unselect something you did not intend to.

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One way is to hide the ears.

Once you have the loop around the ears selected

  • press H to hide the selected vertices
  • with the mouse over the ear press L to select all connected visible vertices
  • press H to hide the selected vertices
  • repeat for other side
  • simplify the mesh
  • Press AltH to unhide the ears

You may want to cleanup a bit around the edge that was hidden, but the hidden vertices will not be effected by any editing actions taken on the visible vertices.

You can also hide incrementally, so you can select a few vertices at the tip of the ear, press Ctrlnumpad+ to increase the selection then H to hide them, select some remaining ear vertices, increase the selection and hide them... till you have hidden the area you want protected.

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One way to quickly select a string of vertices is by using the Select Shortest Path tool.

  1. Select two vertices for the end points of the string selection:

    enter image description here

  2. Press Shortest Path in 3D view > Header > Select:

    enter image description here

Result:

enter image description here

It only selects in straight lines, (no curving or circles) but I imagine this could speed up your workflow a bit.

You could use this to select your boundary and use Select Boundary Loop Inner-region.

Do this for both ears, then invert the selection (CtrlI)

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