Rotating XYZ

[Ron Gilad]

Is there a way to rotate the point cloud using a rotation matrix?
Or to rotate it 3 times around each axis?

Regards,

 

Ron Gilad

GIS Engineer

M: +972-54-789-4543 

LinkedIn | Twitter | Website 

 

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[Martin Isenburg]

Hello Ron.

a call to las2las with the '-h' switch lists the currently supported coordinate transformations:

[...]

Transform coordinates.

  -translate_x -2.5

  -scale_z 0.3048

  -rotate_xy 15.0 620000 4100000 (angle + origin)

  -translate_xyz 0.5 0.5 0

  -translate_then_scale_y -0.5 1.001

  -transform_helmert -199.87,74.79,246.62

  -transform_helmert 598.1,73.7,418.2,0.202,0.045,-2.455,6.7

  -switch_x_y -switch_x_z -switch_y_z

  -clamp_z_below 70.5

  -clamp_z 70.5 72.5

  -copy_attribute_into_z 0

  -copy_intensity_into_z

[...] 

 

If you can express your transformation as a seven parameter "Helmert transformation" then you should be okay already. Otherwise your rotations are limited to be around an axis that is sticking out of the x/y plane with '-rotate_xy 15.0 620000 4100000'. However, the way las2las has evolved is through requests such as yours. Can you formulate exactly what kind of transformations you need to do and how you would like to see them formulated as a command line?

Regards.

Martin @rapidlasso

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[Ron Gilad]

The helmert transformation is perfect.

Angles are in rad or deg?

 

Ron Gilad

GIS Engineer

M: +972-54-789-4543 

LinkedIn | Twitter | Website 

 

[Michael Perdue]

Hi Martin,

Depending on the magnitude of Ron's rotation's, the helmert transformation will not work as it has been implemented in lastools. Consider the example below.

>echo "100 0 0" > foo.txt

>las2las -i foo.txt -iparse xyz -rotate_xy 10.0 0 0 -o bar.txt -oparse xyz

# Correct results

>cat bar.txt

98.4807753 17.3648178 0.00

#angles are in arc seconds. 36000s is 10deg

>las2las -i foo.txt -iparse xyz -transform_helmert 0,0,0,0,0,36000,0 -o bar.txt -oparse xyz

# incorrect results  

>cat bar.txt

100.0000000 17.4532925 0.00

The problem is that you are using small angle simplifications in your helmert transformation. For geodetic transformations, this is fine because the angles are generally very very small (usually measured in arc seconds or mas in modern transformations). But for larger rotation angles, the assumptions are no longer valid and the math applied in the rotation matrix breaks down.

Personally, I would like to see the helmert transformation in las2las support the full trigonometric solutions. These transformations are useful for applying arbitrary coordinate transformations and are commonly used to move back and forth between local grids and projected coordinates. But the rotations in these transformations are generally too big to use small angle simplifications.

Also note that your helmert transformation appears to be set up for the coordinate frame rotation convention commonly used in North America. Position vector rotations are the other convention and are more common in Europe. Does las2las have a switch allowing support of both?

Cheers,

Mike

[Martin Isenburg]

Hello,

the Helmert Transform in LAStools (see las2las -h) is set up to work with the TOWGS84 parameters provided for most EPSG codes.

Regards.

Martin

[xiaojun LIANG]

Hello,Martin

Do you mean clockwise or anticlockwise about the rotate angle?

 In addition, only one coordinate point is given, and the other point is 0,0?

Thanks.

Xiaojun.

在 2018年11月27日星期二 UTC+8下午1:23:16，Martin Isenburg写道：