Hybrid hatching-shading method for depicting of relief in modern maps

1
Hybrid hatching-shading method for depicting of
relief in modern maps

• Marjan Sikora
• Faculty of Electrical Engineering, Mechanical
  Engineering and Naval Architecture
• University of Split

2
Introduction

• modern cartography not only thematic layers,
  but also relief
• most common methods
• contour mapping
• shaded relief

3
Contour mapping

• contours-lines connecting points of the same
  height
• advantages
• height differences are perceived easily
• possible correct height direction
• disadvantage
• relief is not experienced intuitively

4
Shaded relief

• areas oriented toward the source of light are
  brighter, those oriented opposite darker
• advantage
• the shape of the terrain is intuitively perceived
• disadvantage
• height cannot be determined exactly
• on darker areas (shades) other map elements
  (lines, symbols, annotations) are not readable

5
Possible solution

• recently in topographic as well as thematic maps
  those two techniques are combined
• shaded relief is faded in order not to interfere
  with other map elements

6
Alternative

• alternative is hatching method first developed by
  German major J. G. Lehmann (1765-1811)
• based on hatching the hatches are drawn
  according to the slope of the terrain

7
Hatching method

• hatches are drawn perpendicular to contour lines,
  and they vary in length and width
• the bigger the slope of the terrain, the shorter
  and thicker the hatches are

8
Hatching method

• advantages
• method enables good perception of the slope of
  the terrain
• the hatches are perpendicular to contour lines,
  and that is the direction of the flow of the
  water
• the force of the abrasion of water often creates
  the canals in the real world, so this method
  enables that the form of the terrain could be
  easily perceived

9
Hatching method

• dissadvantage
• it creates the same relief map, no matter in what
  direction the light comes
• one cannot easily perceive the orientation of the
  terrain

10
Hybrid hatching-shading method

• in order to overcome the shortcoming of hatching
  method, the combined hatching-shading method was
  developed

11
Hybrid hatching-shading method

• hatches are drawn with their midpoint on the
  contour, and their direction is perpendicular to
  the contour
• the width of hatch-lines doesnt depend on the
  slope of the terrain instead it depends on the
  orientation of the terrain, as with shaded-relief
  map

12
Algorithm

• for all contour lines do following
• draw hatch line on the beginning of the contour
  perpendicular to the contour
• set the width of the line according to the
  formula (angleDifference is the difference
  between the angle of the light and the angle of
  the hatch line)
• lineWidthminWidthangleDifference(maxWidth-minWi
  dth)
• move along the contour in the clockwise direction
  for the specified distance
• repeat the steps 1-3 until the end of the contour
  is reached

13
Algorithm

• the program was coded in VBA (Visual Basic for
  Applications) lanaguage for AutoCAD 2006

14
Advantages

• advantages
• since the hatches are drawn in the place of
  contours, the height of terrain can be accurately
  determined
• the direction of hatch-lines shows the direction
  of the water flow lines
• the width of hatch lines gives the impression of
  shading, and depicts the orientation of the
  relief.

15
Dissadvantages

• the length of the hatches is same no matter what
  the slope of terrain is
• in the place of the bigger slope, the overlap of
  the hatches occur
• in the place of the flatter terrain the hatch
  contours are too distant
• possible solution draw hatches variable length
  from contour to contour
• the algorithm has a problem with the partial
  contour lines ones that are not closed
• present algorithm cannot always correctly
  determine the orientation toward the light source
• possible solution user interaction

16
Comparison
17
Conclusion

• the hybrid hatching-shading method can be an
  interesting alternative to present methods
• it is aesthetically attractive, and analytically
  correct and informative
• further development of the algorithm would solve
  some shortcomings in the algorithm