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#1
joost michael

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hello,

I'm quite new to this website but i was hoping somebody could give me some advice on the following problem.

Im creating a large scale map (1:15.000) from Quickbird2 imagery, vectorised rivers / roads and contourlines (20m interval) generated form srtm dted level2 data.

I generated the contourlines in ArcInfo and vectorisation was based on orthorectified imagery. The problem is that the contourlines generated from dted2 have a lower accuracy and therefore these contourlines do not allways seem to appear logically on the map.

for example. a waterway intersects the same contourline several times. and contourlines are supposed to be v shaped when intersecting a waterway, sometimes this v shape is made 100m off from the waterway.

I know my dted2 accuracy is to blame for this but does anybody know how to solve this? mabye by making use of tin's or do you have to edit the contourlines by hand? what are common practices in such situations.

Thanx in advance.

Grtz,

Joost

#2
Hans van der Maarel

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The best solution is getting better data.

I wouldn't worry too much about the v-shaped contour lines, but a river that's flowing uphill is of course not possible and you'll have to make sure that never occurs. That would involve manually editing the contour lines.
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#3
Charles Syrett

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Contours generated from DEMs almost always have this problem. The only way to correct it is through manual editing. The other possibility is to use already existing contours to generate a new grid (DEM), from which you can then generate new contours at whatever interval you want. Even then, you have to be careful what algorithm you use to create the grid. As you suggested, a TIN would help, as long as there are lots of elevation points on the drainage lines. If not, you would have to manually add breaklines.

The DEST algorithm used in Manifold is one that was developed specifically to "sense" drainage lines and to create clean "Vs" where contours cross them. I've used it, and it's better than other TIN approaches, but still far from perfect in practice. One way or the other, I don't think you can escape the need to manually edit and/or draw. :)

Charles Syrett
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#4
frax

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It was a long time since I played with things like that, but I think you should be able to use the drainage lines as you create a TIN, as sinks or something (don't know the exact terminology). It may not be correct in the end though, but it would probably look better...
Hugo Ahlenius
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#5
joost michael

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Thanks for the advise. I will centainly experiment with creating tins. Because in my case rappid map making was critical for the project, i have chosen to mask my waterways for now. But that doesnt make my map look better :D

Grtz




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