Geoscience Reference
In-Depth Information
lastindex
Produces a tile index from a number of LAS files in a vector format that is
supported by OGR
As a first example, we will convert a LAS file into a compressed LAZ file. We use
the LiDAR dataset
st-helens.las
(see Appendix A.1.3), acquired over Mount
Saint Helens (Skamania County in Washington state, USA).
With the option
--a_srs
we can assign the coordinate reference system. For the
st-helens dataset, the projection information is already set within the LAS file, but
this is not always the case. Moreover, not all LAS formats store the the projection
information in a similar way. From LAS 1.4 onward, the projection information
should be put in a variable length record (VLR), formatted in the open geospatial
consortium (OGC) well known text (WKT).
las2las --compressed --a_srs EPSG:26919 st-helens.las
→
st-helens.laz
The resulting LAZ file has a compression factor of 9.8, which is higher than aver-
age. We can inspect the file with the utility
lasinfo
. The first part of the reported
information summarizes the header and contains information on the compression, the
total number of point records (per return), the projection information, the minimum
and maximum values of X, Y and Z, etc.
lasinfo st-helens.laz
-----------------------------------------------------
Header Summary
-----------------------------------------------------
Version:
1.2
Source ID:
0
Reserved:
0
Project ID/GUID:
→
'00000000-0000-0000-0000-000000000000'
System ID: 'PDAL'
Generating Software: 'PDAL 9c974e46af'
File Creation Day/Year: 333/2012
Header Byte Size 227
Data Offset: 1312
Header Padding: 0
Number Var. Length Records: 5
Point Data Format: 3
Number of Point Records: 12388139
Compressed: True
Compression Info: LASzip Version 2.2r0 c2 50000:
→
POINT10 2 GPSTIME11 2 RGB12 2
Number of Points by Return:
12388139 0 0 0 0
Scale Factor X Y Z:
0.01 0.01 0.01
Offset X Y Z:
-0.00 -0.00 -0.00
Min X Y Z:
560022.41 5114840.63 1116.21
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