Extended Public Header Block Records + Point Data Records in LAS 1.4 PDF # 6-10

[Rose Phillips]

Hello everyone,

I've received a couple of LAS 1.4 PDF# 6 files with extended Public Header Block Records + Point Data Records.

I noticed in the example “upgraded” LAS 1.4 file in the URL below, there were extended public header block + point data records. 

https://rapidlasso.com/2016/01/10/create-proper-las-1-4-files-with-lastools-for-free/

The extended scan angle in my example file are significantly different than the min/max values in the standard header (assuming the extended_scan_angle is in 32bit int format)

e.g.

  scan_angle_rank   -30         29

..

  extended_scan_angle         -4999   4833

This was the same for the “upgraded” LAS 1.4 file in the URL above 

e.g. 

scan_angle_rank -24 24

..

extended_scan_angle -4000 4000

However I can't see these bigger scan angle values in lasinfo, Global Mapper Statistics, ArcGIS Las Dataset Statistics or pdal info. 

I was wondering if anyone knew the implications of having these extended records?

Do I ignore these extended records as artefacts of file processing/conversion?

Many thanks and kind regards,

Rose Phillips

[Jordan Gunn]

Hi Rose,

I believe the answer you are looking for is on page 99 (actually page 7 in the pdf) and page 101 (page 9 in the pdf) of this document. With that being said, I may be misunderstanding your question, if so I advise you to give this article a read, as your asswer will likely be in it. Regardless, this document was among the most useful I have ever read for understanding the LAS format (particularly LAS 1.4) in a practical sense. 

https://www.asprs.org/wp-content/uploads/2010/12/LAS_Specification.pdf  

Cheers,

Jordan

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[Vishnu Aarthi S]

Hello Team,

Hope you all are doing good. I have a point cloud dataset with RGB encoding. I need to convert it to FBX format. Is there any way to convert it? Is there any option available? Looking forward to hearing from you people.

Many thanks in advance.

Regards,

Vishnuaarthi S

Process Management  | www.dsmsoft.com

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[Martin Isenburg]

Hello,

https://rapidlasso.com/2016/01/10/create-proper-las-1-4-files-with-lastools-for-free/

The extended scan angle in my example file are significantly different than the min/max values in the standard header (assuming the extended_scan_angle is in 32bit int format)

e.g.

  scan_angle_rank   -30         29

..

  extended_scan_angle         -4999   4833

lasinfo records the raw integer values that are being stored.  For the "extended_scan_angle" of point types 6 to 10 the 16 bit signed integer numbers need to be multiplied with 0.006 in order to get the actual degrees. The older signed 8 bit "scan_angle_rank" of point types 0 to 5 stores the scan angle information with less resolution, only the nearest full degree is stored so no multiplication with a scale factor is necessary [note also that they do not cover the full 360 degree range].

-4999*0.006 = -29.994

4833*0.006 = 28.998

 

However I can't see these bigger scan angle values in lasinfo, Global Mapper Statistics, ArcGIS Las Dataset Statistics or pdal info. 

I was wondering if anyone knew the implications of having these extended records?

Do I ignore these extended records as artefacts of file processing/conversion?

Many people do not need the additional precision extended scan angle and continue to make decisions in terms of full integer degrees using the scan angle rank, for example, using the good old filters from las2las or many other LAStools. So far I have not had anyone requesting to filter angles at precisions higher than the full integers.

Filter points based on their scan angle.
  -keep_scan_angle -15 15
  -drop_abs_scan_angle_above 15
  -drop_abs_scan_angle_below 1
  -drop_scan_angle_below -15
  -drop_scan_angle_above 15
  -drop_scan_angle_between -25 -23