Add blank reserved space to the end of the header

[hobu]

1.5 is currently proposing to add three entries to the header – gpstime_offset, gpstime_max, and gpstime_min. We should add reserved space past this so no more future LAS versions change the header size. Additionally:

• all of the empty space should have 0's written in it
• the amount of space should bring us to some naturally aligned size

[esilvia]

Can you elaborate on the benefit of padding an arbitrary amount of space to the end of the header? Any reader can read the Header Size field and respond appropriately, and the existence of VLRs means that the full header will always be variable, by definition.

[hobu]

Can you elaborate on the benefit of padding an arbitrary amount of space to the end of the header?

We should add specification-reserved space to the end of the header. Each version we have increased the size of the header. Reserving space would (hopefully) stop us from bumping the size going forward. (I hope there is never a LAS 1.6, but 🤷)

[esilvia]

I see what you're saying, but why is changing the header size with minor version changes a problem that needs to be solved?

[abellgithub]

It may allow for fewer changes to readers and writers of the files with little/no downside.

[esilvia]

The recommended approach is to read the header size (2 bytes) from the LAS header at byte offset 94. I think at this point we'll leave it the way it is for LAS 1.x and continue with the current approach. If your reader would like to read a full 1000 or 65535 bytes when parsing the header, there is nothing to stop you.