[GRASS-user] Contours

GRASS GRASS user
1

Hi all,

I have a large DTM (5m cell size) and it covers an area of 100,000km2. I need to create contours every 10meters in the dataset. If I tile the dataset and contour each tile, the data, the contours act funny at the edges, hence the need to process the area as one area. Is grass capable of doing this?

Thanks

···

Le gach dea ghui,

Shane Carey

2

On Mon, 18 Dec 2017, Shane Carey wrote:

I have a large DTM (5m cell size) and it covers an area of 100,000km2. I
need to create contours every 10meters in the dataset. If I tile the
dataset and contour each tile, the data, the contours act funny at the
edges, hence the need to process the area as one area. Is grass capable of
doing this?

Shane,

   Yes. As long as you have sufficient memory and drive space. You can always
set the environment variable in ~/.bash_profile:

export=GRASS_VECTOR_LOWMEM=1

which will use available memory and not crash, while running more slowly.

   If I'm wrong I'm sure we'll both read about it. :slight_smile:

HTH,

Rich

3

On Mon, Dec 18, 2017 at 6:38 PM, Rich Shepard <rshepard@appl-ecosys.com> wrote:

On Mon, 18 Dec 2017, Shane Carey wrote:

I have a large DTM (5m cell size) and it covers an area of 100,000km2. I
need to create contours every 10meters in the dataset. If I tile the
dataset and contour each tile, the data, the contours act funny at the
edges, hence the need to process the area as one area. Is grass capable of
doing this?

Shane,

  Yes. As long as you have sufficient memory and drive space. You can always
set the environment variable in ~/.bash_profile:

export=GRASS_VECTOR_LOWMEM=1

which will use available memory and not crash, while running more slowly.

  If I'm wrong I'm sure we'll both read about it. :slight_smile:

Shane: please report how it goes.

Markus

PS:
If you want a tiled approach (could probably be partially run in
parallel), then you may create tiles with overlaps, then generate the
contour lines:
https://grass.osgeo.org/grass72/manuals/r.tile.html

4

On Tue, Dec 19, 2017 at 1:29 AM, Shane Carey <careyshan@gmail.com> wrote:

Hi,

Unfortunately I could not get that to work.

Please describe what the error is... otherwise it is hard to help :slight_smile:

Markus