Computer graphics is the computational creation and manipulation of visual data

Importance of computer graphics

• Understanding and interpreting information - Visualization is necessary for dealing with cartographic data
• Improved communitcation with computers - Graphical and audio interfaces are helpful
• Better cartographic designs -

Computer aided design

• Architecture
• Engineering

Visualization

• Cartography
• Demographic studies
• Financial planning

Mathematical Structures

• Spaces, points, vectors; dusts, curves, surfaces, solids

Modeling

• Description of objects and their attributes, including: Primitives (e.g. pixels, polygons), Attributes (e.g. color, texture), Connectivity (e.g. scene graphs), Dynamics (e.g. motion, morphing)
• and techniques for object modeling, including: Polygon meshes, Solid Geometry, Patches

User Interfaces

• Human factors, I/O devices, color theory, workstations, interactive techniques, map design, animation

Graphics Software

• Graphics APIs; paint, draw, CAD and animation software; modeling and image databases

Graphics Hardware

• I/O devices, specialized chips, specialized architectures

Viewing

• Abstract to device coordinate transformations, the syntehetic camera, windows, viewports, clipping

Rendering

• Transparency, translucency, reflection, refraction, shadows, shading, surface and texture mapping

Image Processing

• Image description, image storage, image transformations, image filtering, image enhancement, pattern recognition, edge detection, object reconstruction

Objects (usually 3-D) are the conceptual entities that exist in their own coordinate systems

Images (usually 2-D) are the realizations of objects on some media

To make images, we need to take into account

• The position and orientation of the viewer
• The properties of the camera, such as its focal length and aspect ratio
• Properties of the materials
• How the scene is lit

Projection turns 3-D into 2-D

Input Devices

• Physical: Keyboard, mouse, tablet, touch pad, touch screen, camera, light pen, microphone, etc

Output Devices

• Examples: CRT display, LED display, LCD display, Plasma display, printer, plotter, e-paper, hologram generator, film recorder, sound recorder, speaker, etc

2-D output devices are either vector devices, which physically draw line segments (like a plotter), or raster devices, which display a grid of colored pixels (picture elements)

Make sure to take a look at screen resolutions

Frame Buffer

• Memory that holds data for each pixel. May be separate buffers: color buffer, depth buffer, stencil buffer, accumulation buffer
• Each buffer has a number of bits per pixel, called its depth

The OpenGL pipeline works roughly as follows

Geocoding is the conversion of spatial information into computer-readable form

Reasons

• geocode with a specific mapping purpose in mind
• general purpose geocoding

Levels of geocoding

• Convert the graphic elements of a map into numbers (nontopological) - e.g. river & road plotted as lines ontop of each other
• Encode important topological information about the data - e.g. river & road, bridge is added to break the river

1. Location

• An attribute of location on the earth's surface
• x & y values represent latitude & longitude

2. Data Volume

• Many cartographic data processing problems are generic problems of large data sets

3. Dimension

• Traditionally, cartography has divided data into points, lines, & areas
• Levels of measurement are divided into nominal, ordinal, interval, & ratio

4. (Dis)Continuity

• Some map types, such as contour maps, assume a continuous distribution, while others, such as choropleth maps, assume a discontinuous distribution

1. Size

• Size is characterized in measurement

2. Distribution

• Density is a measure of the distribution of a phenomenon across space

3. Pattern & Orientation

• Pattern is actually a characteristic of distributions and is a description of their structure
• Pattern can be thought of as a lack of randomness

4. Neighborhood

• eighborhood property defines how the property varies over space
• Geographic studies often examine the relationship between some geographic phenomenon and distance

5. Contiguity

• Contiguity is the property of being related by juxtaposition, i.e. by a sharing of a common boundary

6. Shape

• Shapes depicts the measures of the level of correspondence between shapes

7. Scale

• Scale is the representative fraction, the ratio of distances on a map to the same distances in that part of the world shown on the map

Minimize labor input

Detect & eliminate errors

Optimize storage efficiency

Maximize flexibility

Semiautomated digitizing

Automated digitizing

Design symbols for airport & car

Queries about this Lesson, please send them to: jmwaura@jkuat.ac.ke

*References*

• Analytical and Computer Cartography, 2nd ed. Keith C. Claike
• Geographic Information Systems: The Microcomputer and Modern Cartography, 1st ed. Fraser Taylor