Computer Graphics

Two File Types: Vector & Raster

end Vector direction length angle midpoint etc… start

Vectors: Creates easily defined and manipulated objects, like lines, curves, boxes, cylinders, etc… Vector data can be in 2D or 3D. Vector files are relatively small in size.

Problem: Not all information is based on objects. (i.e. photographs and paintings) No real practical way to experience vector data. (i.e. monitors and printers use a grid of dots or pixels.)

Raster

Raster: Made up of square Pixels (Picture Elements). Best when used to represent pictures or images. Raster data is very portable with common, device independent formats (i.e. computer, camera, etc…). Pixels are easily viewed on a monitor or printed on paper.

Problem: Not all information is based on images. (i.e. lines, curves, boxes, cylinders, etc…) Difficult to modify. Limited to 2D. File sizes can be very large.

OK, So let’s make a wall

Pixels (raster)?

or Geometry (vector)?

How about a brick wall?

Geometry?

or Pixels?

Geometry: Pros: Fully three-dimensional Casts shadows, reflections, etc… Easier to position and modify Cons: Takes more time to calculate (render) - Slow Complex textures hard to model

Pixels: Pros: Takes less time to calculate (render) – Fast Easily represents complex textures Cons: Can be difficult to accurately position Modification requires different software Usually requires external files (texture maps)

Modeling

Modeling Build Scan/Digitize Procedural

Build: Creating objects, surfaces, edges, etc… from scratch.

Scan/Digitize: Scan – Surfaces created by optical or laser scanner.

Procedural: Geometry created by user defined equations. Typically used for large “random” scenes (crowds, cityscapes, environmental systems, etc…)

Types of Models

Parametric & Surface

Geometry defined by parameters. Parametric Geometry defined by parameters.

Surfaces defined by 3 sided geometry (Triangles) Surface: Mesh Surfaces defined by 3 sided geometry (Triangles)

Surfaces defined by Curves and Control Points Surface: NURBS Surfaces defined by Curves and Control Points

Surfaces defined by 4 sided geometry (Rectangles) Surface: Polygon Surfaces defined by 4 sided geometry (Rectangles)

Output

Output - Still: Single raster (pixels) image. Common formats – JPEG/JPG, TIFF/TIF, etc… Compression reduces file size (and with JPG, quality).

Output - Still: Usually scrutinized – More detail is required.

Output - Still: Large images need lots of Pixels, resulting in long render times (above image over 1 hour for 3000x2000 pixels).

Output - Animation: Sequential raster (pixels) images. Common formats: MPEG (generic) AVI, WMV (windows) MOV (apple)

Output - Animation: Compression (CoDec) critical to manage file size. Above sequence: compressed (~20-60MB) uncompressed (1.5GB)

Output - Animation: Individual frames less scrutinized, allowing less detail.

Output - Animation: Smaller images require fewer pixels, thus shorter rendering times per frame than stills (above image 10 minutes per frame). BUT,….

Output - Animation: Long animations require many frames (above animation has 2000 frames).

Output - Animation: At 10 minutes a frame, entire animation requires 20,000 minutes to complete (about 14 machine days).

Output - Video Games: Action and interactivity demands immediate or real-time rendering, which requires dedicated rendering and video hardware.

Output - Video Games: To lower rendering times, game designers use “low polygon modeling” and extensive texture mapping. Simple geometry + pixels = fast rendering times.

Subtractive or Additive Output – 3D Printer: Subtractive or Additive

Output – 3D Printer: Solid or Liquid Media

Output – 3D Printer: Stratasys 1200es. ABS (chemical media) STL (stereolithography) file