Hybrid hatching-shading method for depicting of relief in modern maps
Marjan SikoraFaculty of Electrical Engineering, Mechanical Engineering and Naval
ArchitectureUniversity of Split
Introduction modern
cartography – not only thematic layers, but also relief
most common methods: contour mapping shaded relief
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
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
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
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
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
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
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
Hybrid hatching-shading method in order to
overcome the shortcoming of hatching method, the combined hatching-shading method was developed
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 doesn’t depend on the slope of the terrain – instead it depends on the orientation of the terrain, as with shaded-relief map
Algorithm for all contour lines do following:
1. draw hatch line on the beginning of the contour perpendicular to the contour
2. 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):
1. lineWidth=minWidth+angleDifference*(maxWidth-minWidth)
3. move along the contour in the clockwise direction for the specified distance
4. repeat the steps 1-3 until the end of the contour is reached
Algorithm the program was
coded in VBA (Visual Basic for Applications) lanaguage for AutoCAD 2006
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.
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
Comparison
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