silly questions: what does refraction and what is object instancing?
cosmo71
Posts: 3,609
hello,
I have two silly questions,
1. what does refraction for what is it good?
2. What is object instancing?
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Refraction is the change in direction of a wave due to a change in its transmission medium, or to put it another way Refraction is the bending of light as it passes from one medium into another.
Most often used with Glass or water,
Instancing:- as regards the 3d program geometry instancing is the practice of rendering multiple copies of the same mesh in a scene at once. This technique is primarily used for objects such as trees, grass, or buildings which can be represented as repeated geometry without appearing unduly repetitive, but may also be used for characters.
ahhha, thank you :)
ahhha, thank you :)
As regards to instancing...a pointer is stored in scene file and the geometry is generated on an as need basis, for rendering, thereby decreasing the resources needed to render the scene.
To add to Chohole's definition, refraction is why when you have a glass of water and you stick a pencil into it, the pencil appears to break / bend.
FWIW, Reflection/Refraction/Transmission are the next topics I have in mind for my discussion of 3D surfaces on my blog. :)
To add to the foregoing, refraction (along with reflection) is what makes water in a scene look like water instead of cloudy air. Be sure to use realistic values (water's real index of refraction is 1.33 and most glass is 1.5 something). Yes, this adds a LOT of render time, but it sure makes a big difference in the look of water and glass.
More indices: http://en.wikipedia.org/wiki/List_of_refractive_indices
Many solid surfaces like Steel and Gold for example have IOR's too though it isn't that noticeable in reality.
Greetings,
Just for fun, an...instance of refraction.
That is, 5 instances of SPEX (plus the original), each with a high refractive index on the lenses.
As an interesting note, it looks like the pair in the back, which is facing away, is not refracting correctly, so it may be a 'normal' thing.
-- Morgan
[Edit: Again, just because it's fun and distracting, I added an example run through Luxus and LuxRender.]
If the lenses are single-sided, then yes, it is a 'normal' thing.
A really nice IOR list...
http://www.pixelandpoly.com/ior.html
And, the IOR for metals is more important, visually than you'd think...the nk data files that can be used by Luxrender are a series of IOR values at specific frequencies over the spectrum...and the relationship between reflection/refraction covers the entire electro-magnetic spectrum.
Technically, indices of refraction should be between two different types of material. So if you have a glass of water, there should be one index for the air to the glass, and another for the glass to the water (and another for the water to the glass on the other side and another for the glass to the air). One of the primary issues we typically have in trying to create realistic looking lenses, glasses, etc. is that our glass is "one-sided". It's a single plane surface. Which isn't physically correct.
thank you all very much :)
to the "broken pencil" in the water. If I took the pencil in the water I have to fix the values for refraction of the pencil or the refraction of the water?
The water...it should be 1.33
And if it's a glass of water, you'll need to set the IOR for the glass, too....1.52 or so would be a good value for an ordinary water tumbler.
The water (and/or the glass, depending on how your model is made) needs the refraction applied.
okay, just for understanding, it would also work if I just use other values for strength and index also without any map applied?
Yes, but air has a value of nearly 1..so unless the app uses more precise (more decimal places than 3 or 4), then you can pretty much eliminate the calculations needed for the air side of the exchange.
Another thing to remember...at least in 3Delight...refraction is going to count for raytrace bounces...so if you have a correctly modeled glass/lens and don't have enough bounces, you aren't going to get proper refraction, either. In your example, you'd need at least 4 bounces...preferably 6...
The first image has Ray Trace Depth set to 2. The second image, it is set to 8.
I have to primitive planes one behind the other and have changed values of refraction strength and index (different tries) but I allways get massive grey while opacity is at 10% for both
I drove myself nuts on this subject a while back. Silly me, I was trying to render a gal holding a glass of Champagne. I ended up having to insert clear primitive shapes inside the "liquid" in order to get the refraction through the liquid. Yes, I had to turn raytrace bounces up to 6 or 8. 15 hrs later, I had a decent looking Champagne glass. :red: At one point, I updated the image, and broke part of the refraction setup. The image is here. Note the lower part of the liquid in the glass. It looks cloudy because there is one shape inside another shape (a stretched sphere around a cone) and the sphere wasn't set properly. Note the upper part of the glass where it really looks like her dress is on the opposite side it actually is. The "liquid" prop the glass came with would not refract no matter what I did because it was a hollow shell, not a solid. The Daz primitives are modeled as proper solids.
After this render, I swore off Champagne. My characters can drink murky liquids for all I care! :lol:
I get results other than pale grey but I think that it looks not real, I do not get the result like in the second image above
I looked through this thread and didn't see any mention of this...there is one other requirement to make glass/refractive materials. That is a 'complete' environment...at least a floor and a couple of walls. Without boundaries, strange things happen. Skydomes/world balls and nearly/totally enclosed interiors work best.
