[LASlib] Change coordinate and the offset

[Jérôme Chatillon]

Hi everyone,

I'm unsing the LASlib to read and write las files.

I would like to apply a coordinate transformation and also use a different xyz offset for the output las file. how to properly do it ?

The following code work as long as the offset is not changed:
LASreadOpener lasreadopener;
lasreadopener.set_file_name( "input.las" );
LASreader* lasreader = lasreadopener.open();
LASwriteOpener laswriteopener;
laswriteopener.set_file_name( "output.las" );
LASwriter* laswriter = laswriteopener.open(&lasreader->header);

unsigned int count = 0;
double oY,iZ,oZ;
while (lasreader->read_point())
{
    transform(lasreader->point.get_x(), lasreader->point.get_y(), lasreader->point.get_z(), &oX, &oY, &oZ);
    lasreader->point.set_x(oX);
    lasreader->point.set_y(oY);
    lasreader->point.set_z(oZ);
    laswriter->write_point(&lasreader->point);
    laswriter->update_inventory(&lasreader->point);
    count++;
}

laswriter->update_header(&lasreader->header, TRUE);
laswriter->close(true);
delete laswriter;
lasreader->close(true);
delete lasreader;

Thanks
How can I change the output file offset at the same time ?

[Martin Isenburg]

Hello,

you can find an example in the open source code of las2las.cpp as this becomes necessary whenever reprojecting from one CRS to another. Below the distilled rundown that should work (minus whatever bugs this untested pseudo code has).

Regards,

Martin @rapidlasso

============

// open lasreader

LASreader* lasreader = lasreadopener.open();

// create new header for output

LASheader header = lasreader->header;

// zero the pointers of the old header so they don't get deallocated twice

lasreader->header.unlink();

// transform the center of bounding box to new position

F64 point[3];

point[0] = (header.min_x +  header.max_x)/2;

point[1] = (header.min_y +  header.max_y)/2;

point[2] = (header.min_z +  header.max_z)/2;;

transform(point, point);

// use position to create better suited offsets

header.x_offset = ((I64)((point[0]/header.x_scale_factor)/10000000))*10000000*header.x_scale_factor;

header.y_offset = ((I64)((point[1]/header.y_scale_factor)/10000000))*10000000*header.y_scale_factor;

header.z_offset = ((I64)((point[2]/header.z_scale_factor)/10000000))*10000000*header.z_scale_factor;

// open laswriter

LASwriter* laswriter = laswriteopener.open(&header);

// read and write points

while (lasreader->read_point())

{

   lasreader->point.compute_coordinates();

   transform(lasreader->point.coordinates, lasreader->point.coordinates);

   // create XYZ quantized with new quantizer

   lasreader->point.compute_XYZ(&header);

   laswriter->write_point(&lasreader->point);

   laswriter->update_inventory(&lasreader->point);

}

// update header and destroy writer

laswriter->update_header(&lasreader->header, TRUE);

laswriter->close();

delete laswriter;

// destroy reader

lasreader->close();

delete lasreader;

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[Jérôme Chatillon]

Hi Martin,

I did try to copy the header and modify it, but i didn't know about the unlink() function: brilliant :)
It's all working as I expected.

Merci :)

Jérôme Chatillon

[Martin Isenburg]

I guess you saw the bug:

[...]

// update header and destroy writer

laswriter->update_header(&lasreader->header, TRUE);

[...]

should be

[...]

// update header and destroy writer

laswriter->update_header(&header, TRUE);

[...]

Martin

--

http://rapidlasso.com - fast code to transform your LiDARs

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