Relif Representation

Question 1

Visual methods

Answer 1

• spot heights
• isolines (contours)
• layers contours (hypos metric layers)
• hill shading

Question 2

Spot heights

Answer 2

Limits how many points we can show. Value maybe printed at location. Very accurate for specific points. Normally has dot to indicate position

Question 3

Isolines (contours)

Answer 3

Line of equal value above datum. Normally have equal vertical interval and determine how we want to represent the slope, plus determines how much detail we can include.

Spacing of lines indicate slope closer the lines the steeper the slope. Finest line = 0.1mm. 2mm is standard, 3 is the highest.

Irregular intervals sometimes used is there is a skewed data set. This is harder to interpret. Best avoided

Question 4

Supplementary contours

Answer 4

Used when contour interval is too large. Fine line or dashed

Question 5

Three types of contours

Answer 5

• index
• supplementary
• numbered

Question 6

Improving visualisation

Answer 6

Certain key contours are made thicker. No difference in colour. 50, 100, 150 ect are normally made thicker but depends on interval and go in nice round steps. This make it easier for the user as the can see the information standing out. Should read correctly up slope.

Question 7

Contour legibility

Answer 7

Contours must never touch so sometimes get broken when computer generated. Top and bottom slope maintained

Question 8

Layers colours/ hypos metric layers

Answer 8

Colour area between two contours - relatively small number of slopes. May blend colours but there has to be a clear distinction so users can see patterns

Question 9

Surface hill shading

Answer 9

Based on the concept of light reflected from surface. The more light reaching a surface = lighter. Therefore less light reaching the surface is darker. DOESNT INVOLVE SHADOWS. Light source generally assumed to be above and to the NorthWest. Gives best perceptual impression

Question 10

Shading models

Answer 10

The simplest model = verticals illum
The steeper the slope the greater the shading = darkest. Horizontal = white. This is to convey the impression of a slope. Shading models are very abstract.

Question 11

Analytical hill shading

Answer 11

Position of light source can help us create a grey scale. Compute slope and aspect of facet.

Digital doesn’t have the flexibility of manual shading. Can combine 2 or 3 shadings with different parameters and weighing a. Can get a sharper impression when it is done manually. Has improve tremendously more recently