1raster3dintro(1) Grass User's Manual raster3dintro(1)
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6 3D raster maps in general
7 GRASS GIS is one of the few GIS software packages with 3D raster data
8 support. Data are stored as a 3D raster with 3D cells of a given vol‐
9 ume. 3D rasters are designed to support representations of trivariate
10 continuous fields. The vertical dimension supports spatial and tempo‐
11 ral units. Hence space time 3D raster with different temporal resolu‐
12 tions can be created and processed.
13 GRASS GIS 3D raster maps use the same coordinate system as 2D raster
15 maps (row count from north to south) with an additional z dimension
16 (depth) counting from bottom to top. The upper left corner (NW) is the
17 origin. 3D rasters are stored using a tile cache based approach. This
18 allows arbitrary read and write operations in the created 3D raster.
19 The size of the tiles can be specified at import time with a given
20 import module such as r3.in.ascii or the data can be retiled using
21 r3.retile after import or creation.
22 The 3D raster map coordinate system and the internal tile layout of
23 the RASTER3D library
24 Terminology and naming
26 In GRASS GIS terminology, continuous 3D data represented by regular
27 grid or lattice is called 3D raster map. 3D raster map works in 3D in
28 the same was as (2D) raster map in 2D, so it is called the same except
29 for the additional 3D. Some literature or other software may use terms
30 such as 3D grid, 3D lattice, 3D matrix, 3D array, volume, voxel, voxel
31 model, or voxel cube. Note that terms volume and volumetric often
32 refer to measuring volume (amount) of some substance which may or may
33 not be related to 3D rasters.
34 Note that GRASS GIS uses the term 3D raster map or just 3D raster for
36 short, rather than 3D raster layer because term map emphasizes the map‐
37 ping of positions to values which is the purpose of 3D raster map (in
38 mathematics, map or mapping is close to a term function) On the other
39 hand, the term layer emphasizes overlaying or stacking up. The former
40 is not the only operation done with data and the latter could be con‐
41 fusing in case of 3D raster data.
42 3D raster map is divided into cells in the same way as the (2D) raster
44 map. A cell is a cube or a (rectangular) cuboid depending on the reso‐
45 lution. The resolution influences volume of one cell. Some literature
46 or other software may use terms such as volume, volume unit, volumetric
47 pixel, volume pixel, or voxel. Note that voxel can be sometimes used
48 to refer to a whole 3D raster and that for example in 3D computer
49 graphics, voxel can denote object with some complicated shape.
50 Type of map and element name in GRASS GIS is called raster_3d. The
52 module family prefix is r3. Occasionally, 3D raster related things can
53 be referred differently, for example according to a programming lan‐
54 guage standards. This might be the case of some functions or classes
55 in Python.
56 In GRASS GIS 3D rasters as stored in tiles which are hidden from user
58 most of the time. When analyzing or visualizing 3D rasters user can
59 create slices or cross sections. Slices can be horizontal, vertical, or
60 general plains going through a 3D raster. Slices, especially the hori‐
61 zontal ones, may be called layers in some literature or some other
62 software. Cross sections are general functions, e.g. defined by 2D
63 raster, going through a 3D raster. Another often used term is an isos‐
64 uface which has the same relation to 3D raster as contour (isoline) to
65 a 2D raster. An isosurface is a surface that represent places with a
66 constant value.
67 When 3D raster is used in the way that vertical dimension represents
69 time 3D raster can be referred to as space time cubes (STC) or space
70 time cube 3D raster. Some literature may also use space time voxel
71 cube, space time voxel model or some other combination.
72 3D raster import
74 Import from external files
75 The modules r3.in.ascii and r3.in.bin supports generic x,y,z ASCII and
76 binary array import.
77 In case of CSV tables, the modules v.in.ascii (using the -z flag) may
79 be a choice to first import the 3D points as vector points and the con‐
80 vert them to 3D raster (see below).
81 Import of 3D (LiDAR) points and their statistics can be done using
83 r3.in.lidar for LiDAR data and r3.in.xyz for CSV and other ASCII text
84 formats.
85 Conversion from 3D vector points
87 3D rasters can be generated from 3D point vector data (v.to.rast3).
88 Always the full map is imported.
89 Conversion from 2D raster maps
91 3D raster can also be created based on 2D elevation map(s) and value
92 raster map(s) (r.to.rast3elev). Alternatively, a 3D raster can be com‐
93 posed of several 2D raster maps (stack of maps). 2D rasters are con‐
94 sidered as slices in this case and merged into one 3D raster map
95 (r.to.rast3).
96 3D region settings and 3D MASK
98 GRASS GIS 3D raster map processing is always performed in the current
99 3D region settings (see g.region, -p3 flags), i.e. the current region
100 extent, vertical extent and current 3D resolution are used. If the 3D
101 resolution differs from that of the input raster map(s), on-the-fly
102 resampling is performed (nearest neighbor resampling). If this is not
103 desired, the input map(s) has/have to be reinterpolated beforehand with
104 one of the dedicated modules. Masks can be set (r3.mask).
105 3D raster analyses and operations
107 Powerful 3D raster map algebra is implemented in r3.mapcalc. A 3D
108 groundwater flow model is implemented in r3.gwflow.
109 3D raster conversion to vector or 2D raster maps
111 Slices from a 3D raster map can be converted to a 2D raster map
112 (r3.to.rast). Cross sectional 2D raster map can be extracted from 3D
113 raster map based on a 2D elevation map (r3.cross.rast).
114 3D raster statistics
116 3D raster statistics can be calculated with r3.stats and r3.univar.
117 3D raster interpolation
119 From 3D vector points, GRASS 3D raster maps can be interpolated
120 (v.vol.rst). Results are 3D raster maps, however 2D raster maps can be
121 also extracted.
122 3D raster export
124 The modules r3.out.ascii and r3.out.bin support the export of 3D raster
125 maps as ASCII or binary files. The output of these modules can be
126 imported with the corresponding import modules noted above.
127 NetCDF export of 3D raster maps can be performed using the module
129 r3.out.netcdf. It supports 3D raster maps with spatial dimensions and
130 temporal (vertical) dimension.
131 Working with 3D visualization software
133 GRASS GIS can be used for visualization of 3D rasters, however it has
134 also tools to easily export the data into other visualization packages.
135 GRASS GIS 3D raster maps can be exported to VTK using r3.out.vtk. VTK
137 files can be visualized with the VTK Toolkit, Paraview and MayaVi.
138 Moreover, GRASS GIS 2D raster maps can be exported to VTK with
139 r.out.vtk and GRASS GIS vector maps can be exported to VTK with
140 v.out.vtk.
141 Alternatively, GRASS 3D raster maps can be imported and exported
143 from/to Vis5D (r3.in.v5d, r3.out.v5d).
144 3D raster data types
146 3D raster’s single-precision data type is most often called "FCELL" or
147 "float", and the double-precision one "DCELL" or "double".
148 See also
150 · Introduction into raster data processing
151 · Introduction into vector data processing
153 · Introduction into image processing
155 · Introduction into temporal data processing
157 · Projections and spatial transformations
159 · wxGUI 3D View Mode
161 · m.nviz.image
163
165 Available at: 3D raster data in GRASS GIS source code (history)
166 Main index | 3D raster index | Topics index | Keywords index | Graphi‐
168 cal index | Full index
169 © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual
171GRASS 7.6.0 raster3dintro(1)