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