1raster3dintro(1)              Grass User's Manual             raster3dintro(1)
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3D raster data in GRASS GIS

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.
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14       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
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25   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.
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35       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.
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43       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.
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51       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.
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57       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.
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68       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.
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73   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.
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78       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).
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82       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.
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86   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.
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90   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).
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97   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).
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106   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.
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110   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).
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115   3D raster statistics
116       3D raster statistics can be calculated with r3.stats and r3.univar.
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118   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.
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123   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.
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128       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.
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132   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.
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136       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.
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142       Alternatively,  GRASS  3D  raster  maps  can  be  imported and exported
143       from/to Vis5D (r3.in.v5d, r3.out.v5d).
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145   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".
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149   See also
150           ·   Introduction into raster data processing
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152           ·   Introduction into vector data processing
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154           ·   Introduction into image processing
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156           ·   Introduction into temporal data processing
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158           ·   Projections and spatial transformations
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160           ·   wxGUI 3D View Mode
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162           ·   m.nviz.image
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SOURCE CODE

165       Available at: 3D raster data in GRASS GIS source code (history)
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167       Main  index | 3D raster index | Topics index | Keywords index | Graphi‐
168       cal index | Full index
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170       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual
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174GRASS 7.6.0                                                   raster3dintro(1)
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