[GRASS-dev] How many points in a point layer and v.surf.bspline questions

[Markus Metz]

On Mon, Jan 3, 2011 at 2:57 PM, Markus Neteler <neteler at osgeo.org> wrote:
> hi Doug,
>
> On Mon, Jan 3, 2011 at 2:26 PM,  <Doug_Newcomb at fws.gov> wrote:
>>
>> Hi Folks,
>>
>> I aggregated all of the bare earth lidar points for the state of North
>> Carolina into a single file  Imported all 8.5 billion points for NC into one
>> point layer with no topology.  I was sort of curious to see if I could
>> generate a seamless 20 ft elevation grid for the State of North Carolina
>> from a single data layerusing bspline and  tried the following command:
>>
>> GRASS 6.5.svn (ncstpft_nad83):~ > v.surf.bspline input=all_nc_be_pts2
>> raster=all_nc_be_20ft_bspline sie=40 sin=40 layer=0
>> WARNING: Coor files of vector map <all_nc_be_pts2 at statewide> is larger than
>>          it should be (158913789952 bytes excess)
>> Cells for raster map <all_nc_be_20ft_bspline> will be interpolated
>> ERROR: G_calloc: unable to allocate 18446744071812941729 * 8 bytes of
>>        memory at dalloc.c:66
>
> you are hitting the limits :) I dunno if large file support helps, but
> for vector data
> it is only available in GRASS 7 to my knowledge.
>
Large file support does not help here because 8.5 billion points
exceeds the number of supported features in GRASS vectors which is
about 2 billion (2,147,483,647 to be precise).

Further on, a region with 6.8 billion cells is a bit large since the
interpolated raster will be held in memory which would require about
50 GB RAM (that could be fixed for v.surf.bspline by keeping
intermediate data on disk). No idea where the request for
18446744071812941729 * 8 bytes comes from, this is astronomical.

Apart from that, spline steps of 40 seem ok, since the point distance
is 5 m or less, spline steps of 20 would also be ok. The larger the
spline steps, the smoother the resulting surface. Smoothing is also
controlled through lambda.

Markus M