Very true. I always forget to mention this because I sort of take it for granted now (my own water product includes a skyball).
Totally enclosed interiors can cause issues with some lights that Skydomes and worldballs and FlipMode's skyboxes do not cause, in my experience (I don't know why but I think comparative size of the enclosing object may matter). I almost never render in a room without one or more walls off.
Very true. I always forget to mention this because I sort of take it for granted now (my own water product includes a skyball).
Totally enclosed interiors can cause issues with some lights that Skydomes and worldballs and FlipMode's skyboxes do not cause, in my experience (I don't know why but I think comparative size of the enclosing object may matter). I almost never render in a room without one or more walls off.
I allways render inside a room with all walls on because of realism.
I just render an image with these effect and I think I got it and that I am on the way of success :) will post it then
I got it :)
Alright now where would I find this in my programs menu, which pane lets me put for example, multiple motorcycles for my race in a scene.. how would I go about using this function in DS4.6?
I can tell you how to use it in Bryce, if that's any help. I don't actually use DS.
If you look at some of the Howie Faukes sets in the store, he uses instancing to set up his scenes, for the vegetation in those. That of course is Carrara.
How ever I would imagine that there is not a lot of difference between Bryce Instances and DS one in one part, each instance is a copy of the object or group that you are using as the root of the instancing, hence why it is more often used for vegetation and architecture rather than for characters.
In Bryce you can alter the sizing of the instances, and give a range of the sizes, and dial in a degree of rotation as well, to avoid too much obvious repetition.
However, as I said I don't use DS, so am not at all sure how it works in DS.
Greetings,
In the menu, under Create, there is 'Object Instances', and you can select how many instances to create.
The important thing to understand, however, is that all the instances will have the exact same structure and surfaces as the source instance. So you can create 20 motorcycles, but they will all have the same color, and the same number (if you have a number on them). They can be posed at different angles, but not morphed differently.
If you instance a person, and then move their arm up in the air, ALL the instances will move their arms up in the air identically.
If you color them blue, they will all become blue.
But that limitation is not that large for most folks. Send In The Clones helps, as it lets you have a few more variations per instance, but I don't know how it works as it's a plugin that I don't have.
-- Morgan
Interesting, so it is not all that different to what I use.
Do tell me, do you have to one model at a time when instancing in DS, or can you actually make an instancing brush and add several different models to it to create your instances, This feature is very useful when creating forests, for example, you can have say 6 different species in the brush and dial what percentage of each you want to appear.
Very true. I always forget to mention this because I sort of take it for granted now (my own water product includes a skyball).
Totally enclosed interiors can cause issues with some lights that Skydomes and worldballs and FlipMode's skyboxes do not cause, in my experience (I don't know why but I think comparative size of the enclosing object may matter). I almost never render in a room without one or more walls off.
Some of the early refraction tests I did before doing that Champagne glass were just a cylinder primitive in front of a plane primitive. The plane had an image texture applied so I could see the refraction through the cylinder. No room needed. I don't even think I used any real lights, just the Daz Studio "headlight" behind the camera. The Champagne glass scene was in the Modern Apartment, which has 3 sides. I'll dig up that cylinder test image. It's mildly amusing...
Some of the early refraction tests I did before doing that Champagne glass were just a cylinder primitive in front of a plane primitive. The plane had an image texture applied so I could see the refraction through the cylinder. No room needed. I don't even think I used any real lights, just the Daz Studio "headlight" behind the camera. The Champagne glass scene was in the Modern Apartment, which has 3 sides. I'll dig up that cylinder test image. It's mildly amusing...
One of the common problems with a lack of environment and refraction are 'black blobs' where the camera angle/light/object all line up to bring you the 'nothingness' that surrounds your scene. Often, that simple plane with an image on it and a pretty straight on camera angle are enough to avoid the problem...so are open sides BEHIND the camera, unless you are dealing with a highly reflective object, too.
Reflection and refraction go hand in hand.
Argh! Why did I re-render this thing! I just got done saying, "No more Champagne!" :lol:
Glass Settings (Champagne flute and plain cylinder):
Reflection 100%, IOR 1.54, Opacity 5%
Liquid props (Cone and sphere inside fake liquid prop):
Reflection 0%, IOR 1.35, Opacity 0%
Caveman prop settings:
Reflection 20%
One distant light, Shadow Map shadows.
Edit: And raytrace depth=8 (ouch).
You don't have such tool in DS but you can instanciate anything to the number you want if your Hardware is able to handle it (I got it up to 1500 genesis but the viewport was beginning to be very sluggish)
The only problem then is that you have to move each instanced object to the place you want it to be and when you have a lot that is quite time consuming. I didn't find a way to move a whole group of instanced object