Tenta 090114 Flashcards
Describe the different components of the Bézier formula and what they are used for!
- Pi: control points, defines the curve
- Bin: weight functions, defines how the different controlpoints affect the curve
- n: Order of the curve
- n+1: number of control points
There is an error on the slide so also=n-1 and number of points=n is OK.
Name two types of curves used in geometry modeling
- Bézier
- B-spline
are two types of curves used in geometry modeling.
What is the advantage of B-spline curves compared to Bézier?
- better local control of the curve
- order of polynomial does not increase with the number of control points
- easier to define joined curve segments
Describe how trimmed parametric surfaces are defined/created
- Parametric surfaces are defined in a similar way as parametric curves but with two parameters u and v
- Parametric curves are defined in the same 2D parametric space
- -> they are used to create holes
- -> or outer boundary of the surface
- The trimmed parametric surface is transformed to 3D space.
Describe how variation analysis works and what they are used for!
Variation analysis with (Monte Carlo simulation)
- calculates a statistical prediction of the variation in critical measures
- Statistical method - random data
- Tolerances on parts are randomly generated within defined distributions, tolerances and Cp
- Distributions for critical measures are generated from thousands of iterations
- All kinematical relations and sensitives are captured in 3D assembly model
Describe how contribution analysis works and what they are used for!
- calculates a ranked list of how all input tolerances contributes to the variation in the critical measures
- All input parameters are varied wit-hin their tolerances on 3 levels
- Max output is registered
- Contribution is calculated in percent as % contribution=100*delta(output)/sum(delta(output))
Describe how stability analysis works and what they are used for!
- can be used to analyze the influence of each part locating scheme on
- -> variation amplification, color coding
- -> position stability
- -> critical product dimensions - It is done by disturbing each locating point with a unit disturbance
- and summarizing their contribution with RSS
Computer graphics and virtual reality
Name two different methods for advanced 3D computer graphics rendering
- Ray-Tracing
2. Radiosity
Describe how Ray-Tracing works and advantages and disadvantages ´the method
DESCRIPTION:
- Follow light rays from the observer, one for each pixel
- Calculate how the ray is mirrored and reflected when it hits surfaces in the model, and save the way in a tree graph
- Calculate the intensity at the initial points with illumination models
- use the tree to calculate the intensities at each pixel
- handles automatically shadows , hidden surfaces and clipping
ADVANTAGE:
- good at transparent objects
- handles specular reflection well
- good at point reflection
DISADVANTAGE:
- unnaturally sharp shadows
- bad at diffuse reflection
- not good at global light sources
- slow
Describe how Radiosity works and advantages and disadvantages the method
DESCRIPTION:
- Based on the effect that light sources and surfaces are emitting light
- is done by iterating the emission of light
- In the first step only surfaces with direct light are visible
- In the next step these surfaces emits light to other surfaces
- This is repeated until the result is satisfactory
ADVANTAGE:
- Good at diffuse reflection
- Gives realistic shadows
- Good at global light sources
DISADVANTAGE:
- Not good at specular reflection
- Not good for transparent objects
- Not good at point light sources
- slow
Describe how so called shutter glasses can be used to obtain stereo projection on an ordinary computer screen
- Gives 3D by “blocking” one eye at the time
- This is synchronized with the computer which alternates between views for the left and right eye respectively
- The view are calculated with perspective projection
- The view for the left eye is calculated by moving the picture half the distance of the eyes to the left
- For the right eye the picture is moved the same distance to the right
Describe some problems related to using the CAD-system within a number of different functions
- Different functions uses different software requiring different file formats: problem with file conversion
- Problem with access to the right models
describe the concepts of component based and feature based assembly modeling
COMPONENT BASED ASSEMBY MODELING:
- The position of the part in the assembly is determined by specifying its position and orientation in global or relative coordinates
FEATURE BASED ASSEMBLY MODELING:
- Associates form features on different parts
- handles restrictions on form, position, orientation etc. between mating form features
Describe three types of solid models
- Decomposition models
- Constructive models
- Boundary representation
Describe decomposition models together with advantages and disadvantages
- Decomposition models can be made of voxels or be cellbased. (voxels is when the solid is composed of a number of cubes and cellbased is when the solid is built up by polygons.)
DISADVANTAGE:
- Is an approximate model and requires a lot of memory for high precision
ADVANTAGE
- Is suitable for different types of calculation
