.TH v.transform 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBv.transform\fR\fR  \- Performs an affine transformation (shift, scale and rotate) on vector map.
.SH KEYWORDS
vector, transformation, geometry, GCP
.SH SYNOPSIS
\fBv.transform\fR
.br
\fBv.transform \-\-help\fR
.br
\fBv.transform\fR [\-\fBtwxyab\fR] \fBinput\fR=\fIname\fR  [\fBlayer\fR=\fIstring\fR]  \fBoutput\fR=\fIname\fR  [\fBxshift\fR=\fIfloat\fR]   [\fByshift\fR=\fIfloat\fR]   [\fBzshift\fR=\fIfloat\fR]   [\fBxscale\fR=\fIfloat\fR]   [\fByscale\fR=\fIfloat\fR]   [\fBzscale\fR=\fIfloat\fR]   [\fBzrotation\fR=\fIfloat\fR]   [\fBcolumns\fR=\fIname\fR[,\fIname\fR,...]]   [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-t\fR" 4m
.br
Shift all z values to bottom=0
.IP "\fB\-w\fR" 4m
.br
Swap coordinates x, y and then apply other parameters
.IP "\fB\-x\fR" 4m
.br
Swap coordinates x, z and then apply other parameters
.IP "\fB\-y\fR" 4m
.br
Swap coordinates y, z and then apply other parameters
.IP "\fB\-a\fR" 4m
.br
Swap coordinates after the other transformations
.IP "\fB\-b\fR" 4m
.br
Do not build topology
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input vector map
.br
Or data source for direct OGR access
.IP "\fBlayer\fR=\fIstring\fR" 4m
.br
Layer number or name (\(cq\-1\(cq for all layers)
.br
A single vector map can be connected to multiple database tables. This number determines which table to use. When used with direct OGR access this is the layer name.
.br
Default: \fI\-1\fR
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output vector map
.IP "\fBxshift\fR=\fIfloat\fR" 4m
.br
Shifting value for x coordinates
.br
Default: \fI0.0\fR
.IP "\fByshift\fR=\fIfloat\fR" 4m
.br
Shifting value for y coordinates
.br
Default: \fI0.0\fR
.IP "\fBzshift\fR=\fIfloat\fR" 4m
.br
Shifting value for z coordinates
.br
Default: \fI0.0\fR
.IP "\fBxscale\fR=\fIfloat\fR" 4m
.br
Scaling factor for x coordinates
.br
Default: \fI1.0\fR
.IP "\fByscale\fR=\fIfloat\fR" 4m
.br
Scaling factor for y coordinates
.br
Default: \fI1.0\fR
.IP "\fBzscale\fR=\fIfloat\fR" 4m
.br
Scaling factor for z coordinates
.br
Default: \fI1.0\fR
.IP "\fBzrotation\fR=\fIfloat\fR" 4m
.br
Rotation around z axis in degrees (counter\-clockwise)
.br
Default: \fI0.0\fR
.IP "\fBcolumns\fR=\fIname[,\fIname\fR,...]\fR" 4m
.br
Name of attribute column(s) used as transformation parameters
.br
Format: parameter:column, e.g. xshift:xs,yshift:ys,zrot:zr
.SH DESCRIPTION
\fIv.transform\fR performs an affine transformation (translate and rotate) of a
vector map. An affine transform includes one or several linear transformations
(scaling, rotation) and translation (shifting). Several linear transformations
can be combined in a single operation. The command can be used to georeference
unreferenced vector maps or to modify existing geocoded maps.
.SH NOTES
Coordinate transformation based on Ground Control Points (GCPs) is done
by \fIv.rectify\fR and not supported by
\fIv.transform\fR.
.PP
Transformation parameters (i.e. \fIxshift\fR, \fIyshift\fR,
etc.) can be fetched from attribute table connected to the vector
map. In this case vector objects can be transformed with different
parameters based on their category number. If the parameter cannot be
fetched from the table, default value is used instead.
.PP
Note that the transformation matrix can be printed by
\fIm.transform\fR.
.SH EXAMPLE
.SS DXF/DWG drawings
.PP
Most DXF/DWG drawings are done within XY coordinate space. To transform
them to a national grid, we can use \fIv.transform\fR together with
\fIv.rectify\fR and a first\-order transformation.
.br
.nf
\fC
v.transform \-t in=watertowerXY out=watertower_z zscale=0.04 zshift=1320
v.rectify in=watertower_z out=watertowerUTM points=wt.points order=1
\fR
.fi
.SS Extrude 2D vector points to 3D based on attribute column values
Spearfish example with manual table editing for vertical shift:
.br
.nf
\fC
# work on own map copy:
g.copy vect=archsites@PERMANENT,myarchsites
# add new \(cqzs\(cq column to later store height of each site:
v.db.addcolumn myarchsites col=\(dqzs double precision\(dq
v.db.update myarchsites layer=1 column=zs value=\(dqcat * 1000\(dq
# perform z transformation:
v.transform \-t input=archsites output=myarchsites3d column=\(dqzshift:zs\(dq table=\(dqarchsites_t\(dq
# drop table containing transformation parameters:
echo \(dqdrop table archsites_t\(dq | db.execute
\fR
.fi
The resulting map is a 3D vector map.
.SS Extrude 2D vector points to 3D based on attribute column values
Spearfish example with automated elevation extraction for vertical shift:
.br
.nf
\fC
# work on own map copy:
g.copy vect=archsites@PERMANENT,myarchsites
# add new \(cqzs\(cq column to later store height of each site:
v.db.addcolumn myarchsites col=\(dqzs double precision\(dq
# set region to elevation map and fetch individual heights:
g.region raster=elevation.10m \-p
v.what.rast myarchsites rast=elevation.10m col=zs
# verify:
v.db.select myarchsites
# perform transformation to 3D
v.transform \-t myarchsites output=myarchsites3d column=\(dqzshift:zs\(dq layer=1
# drop table containing transformation parameters
v.db.dropcolumn myarchsites3d col=zs
\fR
.fi
The resulting map is a 3D vector map.
.SH SEE ALSO
\fI
m.transform,
i.rectify,
v.rectify,
r.region
\fR
.SH AUTHOR
Radim Blazek, ITC\-irst, Trento, Italy,
.br
Column support added by Martin Landa, FBK\-irst (formerly ITC\-irst), Trento, Italy (2007/09)
.SH SOURCE CODE
.PP
Available at: v.transform source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual