Help with 3D

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Raster 2.5D Surface

This is the "typical" case, and most GRASS r.* modules work in this mode. The GIS layer is defined by north,south,east,west and the raster map's cell values represent the elevation.

Snippet from the Wikipedia definition: "The idea is that the program's canvas represents a normal 2D painting surface, but that the data structure that holds the pixel information is also able to store information regarding z-index (depth) as well as other information such as material settings, specularity, etc. With this data it is thus possible to simulate lighting, shadows, and so on."

Horizontal (2D) region settings are handled by the g.region module. The third dimension is unbound.

2.5D rasters may be visualized in 3D with GRASS's NVIZ program, or as a shaded relief in 2D space with the r.shaded.relief module.

Screenshots

Example

(spearfish dataset)

g.region rast=elevation.10m
nviz elev=elevation.10m

Raster 3D Volumes (voxels)

Support for 3D rasters (voxels) is relatively new in GRASS and is primarily handled by the r3.* modules. A 3D raster can be thought of as a stack of 2D raster maps forming a 3D cube of data cells.

Region settings

Region settings are handled by the g.region module. Special 3D raster controls for g.region include:

-3 flag:  Prints 3D settings
      t   Value for the top edge
      b   Value for the bottom edge
   res3   3D grid resolution (north-south, east-west and top-bottom)
  tbres   Top-bottom grid resolution 3D

and

 rast3d   Set region to match this 3D raster map (both 2D and 3D values)

(??) 3dview Set region to match this 3dview file


Examples

  • Custom volume creation. Here is a small Octave (Matlab) script to create a text file suitable for loading as a 3D raster with r3.in.ascii.
    • Here is the file that this script creates:

vox_data50.txt.gz

x= y= z= 50;

cd ~/grass/
fp = fopen('vox_data50.txt', 'wt')

fprintf(fp, 'north: %d\n', y);
fprintf(fp, 'south: 0\n');
fprintf(fp, 'east: %d\n', x);
fprintf(fp, 'west: 0\n');
fprintf(fp, 'top: %d\n', z);
fprintf(fp, 'bottom: 0\n');
fprintf(fp, 'rows: %d\n', y);
fprintf(fp, 'cols: %d\n', x);
fprintf(fp, 'levels: %d\n', z);

for dep = 1:z
  for row = 1:y
    for col = 1:x
       fprintf(fp, '%.4f', col + (row^2 /2) + dep^2 );
       if(col < 50)
          fprintf(fp, ' ');
       end
    end
    fprintf(fp, '\n');
  end
  disp(['dep ' num2str(dep)])
  fflush(stdout);
end
fclose(fp)

Vector 3D point data

  • v.in.ascii -z format=point
  • r.in.xyz

Screenshot

3D points defining the hull of a ship, visualized using NVIZ

Example

TODO: import star guide and display using NVIZ

Vector 3D polygons

intro

    • faces
    • kernel
  • GRASS ascii format definition
  • "v.in.ascii -z"
  • Visualization with NVIZ: must be placed on a raster surface or constant surface. It may be useful to set the transparency attribute of the raster surface to something unobtrusive.

Screenshots


Example

pyramid: the following is an example of 3D vector surfaces in GRASS standard ascii format. load with v.in.ascii.

# 3D Pyramid in GRASS:  (kernel currently unused?)
#  v.in.ascii in=pyramid.vasc out=pyramid_3d format=standard -nz
#  g.region n=150 s=-50 w=-50 e=150 res=10
#  r.mapcalc one=1
#  nviz elev=one vect=pyramid_3d
#
#  tip: in nviz try setting the raster surface transparency to 50%
#
F 5
 0 0 10
 0 100 10
 100 100 10
 100 0 10
 0 0 10
F 4
 0 0 10
 50 50 80
 100 0 10
 0 0 10
F 4
 0 100 10
 50 50 80
 0 0 10
 0 100 10
F 4
 100 100 10
 50 50 80
 0 100 10
 100 100 10
F 4
 100 0 10
 50 50 80
 100 100 10
 100 0 10
K 1 1
 40 50 40
 1 1

Visualization Tools

  • output to VTK
  • output to POVray
  • output to V5D