Note: This addon document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade your GRASS GIS installation, and read the current addon manual page.
Four parameters are required in input:
The following maps can be generated in output:
The change detection map is created using the classified angle map and applying
a threshold to the magnitude: the change is given by the pixels that have
values higher than the threshold, divided in four categories depending on
the quadrant they belong to.
The threshold can be chosen manually (custom value, given by personal
criteria) or using statistical criteria. In this case the mean of the magnitude
values is used and the user can choose the multiples of N standard
deviation to sum to the mean (threshold = mean + N * standard deviation).
One could consider of running the module at first without assigning a
threshold, in order to have an idea of the range of the magnitude and to
choose an appropriate custom threshold (for univariate statistical parameters
run r.univar). In this case i.cva gives
in output only three maps: the angle, angle classified and magnitude maps.
# compute tasscap of 1987 scene g.region raster=lsat5_1987_10 -p i.tasscap sensor=landsat5_tm \ input=lsat5_1987_10,lsat5_1987_20,lsat5_1987_30,lsat5_1987_40,lsat5_1987_50,lsat5_1987_70 \ output=lsat5_1987_tasscap # compute tasscap of 2002 scene g.region raster=lsat7_2002_10 -p i.tasscap sensor=landsat7_etm \ input=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40,lsat7_2002_50,lsat7_2002_70 \ output=lsat7_2002_tasscap # compute CVA i.cva xaraster=lsat5_1987_tasscap.1 xbraster=lsat7_2002_tasscap.1 \ yaraster=lsat5_1987_tasscap.2 ybraster=lsat7_2002_tasscap.2 \ output=CVA_87_02 stat_threshold=1 Calculating DeltaX and DeltaY Writing angle map CVA_87_02_angle Writing magnitude map CVA_87_02_magnitude Mean of magnitude values is: 0.091335330260002 Standard deviation of magnitude values is: 0.0671211630131731 Writing change detection map CVA_87_02_change Threshold is 0.158456493273
CVA angle map 1 |
CVA classified angle map |
CVA magnitude map |
CVA change map |
Optionally, labels can be added to the four quadrants of the change map (after Zanchetta et al., 2016):
# assign legend cat i_cva_legend_rules.csv 1:moisture reduction 2:chlorophyll increase 3:moisture increase 4:bare soil increase r.category map=CVA_87_02_change separator=":" rules=i_cva_legend_rules.csv # assign colors cat i_cva_color_rules.csv 1 217:255:0 2 10:214:10 3 75:173:255 4 139:105:20 r.colors map=CVA_87_02_change rules=i_cva_color_rules.csv
Available at: i.cva source code (history)
Latest change: Mon Jun 28 07:54:09 2021 in commit: 1cfc0af029a35a5d6c7dae5ca7204d0eb85dbc55
Note: This addon document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade your GRASS GIS installation, and read the current addon manual page.
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© 2003-2023 GRASS Development Team, GRASS GIS 7.8.8dev Reference Manual