Compress and optimize your Lidar data in ArcGIS 10.2.1


The year 2014 has started with some seriously interesting news from Esri Inc. , and of special interest to ArcGIS Desktop users who use Lidar data in their day-to-day work.

On January 7, Esri released the new version of ArcGIS for Desktop – 10.2.1- and introduced a new image format call zLAS, which will be used to compress and optimize large collections of Lidar datasets, and which will be supported as a “direct-read” format in the new version of the software.

ArcGIS for Desktop v.10.2.1 is now available for the general public and you can login to the Customer Care Portal to download it. For those of you using ArcGIS 10.1 and 10.2 there is no need to uninstall your ArcGIS Desktop as v10.2.1 will be installed on top of your existing version.

In addition to the desktop release a new tool was released by the Imagery team which has been made available through the ArcGIS Resources website. This tool is called LAS optimizer and it can be downloaded for free here: http://www.arcgis.com/home/item.html?id=787794cdbd384261bc9bf99a860a374f

LAS Optimizer allows you to compress your LIDAR data (*.LAS), producing a set of *.zLAS files – an optimized version of the input Lidar datasets, which can be used for sharing, publishing and archiving.

The tool doesn’t require a license, and the output files it produces (*.zlas) can be used in ArcGIS 10.2.1.

Once you’ve downloaded the tool, extract it to a folder on your hard drive. If you have a 64-bit machine, run the ExLAS.exe. Otherwise use the ExLAS_32.exe.

Locate the folder with (the) LAS files and choose the operation: compress or decompress (if you’d already created any zLAS datasets).

Image

The tool only has a few parameters: you can choose whether to let it scan your LAS files or read the information about projection as well as statistics from the header.

We tested the tool with a relatively small collection of LAS files – just 82 with the total size of 5.45 Gb and it worked pretty well.  The tool produced 82 zLAS files with the total size of 591 Mb.

Have a look at how the data was compressed:

Before (RAW LAS files):

Image

After (compressed and optimized zLAS):

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The LAS Optimizer tool uses several optimization techniques:
- Lossless compression
- Spatial Indexing
- Generates statistics
- It is also a “direct-read” format in ArcGIS 10.2.1

Some technical details and specifications are listed in the Esri LAS OptimizerHelp.pdf which can be downloaded along with the tool.

There is only one known limitation so far: The compressed data is not editable in ArcGIS for Desktop. If you want to introduce any changes, let’s say change something in the classification codes in your data, you will have to decompress your zLAS files

Terms of use are found on the Esri Resource Center.

You can use the zLAS files in ArcGIS 10.2.1 similar to raw *.LAS files. For instance, zLAS can be used as input datasets for 3D Analyst tools or they can be added to a LAS Dataset, as below:

1. Use the Catalog Window in ArcMap to create a new LAS Dataset:

Image

2. Right-click the new LAS Dataset, choose Properties and navigate to the LAS Files tab. Click Add Files

3. Browse to your folder containing the zLAS compressed files and add them to the LAS Dataset.

Image

4. Add surface constraints (optional) and verify statistics. Note that statistics should have been calculated by the LAS Optimizer Tool:

Image

Sometimes the LAS files (raw lidar data) are being supplied without any information about the projection or coordinate system in the header. But this information is normally available in the metadata. You may need to use one of the free tools, such as Create PRJ for LAS (see the URL below) to assign a projection prior to using the LAS optimizer and adding LAS files to a LAS dataset.

Good luck with your Lidar processing in ArcGIS and don’t forget to check out other amazing free LIDAR processing tools available on the 3D GIS resource page: http://resources.arcgis.com/en/communities/3d/index.html

3 thoughts on “Compress and optimize your Lidar data in ArcGIS 10.2.1

  1. Jarlath O'Neil-Dunne

    Putting your data in zLAS makes it essentially worthless. Even Esri tools cannot do many basic tasks with it (e.g. creating an index). As daily a user of Esri products I am completely baffled why they went the zLAS route. Friends don’t let friends use zLAS. Here’s hoping that Esri eventually comes around to providing support for LAZ.

    Reply
    1. gsumerling

      Hello Jarlath,

      Esri will be applying full support for zLAS with the release of the 10.3 product suite in the coming months. In addition in 2015 Esri will be releasing an API for zlas which will allow other vendors to read and write to the zlas format.
      The original purpose of the zlas format was not only compression but also speed. zlas is also spatially indexed. The stats in the .lasx file include what class codes are in the files so when you add them to a dataset it knows about the classification and can set up the legend accordingly. In addition the performance of the server based analysis and distribution of the LiDAR data is improved by supply zlas data. There is a good discussion about the zlas format on the Esri blog http://bit.ly/10uD0NA

      hope this helps in some way

      Gordon S

      Reply

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