[GRASS-dev] GSOC Horizons and Stratigraphy

Benjamin Ducke benducke at fastmail.fm
Tue Jun 25 01:44:54 PDT 2013

On 06/25/2013 10:21 AM, Sören Gebbert wrote:
> Hi Tim,
> i am the second mentor in your SoC project, and will try to help you
> with the 3D raster approach in GRASS.
> The 3D raster implementation in GRASS is using a tiled based storage
> approach.[1]
> The tiles can be stored in compressed form (zlib in GRASS7) or
> uncompressed form on the hard disk. Usually you store them in compressed
> form. Hence in case you have many tiles that are empty or have equal
> data, the compression is very high. GRASS can handle 3D raster maps up
> to hundreds of GB in size. I tested 3D raster maps with about 12 GB in
> size. The main memory is not an issue when processing 3D raster maps,
> since only a limited number of tiles is read into main memory at
> runtime. You can specify the tile size of each 3D raster map that you
> create. Hence you can adjust it to the needs of the soil depths resolution.
> In addition you can specify a 3D raster mask that works pretty the same
> way as masks in the raster approach in GRASS.

Simply great! Even after having used GRASS for such a long
time, I keep being amazed by its capabilities.

> Please don't bother to ask, if you have any questions about the 3D
> raster implementation.

That should read: "Please don't hesitate to ask" -- I am sure ;)



> Best regards
> Soeren
> [1] http://grass.osgeo.org/programming7/raster3dlib.html
> 2013/6/25 Tim Bailey <timibly at gmail.com <mailto:timibly at gmail.com>>
>     Hi Ben,
>     All that I meant by mask is, in this case,  an r3 map that defines a
>     subset of space that subsequent operations are constrained to. I
>     guess I was just expressing worry about creating runaway data
>     demands.The region settings act as a three dimensional bounding
>     cube, does not seem adequate to constrain a tiling scheme with
>     relatively sparse data.In the compromise scenario that Dylan
>     suggested with 10 meter xy and 1 cm z resolution and 1 meter depth
>     we would be looking at populating 10000 voxels per hectare for a
>     flat landscape. However if we were using a simple bounding box to
>     define the region and we had 5 meters of relief we would end up with
>     50000 or 60000 voxels. As the area of coverage gets bigger cost of
>     the range in z values gets worse.
>     Tim
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Dr. Benjamin Ducke, M.A.
{*} Geospatial Consultant
{*} GIS Developer

   benducke at fastmail.fm

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