|
Cartographers must pay special attention to the tone of flat areas. Gray tones in analytical shadings are usually too dark and often display disconcerting random values. Using a supplemental bright gray tone to cover these regions improves the appearance. The gray tone and the shading are combined by a weighted mean:
g’ = w · g + (1 - w) · f
where
|
g'
|
New gray tone
|
|
g
|
Initial gray tone
|
|
f
|
Gray tone for flat areas
|
|
w
|
Weight for the shading
|
The weight w can be calculated using the following formula (F. Arnet, swisstopo):
| If s > a: |
 |
|
else: w = 0 |
where
|
w
|
Weight for the shading
|
|
s
|
Slope of the point [degrees]
|
|
a
|
Maximum slope without shading [degrees]
|
|
b
|
Curvature [0..1]
|
Areas with a slope below a are fully covered by the assigned bright tone for flat areas. Parameter b determines the influence of this tone. Figure 4 illustrates the effect of the two parameters together.
As an alternative to the above function, a program may offer an interactive dialog to adjust the weight as a function of slope at a more detailed level. Additionally, the influence of the flat tone can be limited to areas below a certain elevation.
 |
|
 |
Left: With lightening tone for flat areas. Righ: Without flat area lightening.
|
|
