gis- raster data processing in grass

7/27/2019 GIS- Raster Data Processing in GRASS

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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.html


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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.html


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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.html


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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.html


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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.html


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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.html


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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

gis- raster data processing in grass

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