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Raster Data
Processing inGRASS
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What is GRASS GIS?
-Geographic Resources Analysis Support System
-Open Source GIS, developed since 1984
-Portable code (multi-OS, 32/64bit)
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GNU/Linux MacOSX
MS-Windows
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What is a Raster Map?
-is a data layer consistingof a gridded array ofcells.
-has a certain number ofrows and columns,with a data point ineach cell.
- exist as a 2D grid or as a3D cube made up ofmany smaller cubes
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General rules in GRASS:
Raster output maps have their bounds
and resolution equal to those of the
current computational region.
Raster input maps are automatically
cropped/padded and rescaled (using
nearest-neighbour resampling) to
match the current region.
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Raster input maps are automatically masked
if a raster map named MASK exists. The
MASK is only applied when reading maps
from the disk.
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Raster map import/export
Since GRASS handles data in its own format, GIS files
need to be imported (r.in.gdal) or just registered
(r.external)
Raster maps are exported with r.out.gdal into common
formats. Also r.out.bin, r.out.vtk, r.out.ascii and
other export modules are available. They export the
data according to the current region settings.
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Metadata
r.info
-region extent
-data range-data type
-creation history, and other metadata.
r.support-updates metadata (map title, units, vertical
datum etc.)
http://grass.osgeo.org/grass64/manuals/html64_user/r.info.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.support.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.support.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.support.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.support.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.info.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.info.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.info.html7/27/2019 GIS- Raster Data Processing in GRASS
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Metadata
-Timestamps are managed with r.timestamp.
- Region extent and resolution are mangagedwith r.region.
http://grass.osgeo.org/grass64/manuals/html64_user/r.timestamp.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.region.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.region.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.timestamp.html7/27/2019 GIS- Raster Data Processing in GRASS
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Raster map operations
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Resampling Methods and Interpolation
Methods
GRASS raster map processing is always
performed in he current region settings. If the
resolution differs from that of the input raster
map(s), on-the-fly resampling is performed
(nearest neighbor resampling). If this is not
desired, the input map(s) has/have to be
resampled beforehand with one of thededicated modules.
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r.resample uses the built-in resampling, so it should
produce identical results as the on-the-fly
resampling done via the raster import modules
r.resamp.interp
Resampling with nearest neighbor, bilinear, and
bicubic method: method=nearest uses the
same algorithm asr.resample.
r.resamp.rst- Reinterpolates and computes topographic
analysis from input raster file to a new raster
file (possibly with different resolution) using
regularized spline with tension and smoothing
Modules are available for Reinterpolation
of "filled" raster maps
http://grass.osgeo.org/grass64/manuals/html64_user/r.resample.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.resamp.interp.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.resample.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.resamp.rst.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.resamp.rst.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.resample.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.resamp.interp.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.resample.html7/27/2019 GIS- Raster Data Processing in GRASS
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Modules are available for Reinterpolation
of "filled" raster maps
r.resamp.stats- Resamples raster map layers
using aggregation
r.fillnulls- Fills no-data areas in raster maps
using v.surf.rst splines interpolation)
http://grass.osgeo.org/grass64/manuals/html64_user/r.resamp.stats.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.fillnulls.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.fillnulls.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.resamp.stats.html7/27/2019 GIS- Raster Data Processing in GRASS
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Furthermore, there are modules available for
reinterpolation of "sparse" (scattered points
or lines) maps:
--Inverse distance weighted average (IDW)
interpolation (r.surf.idw and r.surf.idw2)
--Interpolating from contour lines
(r.contour)
http://grass.osgeo.org/grass64/manuals/html64_user/r.surf.idw.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.surf.idw2.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.contour.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.contour.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.surf.idw2.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.surf.idw.html7/27/2019 GIS- Raster Data Processing in GRASS
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NULL values: no value e.g. gaps in DEM
MASK:--MASK'ed cells are read as NULL cells ->
usually skipped also all areas outside the
computation region)
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NULL(perhaps due
to a MASK)
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Hydrologic modeling toolbox
Watershed modeling related modulesare r.basins.fill, r.water.outlet, r.watershed,and r.terraflow.
Water flow related modulesare r.carve, r.drain,r.fill.dir, r.fillnulls, r.flow,and r.topidx.
Flooding can be simulated with r.lake. Hydrologic simulation model are available
as r.sim.sediment,r.sim.water, and r.topmodel.
http://grass.osgeo.org/grass64/manuals/html64_user/r.basins.fill.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.water.outlet.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.watershed.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.terraflow.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.carve.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.drain.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.fill.dir.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.fillnulls.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.flow.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.topidx.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.lake.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.sim.sediment.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.sim.water.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.topmodel.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.topmodel.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.sim.water.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.sim.sediment.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.lake.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.topidx.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.flow.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.fillnulls.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.fill.dir.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.drain.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.carve.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.terraflow.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.watershed.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.water.outlet.htmlhttp://grass.osgeo.org/grass64/manuals/html64_user/r.basins.fill.html7/27/2019 GIS- Raster Data Processing in GRASS
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Hydrological model
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Raster capabilities
Example raster module groups
-resampling
-Reprojection/georectification
-map calculator-Terrain analysis
-Hydrologic modeling
-Reports and statistics
Raster maps: DEMs, land cover, climatic maps
Imagery maps: Landsat, MODIS, SPOT, QuickBird
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Raster data analysis: further methods
Additional DEM analysis modules:
r.fill.dir depression areas can be
filled with
r.flow flowlines can be calculated
with
r.drain trace a flow through a DEM
r.watershed and r.terraflow watershed analysis can be
done with
r.cost cost surfaces
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Raster data analysis: Further methods Interpolation methods
v.surf.idw 2D inverse distance
weighted
r.surf.contour 2D from contour linesr.bilinear 2D bilinear
v.surf.rst 2D regularized splines with
tension (with cross
validation):v.vol.rst 3D regularized splines with
tension (with cross
validation):
v.kernel 2D/3D kernel densities
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Raster data analysis: Further methods
Energy:
Line of sight:
r.sunmask cast shadows, astronomical
calculations of sun position
r.sun energy budget
r.los viewsheds can be generatedwith