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v.transform(1) Grass User's Manual v.transform(1)

v.transform - Performs an affine transformation (shift, scale and rotate) on vector map.

vector, transformation, geometry, GCP

v.transform
 
v.transform --help
 
v.transform [-twxyab] input=name [layer=string] output=name [xshift=float] [ yshift=float] [zshift=float] [ xscale=float] [yscale=float] [ zscale=float] [zrotation=float] [columns=name[,name,...]] [-- overwrite] [--help] [--verbose] [--quiet] [--ui]

-t
 
Shift all z values to bottom=0
-w
 
Swap coordinates x, y and then apply other parameters
-x
 
Swap coordinates x, z and then apply other parameters
-y
 
Swap coordinates y, z and then apply other parameters
-a
 
Swap coordinates after the other transformations
-b
 
Do not build topology
--overwrite
 
Allow output files to overwrite existing files
--help
 
Print usage summary
--verbose
 
Verbose module output
--quiet
 
Quiet module output
--ui
 
Force launching GUI dialog

input=name [required]
 
Name of input vector map
 
Or data source for direct OGR access
layer=string
 
Layer number or name (’-1’ for all layers)
 
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.
 
Default: -1
output=name [required]
 
Name for output vector map
xshift=float
 
Shifting value for x coordinates
 
Default: 0.0
yshift=float
 
Shifting value for y coordinates
 
Default: 0.0
zshift=float
 
Shifting value for z coordinates
 
Default: 0.0
xscale=float
 
Scaling factor for x coordinates
 
Default: 1.0
yscale=float
 
Scaling factor for y coordinates
 
Default: 1.0
zscale=float
 
Scaling factor for z coordinates
 
Default: 1.0
zrotation=float
 
Rotation around z axis in degrees (counter-clockwise)
 
Default: 0.0
columns=name[,name,...]
 
Name of attribute column(s) used as transformation parameters
 
Format: parameter:column, e.g. xshift:xs,yshift:ys,zrot:zr

v.transform 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.

Coordinate transformation based on Ground Control Points (GCPs) is done by v.rectify and not supported by v.transform.
Transformation parameters (i.e. xshift, yshift, 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.
Note that the transformation matrix can be printed by m.transform.

Most DXF/DWG drawings are done within XY coordinate space. To transform them to a national grid, we can use v.transform together with v.rectify and a first-order transformation.
 
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

Spearfish example with manual table editing for vertical shift:
 
# work on own map copy:
g.copy vect=archsites@PERMANENT,myarchsites
# add new ’zs’ column to later store height of each site:
v.db.addcolumn myarchsites col="zs double precision"
v.db.update myarchsites layer=1 column=zs value="cat * 1000"
# perform z transformation:
v.transform -t input=archsites output=myarchsites3d column="zshift:zs" table="archsites_t"
# drop table containing transformation parameters:
echo "drop table archsites_t" | db.execute
The resulting map is a 3D vector map.

Spearfish example with automated elevation extraction for vertical shift:
 
# work on own map copy:
g.copy vect=archsites@PERMANENT,myarchsites
# add new ’zs’ column to later store height of each site:
v.db.addcolumn myarchsites col="zs double precision"
# 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="zshift:zs" layer=1
# drop table containing transformation parameters
v.db.dropcolumn myarchsites3d col=zs
The resulting map is a 3D vector map.

m.transform, i.rectify, v.rectify, r.region

Radim Blazek, ITC-irst, Trento, Italy,
 
Column support added by Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy (2007/09)
Last changed: $Date: 2015-08-07 05:24:55 +0200 (Fri, 07 Aug 2015) $

Available at: v.transform source code (history)
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© 2003-2018 GRASS Development Team, GRASS GIS 7.4.3 Reference Manual
GRASS 7.4.3

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