Skip to main content
  • EN

Hi there,

One of my customers has a very large raster DTM (spacing 1 meter over a large region) that comes from numerous tiles.

He wants to compute consistent contours over the whole dataset, and ContourGenerator should be OK for this, but...

Computing contours on tiles independently causes issues on tiles boundaries (impossible to combine the contours that do not fit over tile boundaries.

Computing contours on the whole mosaic fails after around 1 hour.

Any thoughts about a clever method ?

Also, I wanted to check more about the surface model used internally by the SurfaceModeller, to see if it could help build a surface model incrementally, but did not find much documentation on using this option.

Thanks for your help,

Fred

You could process them in tiles and then combine the tiles afterwards, if you use a Snapper, grouping by contour value, you should be able to get rid of the seams.

Another thing worth trying is processing them in tiles that *slightly* overlap and then snap the resulting lines.

You could process them in tiles and then combine the tiles afterwards, if you use a Snapper, grouping by contour value, you should be able to get rid of the seams.

Another thing worth trying is processing them in tiles that *slightly* overlap and then snap the resulting lines.

Hi Hans,

Thanks for the answer. I was pretty sure you'd be ready to give advice on this one :)

Actually, processing in tiles strictly does not produce very nice results.

I was considering building slightly overlapping tiles as you mentioned, but was hoping for some hands-on experience regarding the overlap ratio to be honest :)

So, my remaining question here would be : should we use a large overlap to promote consistency between contours over tiles and clip to tile extent, or should we use a minimal overlap and just snap contour lines between tiles...

Anyone bumped into the same issue and found which is the best (or another clever trick we would not have thought of) ?

Cheers,

Fred

I second the recommendation to create tiles with an overlap, then clip the contours to the original tile size and snap (end point) the clipped lines only. You don't want the snapper affecting the contours other than along the edges.

 

 

You may want to experiment with the size of the input and the ram, it may be more efficient to process 4 or 9 of the original tiles in one run.

 

 

I've never incrementally processed terrain this way, but I would expect 10 to 20 pixels of overlap to be sufficient to avoid most edge effects.

Reply


Community Stats

30,190
Posts
114,593
Replies
37,854
Members
Terms & ConditionsCookie settings
A product of
Safe Software respectfully acknowledges that we live, learn and work on the traditional and unceded territories of the Kwantlen, Katzie, and Semiahmoo First Nations.