[GRASS-user] 3D volume interpolation help

[Markus Neteler]

On Wed, Mar 31, 2010 at 8:26 PM, Carlos Grohmann
<carlos.grohmann at gmail.com> wrote:
> Hi all, it's been a while :)
>
> I have a student who needs to create volumes from a 3D points file.
> The ASCII file looks like this:
>
> 741665|7187390|205.67|96|1|1|2|100|0|90
> 741736.92|7187280.39|193.89|90|2|1|2|92|0|90
> 741736.92|7187280.39|193.39|50|2|1|2|58|0|90
> 741665|7187390|191.03|96|1|1|2|100|0|90
> 741681|7187270|190.85|94|1|1|2|100|0|90
>
> there are 181 entries, which correspond to drill core samples, so
> actually we have 9 cores (same XY, different Z)
>
> importing as a 3D vector works fine
> v.in.ascii -z input=/home/guano/RQD_2.csv output=rqd_drill z=3
>
> now set up the region:
>  g.region t=210 b=125 tbres=1 res3=1 -p3

Note: I have used (in NC location, since I don't have yours):
g.region t=210 b=125 tbres=1 res3=1 -p3 vect=rqd_drill res=1 -a

> projection: 1 (UTM)
> zone:       21
> datum:      ** unknown (default: WGS84) **
> ellipsoid:  sam69
> north:      7187390
> south:      7187270
> west:       741665
> east:       741761
> top:        210.00000000
> bottom:     125.00000000
> nsres:      1
> nsres3:     1
> ewres:      1
> ewres3:     1
> tbres:      1
> rows:       120
> rows3:      120
> cols:       96
> cols3:      96
> depths:     85
> cells:      11520
> 3dcells:    979200

I have different cols and rows but that may be ok for a test.

v.db.select rqd_drill column=int_1
int_1
96
90
50
96
94


> OK, now on to interpolation (int_1 is the 4th col):
>
>  v.vol.rst --overwrite input=RQD_2 wcolumn=int_1 segmax=10 npmin=10
> dmin=0.05 elev=teste3d

warning: above the file name was rqd_drill.

> 181 records selected from table
> WARNING: strip exists with insufficient data
> Processing all selected output files will require 46080 bytes of disk space
> for temp files
...
> OK, let's see what happened:
>  r3.info teste3d
...
>  |            N:    7187390    S:    7187270   Res:     1                     |
>  |            E:     741761    W:     741665   Res:     1                     |
>  |            T:        210    B:        125   Res:     1                     |
>  |   Range of data:   min =         98 max =         98                       |


I get:

r3.info teste3d | grep -i Range
 |   Range of data:   min = 67.83296967 max = 94.63486481                     |
...
> So, I got a map with min=max=98 (which is the mean value of that column).
>
> OK, what are we doing wrong? I got to admit I'm new to 3d interpolation.

... could it be as simple as you used the wrong input file?

I used GRASS 6.4.0RC6 here which appears to work fine.

Markus