[Liblas-devel] Re: LASzip versus LT compressor

[Martin Isenburg]

good point, michael.

i should have made more clear what question i was trying to answer:

when i talk to folks who consider using LASzip to compress their large LIDAR
archives for faster download and cheaper archival (e.g. CLICK,
OpenTopography, NCALM, NOAA, various state and county agencies, ...) the
very same question eventually arises: "how LASzip compares to the LIDAR
compressor from Lizard Tech in terms of compression ratio and speeds". it
was in that context that i was doing these side-by-side experiments and
reporting the results.

and yes. it is true that LASzip does not support selective decompression ...
yet. (-;

cheers,

martin @lastools

On Wed, Apr 27, 2011 at 3:17 PM, Michael Rosen <mrosen at lizardtech.com>wrote:

> One thing that needs to be made clear is what we mean when we say "decode
> time."  Specifically, are we decoding the whole thing, or small piece of the
> whole thing?  Those are both important questions but they occur in different
> workflows.  When you extract from a static archive, you care about how long
> it takes to recover your original file.  When you render a scene from a
> working format, you care about how long it takes extract that scene.  MrSID
> compression was designed to be a working format, allowing reasonable
> performance without decoding the entire dataset.  If I understand Martin's
> note, the decode timing being compared is exactly the full dataset.  Those
> are two separate workflows.
>
> Here are my original remarks on this:
>
> >  WRT extraction time, for smaller files, the MG4?s computational overhead
> (*) favors LAZ for all but the smallest extractions
> >  For larger files, the "break even" point is much further to the right.
> >  For larger files, with very small extractions, the built-in  index of
> MG4 allows faster extractions than raw (unindexed) LAS.
>
> Here's a link to a presentation I gave on this last February:
> http://prezi.com/y90nhhyucxra/lidar-distribution-challenges-and-solutions/
>
> If you zoom into the "Compression" part you can see the graphs on this.
>
> msr
>
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