[GIS] Laz LiDAR files displaying extremely long thin line of points

laslazlidarvisualisation

I am having difficulty properly visualizing aerial LIDAR data from the csc.noaa.gov source.

Taking any of the .laz files, the point cloud displays as an extremely long thin line of points. Zoomed in, there are cyclic perturbations in the points along that line, which leads me to believe that some sort of transform is necessary to properly visualize the data. For comparison sake, the aerial LIDAR data set found in opentopo.sdsc.edu visualizes as one would expect.

Both claim to use NAD83 as the horizontal coordinate system. From what I can tell, the only major difference is one is las 1.0 and one is las 1.2. That being said, I don't really know what I'm doing.

A little bit of background to help guide an answer. I do not come from a GIS background, but rather am interested in comparing my LIDAR point clouds against a geographically accurate model, say a quality aerial LIDAR collect. For now, while learning, I have been using the free applications LAStools and CloudCompare.

Best Answer

This is because csc.noaa.gov lidar files are stored with the .laz file format extension. It is a compressed version for .las extension.

Read this* article to know more about compressed las files (.laz).

In order to correctly visualize these types of files, you need to retransform them from .laz to .las. Use the open-source LiDAR compressor LASzip to accomplish this task.

Here is one example:

Suppose that LASZip is installed under the drive C:, and the .laz file is stored under a fold named project (C:\project). Do the following:

c:\LASZip\laszip -i c:\project\aaa.laz -o c:\project\aaa.las

aaa is just a name for the file which I have made up. Here is more some tips from Bruce Simonson about potentializing the use of LasZip .

*Reference

ISENBURG, M. LASzip: lossless compression of LiDAR data, 2012.

Examples

See below some examples about how .laz files become disfigured in comparison with its uncompressed version .las.:

This is the Fugro Viewer. While the dots in the .las file are concentrated in the upper and lower layers in the z direction (left panel), the dots in the .laz version are more homogeneously spread (right panel).

enter image description here

This is the Quick Terrain Reader. The dots in the .laz file are flattened in the z direction (right panel).

enter image description here

Related Solutions

[GIS] Converting LiDAR files from LAZ to LAS format

For running LASzip from the command prompt window it is also necessary to specify the path of the input file.

For example, suppose the laszip.exe file is installed under the drive D: (D:\LASzip\laszip.exe) and that the .laz files are stored in D:\lidar.

Then, type:

D:\LASzip\laszip D:\lidar\*.laz

It will decompress all LAZ files in the current folder overwriting any existing file. The output files will have same name as the input files (but with extension .las).

Some remarks:

it is not necessary to type the file extension '.exe' in the command-line.
one can also use the identifier -i for input parameter, but it is optional: D:\LASzip\laszip -i D:\lidar\*.laz.
the identifier -odir can be used to specify a different output folder: D:\LASzip\laszip -i D:\lidar\*.laz -odir D:\lidar\output. It will save all .laz files with the same file names (except for .las extension) in the specified output folder. See Saving LAZ files to different location from input (LAS) files?.
use the identifier -odix to append to output file names: D:\LASzip\laszip -i D:\lidar\*.laz -odir D:\lidar\output -odix _decompressed. It means if the input file name is point_cloud_27.laz, the output file name will be point_cloud_27_decompressed.las.

See more examples here.

Another option (in relation to first example) is to proceed as suggested by Barbarossa, i.e., open the cmd from the input file folder and write the command as in your first attempt.

REM move to folder where the input file is, then run laszip.
cd  D:\lidar
D:\LASzip\laszip *.laz

If you want to call laszip directly from any folder without specifying the program path, then, berniejconnors's answer gives a good hint to add it in the environment variables (see here).

laszip D:\lidar\*.laz

All examples here work the other way around, i.e., converting from .las files to .laz.

[GIS] Why did Esri create .zlas compressed LiDAR files instead of adopting .laz

I can see no technical reason for ESRI's creation of zLAS. A decision was made that - as far as I understand - was quite heavily contested even within the ESRI management to create a format under their control. There was a big outcry by the Open Source Geospatial Consortium (OSGeo).

At the time a number of misleading statements were circulated that are disputed here. The "LAZ clone" (how I always called it) neither (de-)compresses faster nor is more compact than LAZ. It adds intensity histograms (that should really have been proposed as an addition to LAS to the ASRPS LAS Working Group that ESRI is a member of). It adds an optional point reordering step and integrates a spatial index. All this already existed/exists for the open source LAZ compressor.

I repeatedly tried to get ESRI to the table and work with the community on the open source solution. It happened at the time the LAZ compressor needed an upgrade for the new LAS 1.4 point types anyways. I again and again asked ESRI to tell us what technical features they needed so badly for LiDAR compression, so we could design a joint solution. The frustration of ESRI not even bothering to respond ultimately led to this very successful April Fools Day joke.

LAZ has not really changed in response to zLAS. Esri never communicated which ingenious technical detail had made their "LAZ clone" necessary:

The intensity histograms were not added to LAZ. This should happen at the LAS specification level to be useful for all. Instead of proposing an amendment to the specification, Esri cooked their own soup. I chose not to repeat this way of acting for LAZ, but continue to encourage Esri to propose this.
LASzip is order preserving which allows streaming. The compressor does not attempt to rearrange points for better compression. How to best reorder points is described here and a freeware tool called 'lasoptimize' exists.
One thing that "kind of" happened was better API support for spatial indexing with LAX files in the open source LASzip dynamic linked library interface. But this would have happened eventually anyways.
What happened as a direct response was a slowdown to the LAS 1.4 design process as I was waiting for Esri to maybe change their mind and cooperate. In the meantime the "LAS 1.4 compatibility" mechanism was added to LASzip to hold folks over.
When with 2 years delay due to my pointless waiting for Esri the native LAS 1.4 extension for LAZ was released, it contained zero contributions from Esri. The new "selective decompression" and "variable chunking" features had been been planned before.

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Related Solutions

[GIS] Converting LiDAR files from LAZ to LAS format

[GIS] Why did Esri create .zlas compressed LiDAR files instead of adopting .laz

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