Intention:

Using the "Difference" function to create caves and tunnels inside a
square-shaped piece of Martian surface (a hollow mesh object).

What are your solutions, to transfer what is now a mesh, into a solid
object. I believe these objects need to be solid, in order to create
caves and tunnels through Difference into that body.

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On 19-8-2017 8:04, Sven Littkowski wrote:
> Intention:
> 
> Using the "Difference" function to create caves and tunnels inside a
> square-shaped piece of Martian surface (a hollow mesh object).
> 
> What are your solutions, to transfer what is now a mesh, into a solid
> object. I believe these objects need to be solid, in order to create
> caves and tunnels through Difference into that body.
> 

Once thing you can do is an intersection with a slightly smaller box in 
the horizontal directions, and as deep as you want downward. This 
creates the subterranean world.

-- 
Thomas

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On 19/08/2017 07:04, Sven Littkowski wrote:
> Intention:
> 
> Using the "Difference" function to create caves and tunnels inside a
> square-shaped piece of Martian surface (a hollow mesh object).
> 
> What are your solutions, to transfer what is now a mesh, into a solid
> object. I believe these objects need to be solid, in order to create
> caves and tunnels through Difference into that body.
> 


You are thinking about it wrongly.
There are no solid mesh objects. The keyword "hollow" has nothing to do 
with an object not being solid. It is used for media containers.
You should think in terms of the mesh not having any holes. Then you can 
use it with csg without artefacts. In the animation below I intersected 
the mesh of Ariel (the ghost) was intersected with a cub then filled 
with media. The hollow keyword was used for that.

http://www.tc-rtc.co.uk/member/imagenewdisplay/index176.html

When I was creating the df3s for Dhalgren with Thomas. I had a lot of 
trouble with the meshes when they had holes in them. (I had to manually 
edit the slices that make up the image sequence.)

http://news.povray.org/povray.binaries.images/thread/%3C58343a6a@news.povray.org%3E/



-- 

Regards
     Stephen

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Am 19.08.2017 um 08:04 schrieb Sven Littkowski:
> Intention:
> 
> Using the "Difference" function to create caves and tunnels inside a
> square-shaped piece of Martian surface (a hollow mesh object).
> 
> What are your solutions, to transfer what is now a mesh, into a solid
> object. I believe these objects need to be solid, in order to create
> caves and tunnels through Difference into that body.

The solution has been mentioned multiple times already: In POV-Ray, a
`mesh` or `mesh2` object is considered solid if (and only if) it has a
(non-null) `inside_vector` parameter.

The parameter value needs to be a direction, but the actual value is
usually irrelevant as long as the mesh is closed.

If the mesh isn't closed and has holes, using an `inside_vector` will
cause artifacts in CSG operations: Essentially, any hole is extruded to
infinity in the direction opposite to the `inside_vector` direction,
except that these extrusions don't have visible surfaces and just
interact in CSG.

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On 19/08/2017 09:34, clipka wrote:
> The solution has been mentioned multiple times already:

It might be an idea to write it in German.

-- 

Regards
     Stephen

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On 19-8-2017 9:59, Thomas de Groot wrote:
> On 19-8-2017 8:04, Sven Littkowski wrote:
>> Intention:
>>
>> Using the "Difference" function to create caves and tunnels inside a
>> square-shaped piece of Martian surface (a hollow mesh object).
>>
>> What are your solutions, to transfer what is now a mesh, into a solid
>> object. I believe these objects need to be solid, in order to create
>> caves and tunnels through Difference into that body.
>>
> 
> Once thing you can do is an intersection with a slightly smaller box in 
> the horizontal directions, and as deep as you want downward. This 
> creates the subterranean world.
> 

After reading Clipka's answer below, you do not strictly need to do what 
I suggested in the first place but it can help to show the 
'subterranean' boundaries of the landscape mesh.

So, just make differences with any object you need: a cylinder for 
instance as a tunnel entrance.

-- 
Thomas

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Another point I forgot to mention: you may have noticed when in Poseray 
or when rendering in POV-Ray, that the Martian landscape does not have 
the usual left-handed orientation (X-right, Y-up, Z- screenwards) but a 
right-handed one (X-right, Y-screenwards, Z-up). You can easily remedy 
that in Poseray. After you recalculated the normals in the Groups 
folder, first press the 'Flip Y-Z axis' button, then in the Transform 
section, set Scale z to -1 and press the 'Transform' button. Finally, 
export to POV-Ray.

