v.transform(1grass)

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

KEYWORDS
vector, transformation, geometry, GCP

SYNOPSIS
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]

  Flags:

-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

  Parameters:

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

DESCRIPTION
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.

NOTES
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.

EXAMPLE

  DXF/DWG drawings

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

  Extrude 2D vector points to 3D based on attribute column values
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.

  Extrude 2D vector points to 3D based on attribute column values
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.

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

AUTHORS
Radim Blazek, ITC-irst, Trento, Italy,
Column support added by Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy (2007/09)

SOURCE CODE

Available at: v.transform source code (history)

Accessed: Friday Apr 04 01:20:35 2025

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