1r.fillnulls(1) Grass User's Manual r.fillnulls(1)
2
6 r.fillnulls - Fills no-data areas in raster maps using spline interpo‐
7 lation.
8
10 raster, surface, elevation, interpolation, splines, no-data filling
11
13 r.fillnulls
14 r.fillnulls --help
15 r.fillnulls input=name output=name method=string [tension=float]
16 [smooth=float] [edge=integer] [npmin=integer] [segmax=integer]
17 [lambda=float] [--overwrite] [--help] [--verbose] [--quiet]
18 [--ui]
19 Flags:
21 --overwrite
22 Allow output files to overwrite existing files
23 --help
25 Print usage summary
26 --verbose
28 Verbose module output
29 --quiet
31 Quiet module output
32 --ui
34 Force launching GUI dialog
35 Parameters:
37 input=name [required]
38 Name of input raster map
39 output=name [required]
41 Name for output raster map
42 method=string [required]
44 Interpolation method to use
45 Options: bilinear, bicubic, rst
46 Default: rst
47 tension=float
49 Spline tension parameter
50 Default: 40.
51 smooth=float
53 Spline smoothing parameter
54 Default: 0.1
55 edge=integer
57 Width of hole edge used for interpolation (in cells)
58 Options: 2-100
59 Default: 3
60 npmin=integer
62 Minimum number of points for approximation in a segment (>segmax)
63 Options: 2-10000
64 Default: 600
65 segmax=integer
67 Maximum number of points in a segment
68 Options: 2-10000
69 Default: 300
70 lambda=float
72 Tykhonov regularization parameter (affects smoothing)
73 Used in bilinear and bicubic spline interpolation
74 Default: 0.01
75
77 r.fillnulls fills NULL pixels (no data areas) in input raster map and
78 stores filled data to a new output raster map. The fill areas are
79 interpolated from the no data area boundaries buffer using v.surf.rst
80 regularized spline interpolation with tension (method=rst) or
81 r.resamp.bspline cubic or linear spline interpolation with Tykhonov
82 regularization.
83
85 Each area boundary buffer is set to three times the map resolution to
86 get nominally three points around the edge. This way the algorithm
87 interpolates into the hole with a trained slope and curvature at the
88 edges, in order to avoid that such a flat plane is generated in a hole.
89 The width of edge area can be adjusted by changing the edge parameter.
90 During the interpolation following warning may occur when using the RST
92 method:
93 Warning: strip exists with insufficient data
95 Warning: taking too long to find points for interpolation--please
96 change the region to area where your points are
97 This warning is generated if large data holes exist within the surface.
99 As the idea of r.fillnulls is to fill such holes, the user may ignore
100 the warning. The interpolation will be continued. However, the user may
101 pay attention to below notes.
102 If interpolation fails, temporary raster and vector maps are left in
104 place to allow unfilled map hole (NULL area) identification and manual
105 repair.
106 When using the default RST method, the algorithm is based on v.surf.rst
108 regularized splines with tension interpolation module which interpo‐
109 lates the raster cell values for NULL data areas from the boundary val‐
110 ues of the NULL data area. An eventual raster MASK is respected during
111 the NULL data area(s) filling. The interpolated values are patched into
112 the NULL data area(s) of the input map and saved into a new raster map.
113 Otherwise, either the linear or cubic spline interpolation with
114 Tykhonov regularization can be selected (based on r.resamp.bspline).
115
117 Depending on the shape of the NULL data area(s) problems may occur due
118 to an insufficient number of input cell values for the interpolation
119 process. Most problems will occur if a NULL data area reaches a large
120 amount of the map boundary. The user will have to carefully check the
121 result using r.mapcalc (generating a difference map to the input map
122 and applying the "differences" color table with r.colors) and/or to
123 query individual cell values.
124 RST method stores temporary maps on hard disk. It will require at least
126 as much free space as one extra input raster map takes.
127
129 In this example, the SRTM elevation map in the North Carolina sample
130 dataset location is filtered for outlier elevation values; missing pix‐
131 els are then re-interpolated to obtain a complete elevation map:
132 g.region raster=elev_srtm_30m -p
133 d.mon wx0
134 d.histogram elev_srtm_30m
135 # remove SRTM outliers, i.e. SRTM below 50m (esp. lakes), leading to no data areas
136 r.mapcalc "elev_srtm_30m_filt = if(elev_srtm_30m < 50.0, null(), elev_srtm_30m)"
137 d.histogram elev_srtm_30m_filt
138 d.rast elev_srtm_30m_filt
139 # using the default RST method to fill these holes in DEM
140 r.fillnulls input=elev_srtm_30m_filt output=elev_srtm_30m_rst tension=20
141 # using the bilinear method to fill these holes in DEM
142 r.fillnulls input=elev_srtm_30m_filt output=elev_srtm_30m_bilin method=bilinear
143 d.histogram elev_srtm_30m_rst
144 d.rast elev_srtm_30m_rst
145 d.erase
146 d.histogram elev_srtm_30m_bilin
147 d.rast elev_srtm_30m_bilin
148 r.mapcalc "diff_rst_bilin = elev_srtm_30m_rst - elev_srtm_30m_bilin"
149 r.colors diff_rst_bilin color=differences
150 r.univar -e diff_rst_bilin
151 d.erase
152 d.rast diff_rst_bilin
153 d.legend diff_rst_bilin
154
156 · Mitas, L., Mitasova, H., 1999, Spatial Interpolation. In:
157 P.Longley, M.F. Goodchild, D.J. Maguire, D.W.Rhind (Eds.), Geo‐
158 graphical Information Systems: Principles, Techniques, Manage‐
159 ment and Applications, Wiley, pp.481-492
160 · Mitasova H., Mitas L., Brown W.M., D.P. Gerdes, I. Kosi‐
162 novsky, Baker, T.1995, Modeling spatially and temporally dis‐
163 tributed phenomena: New methods and tools for GRASS GIS. Inter‐
164 national Journal of GIS, 9 (4), special issue on Integrating
165 GIS and Environmental modeling, 433-446.
166 · Mitasova H. and Mitas L. 1993: Interpolation by Regularized
168 Spline with Tension: I. Theory and Implementation, Mathemati‐
169 cal Geology 25, 641-655.
170 · Mitasova H. and Hofierka L. 1993: Interpolation by Regularized
172 Spline with Tension: II. Application to Terrain Modeling and
173 Surface Geometry Analysis, Mathematical Geology 25, 657-667.
174
176 r.fill.dir, r.mapcalc, r.resamp.bspline, v.surf.rst
177
179 Markus Neteler, University of Hannover and Fondazione Edmund Mach
180 Improvement by Hamish Bowman, NZ
181 Last changed: $Date: 2018-08-27 18:33:07 +0200 (Mon, 27 Aug 2018) $
183
185 Available at: r.fillnulls source code (history)
186 Main index | Raster index | Topics index | Keywords index | Graphical
188 index | Full index
189 © 2003-2019 GRASS Development Team, GRASS GIS 7.4.4 Reference Manual
191GRASS 7.4.4 r.fillnulls(1)