-- 
Thomas

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On 19.08.2017 04:23, Stephen wrote:
> On 19/08/2017 07:04, Sven Littkowski wrote:
>> Intention:
>>
>> Using the "Difference" function to create caves and tunnels inside a
>> square-shaped piece of Martian surface (a hollow mesh object).
>>
>> What are your solutions, to transfer what is now a mesh, into a solid
>> object. I believe these objects need to be solid, in order to create
>> caves and tunnels through Difference into that body.
>>
> 
> 
> You are thinking about it wrongly.
> There are no solid mesh objects. The keyword "hollow" has nothing to do
> with an object not being solid. It is used for media containers.
> You should think in terms of the mesh not having any holes. Then you can
> use it with csg without artefacts. In the animation below I intersected
> the mesh of Ariel (the ghost) was intersected with a cub then filled
> with media. The hollow keyword was used for that.
> 
> http://www.tc-rtc.co.uk/member/imagenewdisplay/index176.html
> 
> When I was creating the df3s for Dhalgren with Thomas. I had a lot of
> trouble with the meshes when they had holes in them. (I had to manually
> edit the slices that make up the image sequence.)
> 
> http://news.povray.org/povray.binaries.images/thread/%3C58343a6a@news.pov
ray.org%3E/
> 
> 
> 
> 
Thanks. The first link requires a username and password, was not able to
see the animation just like that.

Nonetheless, good to know I can still work with division. Will give a try.


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On 19.08.2017 04:34, clipka wrote:
> Am 19.08.2017 um 08:04 schrieb Sven Littkowski:
>> Intention:
>>
>> Using the "Difference" function to create caves and tunnels inside a
>> square-shaped piece of Martian surface (a hollow mesh object).
>>
>> What are your solutions, to transfer what is now a mesh, into a solid
>> object. I believe these objects need to be solid, in order to create
>> caves and tunnels through Difference into that body.
> 
> The solution has been mentioned multiple times already: In POV-Ray, a
> `mesh` or `mesh2` object is considered solid if (and only if) it has a
> (non-null) `inside_vector` parameter.
> 
> The parameter value needs to be a direction, but the actual value is
> usually irrelevant as long as the mesh is closed.
> 
> If the mesh isn't closed and has holes, using an `inside_vector` will
> cause artifacts in CSG operations: Essentially, any hole is extruded to
> infinity in the direction opposite to the `inside_vector` direction,
> except that these extrusions don't have visible surfaces and just
> interact in CSG.
> 
Thanks. Yes, I remember to have read it before. Just, how to define such
a non-zero parameter? I never did that before. As I understand, the
location can be anywhere inside the mesh body.

And in case there are gaps, is there any program that can close any open
gaps in meshes, POV, obj, 3DS, whatever format?

---
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Am 19.08.2017 um 13:11 schrieb Sven Littkowski:

>> The solution has been mentioned multiple times already: In POV-Ray, a
>> `mesh` or `mesh2` object is considered solid if (and only if) it has a
>> (non-null) `inside_vector` parameter.
...
> Thanks. Yes, I remember to have read it before. Just, how to define such
> a non-zero parameter? I never did that before. As I understand, the
> location can be anywhere inside the mesh body.

I repeat: `inside_vector` is NOT a location, but a direction.

That direction is used in a test to answer the question "is location P
inside the mesh?", but that location P is nothing /you/ need to worry
about: POV-Ray of its own accord will come up with plenty of values for
P that it will want to subject to this test.

As for wondering "how to define such a non-zero parameter", that's the
equivalent of searching the "any" key on your keyboard: Literally /any/
vector parameter other than `<0,0,0>` will do. For example:

    mesh2 {
      ...
      inside_vector y
    }

Alternatively, instead of `y` you could also use `z`, or `x`, or
`<5,4,3>`, or `<sin(42*pi/180),-exp(23),4711>`. Anything for which
`vlength(V)` doesn't return zero. (Presuming, of couse, that your mesh
is properly closed. Otherwise, the best choice in your case is whatever
direction is considered to be "up" with respect to the mesh.)


> And in case there are gaps, is there any program that can close any open
> gaps in meshes, POV, obj, 3DS, whatever format?

I'm pretty sure meshlab is able to do that. Blender also surely provides
a way, though it might take you on a sightseeing trip through the entire
software. For very small gaps where the vertices of adjacent triangles
just don't meet up exactly, PoseRay also provides a tool.

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