[Qgis-user] How to calculate the transformation parameters for the QGIS Affine Plugin

[Germán Carrillo]

Just in case you  have R within reach, have a look at the post "Similarity
and affine transformations in R" [1], which explains how to use my R plugin
"vec2dtransf" to perform affine transformations.


Regards,

Germán
----
[1]
http://geotux.tuxfamily.org/index.php/en/geo-blogs/item/302-affine-and-similarity-transformations-in-r
[2] http://cran.r-project.org/web/packages/vec2dtransf/index.html





2014-10-07 13:59 GMT-05:00 Siki Zoltan <siki at agt.bme.hu>:

> Hello Marcel,
>
> to calculate affine transformation parameters you must have at least 3
> points in both coordinate systems.
> LV95_y = Y0 + a * local_y + b * local_x
>
> LV95_x = X0 + c * local_x + d * local_y
>
> If you set up the equations for the three points, you get to linear
> equation systems, one for Y0, a, b unknowns, and another fo X0, c, d
> unknowns.
>
> It is highly recommended to use more points and least squares estimation
> for the parameters.
>
> Best regards,
> Zoltan
>
>
>
> On Tue, 7 Oct 2014, Marcel Stadelmann wrote:
>
>  Hi,
>>
>> I would like to make an affine transformation with a vector layer shape
>> file, using the Affine Plugin. I know from two points the correct
>> coordinates:
>> local_y local_x LV95_y  LV95_x
>> 9.065056        7.70714 2753308.44      1166381.26
>> 9.065056        -5.085236       2753295.68      1166391.31
>>
>> How can I calculate the transformation parameters?
>>
>> Marcel
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>>
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