value of "reserved" field in VLR / EVLR

[Martin Isenburg]

Hello,

digging through some LAS history I found that in the first 1.0 specification of the LAS format there was a requirement for the VLR header to start with a "Record Signature" that was specified as "Record Signature: The record signature is a two byte data field that must contain 0xAABB.". I guess I used this specification to implement the first version of LASlib:

top of page 5: 

http://www.asprs.org/wp-content/uploads/2010/12/asprs_las_format_v10.pdf

In later specifications this field of the VLR header is renamed to "reserved" and its value is left unspecified:

bottom of page 5: 

http://www.asprs.org/wp-content/uploads/2010/12/asprs_las_format_v11.pdf

middle of page 6:

http://www.asprs.org/wp-content/uploads/2010/12/asprs_las_format_v12.pdf

middle of page 7:

http://www.asprs.org/a/society/committees/standards/asprs_las_spec_v13.pdf

and only in the very latest version it is now mandated to be zero:

top of page 9:

http://www.asprs.org/wp-content/uploads/2010/12/LAS_1_4_r13.pdf

The current version of LASlib still sets this "reserved" field to 0xAABB whenever a new VLR is created. This is a heads up that the next release of LASlib will set this value to zero as dictated by the latest spec: "Reserved: This value must be set to zero".

Also for the Extended Variable Length Record (EVLR) header the "reserved" field must be set to zero

This observation grew out of a discussion in the LAStools user forum on how to correctly convert LAS 1.2 files with point types 1 to LAS 1.4 files with point types 6 including a proper OGC WKT string.

http://groups.google.com/d/topic/lastools/2mIhkedcp9I/discussion

Regards,

Martin @rapidlasso