Cutting a shape in the middle
Posted: 11 February 2019 01:46 PM   [ Ignore ]  
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Hello

I’m trying to find some modeling approaches to create cuts in objects in precise ways.  For example I have an object that is an extruded triangle.  I want to make a cut in each face that is perfectly in the middle
https://www.dropbox.com/s/5tfej1vhe9ft6ju/TriangleCut.c4d?dl=0

Another thing I’m trying to do is to create an extrusion perfectly in the middle of each of the vertical faces of the triangle, but have a hard time figuring out how to identify parametric ways of doing this kind of stuff (or rather, mathematically precise).

Thanks for any insight on how to best to this type of thing

Thanks!

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Posted: 11 February 2019 02:09 PM   [ Ignore ]   [ # 1 ]  
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Hi Alex,

There are indeed several ways to do this. I have recorded the perhaps simplest way. The starting point for the cut is taking from the vertice/point of the triangle. While holding down the Shift key, the cut is straight.

Please have a look at the screen capture below.
https://www.amazon.com/clouddrive/share/1xrvaVJS3114PmJtMrXifHnCkT5DJPe3R07aeXiVZPj

Since we have cut into polygons, some of the points are not separated, hence the extra step.

I’m not clear what you like to extrude from the side polygons. I assume a smaller part of the polygon. While using the short cut M~W, you can use an Extrude inner here. Which can be then scaled. Does this come close to what you had in mind?


As a side note, to work with precision, guides are typically used. Even splines or other objects can be used to support snapping options. Please let me know more about your target so I can answer more in detail.
Thanks as usual for sharing a scene file, that certainly helps a lot!

Tip: Perhaps, instead of splitting in in half, model only half of it and then use a Symmetry Object.
Screen capture
https://www.amazon.com/clouddrive/share/xfFMBSd2WiFrGHtHOrUjhFniGDbRKFkQGwXF8LyJZT3

All the best

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Dr. Sassi V. Sassmannshausen Ph.D.

Photography For C4D Artists: 200 Free Tutorials: Texture, Panorama, HDRI, Camera Projection, etc.
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Posted: 12 February 2019 06:34 AM   [ Ignore ]   [ # 2 ]  
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Joined  2012-01-06

Hi Sassi

Lots of great stuff here!  I had never used the guides, they seem really useful in this case.
I’m going to play around with this stuff today and will come back with any more questions.  Maybe one follow up would be maybe if there is a way to always find the perfect center of a polygon?  I can see that by doing cuts or subdivisions using the opposite vertices is a good technique, but what if the shape is more irregular?


Thanks!

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Posted: 12 February 2019 07:14 AM   [ Ignore ]   [ # 3 ]  
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One more follow up question…
Once I extruded the shape I want from the face of the polygon, I’m trying to assess it’s dimension so I can replicate the same thing with the same size on all sides.
I thought the Coordinates tab would give the correct size of the face, but I’m realizing it isn’t.
In the screenshot below you can see that I used a plugin (MeasureIT) that gives me the distance between two nulls.  I see the value is 81.62cm, but in the coordinate manager the X size is 70.68 in the X axis. 
My axis is not properly aligned in this case, but what is the best way to get dimensions of polygons without having to use measuring tools?

https://www.dropbox.com/s/687s8mlb8e3fha6/2019-02-12_10h11_04.png?dl=0

Thanks!

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Posted: 12 February 2019 11:17 AM   [ Ignore ]   [ # 4 ]  
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Hi Alex,

Thanks for the image. First of all, there is a measuring tool inside of Cinema 4D. Main Menu> Tools> Measure and Construct. One could also use the Distance node in XPresso, or just subtract one vector from another, but I digress.

The center of gravity is typically the most used technique, also called the Plumb-Line method. (Irregular Polygons are not really considered to have a center-point, hence why they are called irregular.) One has to pick up a randomly shaped cardboard and let it hang freely. From the anchor point, a straight line down is drawn. Then this procedure is repeated from another location. Where those lines meet, there is the point of gravity. This can be done in C4D, but it also seems way over the top, in terms of effort.
https://en.wikipedia.org/wiki/Center_of_mass
Scene file
https://www.amazon.com/clouddrive/share/ykcKQStW520yIvdmCmMCSj9LjnMVyDgyuJHq7LghzT3
A more automated process
Scene file
https://www.amazon.com/clouddrive/share/yAcyOp05T03So48y0GekObnSeMQPMSfQdhA2vJ20SvY

We all might remember the Cloner Object setting Mode>Object and its Polygon Center option. Yes, that would give you something, but you asked for a precise method, and this isn’t one. I have set up an example file to demonstrate this.
Scene file
https://www.amazon.com/clouddrive/share/JQ7xYoCvcp6EqfY9SnmmV6pk599vEGOlbP0OvzmBqyV

The Weld Points comes to mind, as there is a central function, but also here, each point has an influence on the result. Which means, that extra points that were added to a straight edge will not change the shape, but the outcome of the point welding will. Similar to that is the Axis Center, it doesn’t really care about the center of gravity.

In the Wiki page (link above) you will find some formulas, but I guess that is beyond the scope of the project. Yes, I checked as well in the “Mathematics for Computer Graphics” book, from John Vince, but he stops short with a triangle example of this problem.

As a side note: The middle point of a polygon has to be on its surface? How about a C-shape (n-gon)for that matter?
Screen shot
https://www.amazon.com/clouddrive/share/6x1W4d5ZlxZQgX3t9YcZE7XESPokPvLNOGkTvn2jon4

I would go with the Cloner Object and perhaps eyeball it.

The question about the dimension, as seen in the image: This is a simple question of setting up the Grid. Select the polygon you like to measure, and then Set the Work-plane to selection. The Coordinates (not the one of the object) will give you the size between points and their position. Set it to World!

All the best

Edited 01:50pm PST

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Dr. Sassi V. Sassmannshausen Ph.D.

Photography For C4D Artists: 200 Free Tutorials: Texture, Panorama, HDRI, Camera Projection, etc.
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Posted: 13 February 2019 07:23 AM   [ Ignore ]   [ # 5 ]  
Total Posts:  151
Joined  2012-01-06

Thanks Sassi

I’ve had problems working with the measure tool in C4d, it always seems very finnicky and working interactively is a bit of a nightmare.  Maybe I’m not understanding it correctly, but anytime I try to use it I feel like I’m fighting with it.  For example snapping to points always seems to be impossible, the tools wants to jump around in different parts of the scene.
Maybe I’m not understanding it well enough…Do you have any recommendations on how to use it?

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Posted: 13 February 2019 09:41 AM   [ Ignore ]   [ # 6 ]  
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Hi Alex,

If I’m not mistaken, you just call it up and click around? Try the key-combinations with it, and it should do what you want.

https://help.maxon.net/us/#TOOLMEASURE

Please let me know if that works for you.

Cheers

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Dr. Sassi V. Sassmannshausen Ph.D.

Photography For C4D Artists: 200 Free Tutorials: Texture, Panorama, HDRI, Camera Projection, etc.
https://www.youtube.com/user/DrSassiLA/playlists

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