Kirk Waters

by Monday, January 28, 2013 @ .

I’m a physical scientist at the NOAA Coastal Services Center. In my spare time, when I’m not torturing co-workers, I try to fit in some technical work on lidar processing and distribution. I also try to figure out ways to improve the Digital Coast’s data offerings in general. Somewhere in the back of my head there are still a few brain cells that remember satellite ocean color, oceanographic field work, and something about the ozone hole.

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Digital Coast and its predecessor have been delivering custom lidar data for about 15 years now. One aspect that has always annoyed people is the limit on the amount of data you can get. In 1998, the system (then LDART) limited you to 5 million points at a time. The limit is now 500 million points, but that still won’t get some data sets in their entirety. We’ve changed the way we store our point data so it is compressed and that has allowed us to put the data where you can pick up big chunks at once. For those of you that just want to jump in and figure it out for yourselves, click here.

Use the map to find the data

Going to that link leaves a bit to be desired in terms of finding the data you want. If you’d rather use a map to narrow down the list of data, use the Digital Coast Data Access Viewer (DAV). When you do a search and get your results (see figure), any elevation data sets set up for direct download will have an ‘LAZ fmt’ link in them. Just hit that link and you’ll go straight to the directory with the data. One downside is that it builds an html index page listing all the files and that can take some time, so expect a little delay.

how to download data from digital coast data access viewer.png
Digital Coast results showing the LAZ fmt link with a big red arrow pointing to it. Also notice the 2007 data that would have been too big to add to the cart for the area selected, but has an LAZ fmt link.

Downloading lidar

One of the most important files in the list is the 0README.html file (the zero in the name is so it will sort to the top). It gives some information about how to download the files in bulk because you don’t really want to click on 1000 LAZ files individually. In addition to the LAZ files, you’ll also find an index shapefile with the file bounding boxes and the metadata file.

LAZ and compression

The LAZ files are the result of compressing the original LAS files with the free and lossless LASzip utility. The same utility will uncompress them. We’ve generally seen about a 7:1 compression ratio, making the lidar files small enough that we could even think about offering them this way (or you could think about downloading them). You can also find tools that will work directly with LAZ format at www.lastools.org, and I’m expecting we’ll see more and more GIS packages directly supporting LAZ in the future.

Custom lidar data

Of course, while downloading in this way gets you all the data in point cloud format, including all the returns and point classifications, it doesn’t give you the custom derived products, projections, or subsets that the DAV does. You can always get the data through DAV if you need custom output, including getting the data in LAZ format.

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