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Large scale shading cliffs/rift

- - - - - shading rift city

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#1
Frank B.

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Hi all,

 

I've been a long time reader of the invaluable information here in this forum and I've always found my inspiration in the maps published here. But now I am struggeling with a map design issue myself and I can't find the "right" technology to achieve what I want.

 

I'm creating a map for the downtown of a city. The city has a rift which parts it more or less into two halves. Since the map aims at tourists it is quite critical to show the height differences between up (300m) and down (250m). It's not about the actual height difference but more about showing the steepness and the fact that there are substantial differences.

 

Usually I'd do this by creating a hillshade and overlay the hillshade with my data. This works fairly well for most maps above 1:20.000 or so.  But since the scale's much larger I'm struggling to create a good visual approach. I've attached a screenshot of the map as it is right now, and you can investigate further on Google Maps (try the options for the terrain). The rift has some really steep cliffs and I am out of ideas. In addition to the naturally created, steep steps there are also some remarkable elements made by men, namely the fortifications done by Vauban.

 

So in the end I am looking for ideas on how I can substitute / enhance the shading technique I am using right now. The hillshade visible in the screenshot was created by rather accurate contour lines, so they reflect to some degree the complexness of the terrain, but the algorithm used to create the hillshade/DTM frequently fails in some locations where the changes in the terrain are too harsh.

 

So I am asking what other techniques I can use to show the terrain, like maybe hachures and what your experience with these technologies is?

 

Many thank,

Frank

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#2
frax

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Hi - maybe you need a higher resolution DEM?


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#3
Hans van der Maarel

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As somebody who has walked around in Luxembourg City I can attest to the steepness you can encounter there.

 

I agree with Frax, a higher-resolution DEM would be an improvement. But then I'd also consider a more complex hillshade than just one direction lighting to cover all angles.

 

The Luxembourgisch Cadastre uses special symbology to indicate steep cliff faces, see http://g-o.lu/bzwz7 for roughly the same area at their most detailed scale. One scale level down they use a combination of hillshade and contour lines: http://g-o.lu/m5jfl


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#4
Frank B.

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Hi,

 

thanks for your answers. I fear a high-res DEM is out of the budget, but I like the idea of the more complex hillshade. I will investigate this further first. I fear that using a special symbology and/or contour lines will make the map too hard to read for the intended audience and therefore I am hesitant to use them.



#5
Dennis McClendon

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I might think about constructing (by hand if necessary) very thin hachures.  I think that will immediately call visitor attention to the feature and suggest what it is.


Dennis McClendon, Chicago CartoGraphics
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#6
Charles Syrett

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Dennis is right (again!)....hachures would work well in defining the varying character of the cliffs at this large scale. See attached scan - this is from an old historical atlas, and it shows some very skillful hachure drawing to depict the relief around Jerusalem at a large scale. It may be possible to simulate this effect by doing some vector hachuring on top of multi-angled shaded relief. Challenging project!

 

Charles Syrett
Map Graphics
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#7
Frank B.

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Hi everybody,

 

thank you for the nice inspirations. Right now I am using the contour lines to create a DEM with a higher resolution, but this may take a while to finish calculating. Now I wonder how I can try out the hachures. I've never done them myself, so I would be happy for any advise on how to create them.

 

An idea would be to use the contour lines and construct the hachures by manually placing vertical lines between the contour lines which define major changes in the terrain. Has someone done this already using GIS?

 

Frank



#8
Charles Syrett

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I recall, some years ago, that somebody created an algorithm for automatic hachuring, but I also recall not being impressed with the results. My opinion is that, by their very nature, hachures need to be hand drawn. Not sure how that would be done in a GIS though.

 

Charles Syrett
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#9
Frank B.

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Yeah, I've drawn hachures in remote sensing courses in university with stereoscopic images and those funny goggles where you have to keep your parallaxes straight to see the 3D effect. But I have neither at hand here :D

But it's friday and I'll try to use the contours to depict the terrain form and try some of the snapping options in my GIS. Maybe at the end of the day I can already post some images ...



#10
Frank B.

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Ah, by the way (and in a new post, since my last one still awaits moderation), here's an interesting link concerning automatic hachure generation: http://mike.teczno.c...s/hachures.html



#11
Hans van der Maarel

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I've tried to automagically generate hachures a few years back and only got as far as something that more or less resembles the samples shown under that link, which imho is still very far removed from properly done manual hachures. Maybe I should pick it up again...


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