Good ol’ GIS.stackexchange … I finally ended up posting a bounty of 50 reputation points for my rotation problem, and got an answer within a couple of hours!

If you want to rotate a grid of points around (originX, originY) and degrees θ, enter the following values into the dialog (see image to the right):

Scale X |
cos(θ) |

Rotation Y |
-sin(θ) |

Translation X |
originX – cos(θ) * originX + sin(θ) * originY |

Rotation X |
sin(θ) |

Scale Y |
cos(θ) |

Translation Y |
originY – sin(θ) * originX – cos(θ) * originY |

Here’s an R function to give you the numbers directly:

## Compute correct affine numbers for qgsAffine plugin
affine

<- function(originX, originY, rotAngle

) {
A

<- rotAngle

* pi / 180
scaleX

<- scaleY

<- cos(A

)
rotX

<- sin(A

)
rotY

<- -sin(A

)
transX

<- originX

- cos(A

) * originX

+ sin(A

) * originY

transY

<- originY

- sin(A

) * originX

- cos(A

) * originY

aff

<- data.frame(scaleX, scaleY, rotX, rotY, transX, transY

)
return(aff

)
}
The respondent on GIS.SE initially gave a PostGIS (>v.1.5) function which would do the job – ST_Rotate:

SELECT ST_Rotate

(geom

, θ

*pi()/180, originX

, originY

)
I really want a solution which works just in QGIS, so for the moment am going to use the qgsAffine plugin, even though it’s a bit clunky to have to do the calcs, and the plugin itself seems buggy.

However, it should be possible to build a rotation function in spatialite, which comes installed with QGIS.

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Good ol’ GIS.stackexchange … I finally ended up posting a bounty of 50 reputation points for my rotation problem, and got an answer within a couple of hours! If you...

Hi, i’m trying to work with this tool to rotate a vector point grid, I calculate with a spreedsheet de values of rotation, scale and translation but when I run the vector affine transformation, the geometry of vector point grid do the rotation but change the location of the grid.

My coordinate System is: ESPG:2743 – Datum 73 /Modified Portuguese Grid.

This are the characteristics of the grid:

+proj=tmerc +lat_0=39.66666666666666 +lon_0=-8.131906111111112 +k=1 +x_0=180.598 +y_0=-86.98999999999999 +ellps=intl +towgs84=-223.237,110.193,36.649,0,0,0,0 +units=m +no_defs