Lidar and ArcGIS


Sometimes we get questions about using lidar data from Digital Coast in ArcGIS. We don’t always get any details about what data they’re having trouble with or which format it’s in, so today I’d like to make a quick pass over the various options we have for lidar data and derived products with a discussion of how they work in ArcGIS.

Data Access

Let’s start off with our two main mechanisms for getting data. First is our custom download application, the Data Access Viewer (DAV), that lets you subset the data, convert projections and datums, derive some product types, and choose an output format. The drawback is that there are size limits to what you can get and we’ll have to process it (no charge though). The second is the bulk download. Pretty much a web area with the files you can download for entire data sets. Not much in the way of choices, but you can grab it all. dav_phaseii_esri

If you get data from the DAV, it could be a point cloud, a DEM, or con
tours. If the data set name doesn’t have DEM in it, we’re starting from a point cloud and the DEM or contours will be derived from the point cloud upon request. It will be an automated process without breaklines. If the name does have DEM in it, we’re starting with a DEM someone made from the point cloud and likely applied breaklines and some manual labor to clean up artifacts. Here’s the output options and how they relate to ArcGIS:

Lidar Point Clouds

The DAV gives you the option of the formats for point clouds. The bulk download will all be in LAZ. Make sure you see the note at the end of this post if you’re planning to derive surfaces from the point clouds.

LAS

LAS format is a standard from ASPRS and is a very common format for airborne lidar. ArcGIS should have no problem reading this, including LAS version 1.4 (the newest). You just have to make a new LASD and add the LAS files to it. ESRI has a tutorial for that.

LAZ

This is an open source format for a compressed LAS file. The compressor/decompressor is laszip (free). ArcGIS does not like this format. They use a different compression called zLAS, however, that format is proprietary. To use LAZ with ArcGIS, you simply use the laszip tool above to convert to LAS and then proceed as normal. Note that all of the bulk download point clouds are in LAZ format, geographic coordinates, and NAVD88 vertical meters (except a few rare cases where that isn’t possible).

ASCII

The ASCII format option is a bit restricted. It is only going to give you the x,y,z values. If you want to do any filtering (e.g. only ground points), make sure you do it in the DAV because there won’t be any info later. This can be imported into ArcGIS the same way you’d import any other ASCII table of data.

Digital Elevation Models (DEM)

Digital Elevation Models are a raster format representing a surface interpolated from the point cloud data. Usually it’s only the ground points, though it doesn’t have to be. The DAV will give you a choice of output formats while the bulk download will typically have whatever was the original format for the data. The bulk download DEMs will be the solid earth points while you can make some choices, maybe too many, about what points to use.

GeoTIFF (*.tif)

Often just called TIFF files, these should work just fine in ArcGIS. The possible problem you might have is related to the no-data value. The base specification for TIFF does not have a tag for no-data, but you’ll often have DEMs that have void areas. Particularly in coastal areas. TIFF files will either use an IEEE not a number (NaN) value or will use an additional tag proposed by GDAL. Newer versions of ArcGIS should handle both of those. It’s possible you may need to force generation of statistics for it to recognize the NaNs.

Imagine (*.img)

This should also load into ArcGIS without any issues.

Arc Grid

While this will have no problem being read by ArcGIS, it isn’t an option for DAV and there shouldn’t be any in the bulk download. There might be some that we missed though. It’s a proprietary format, so we usually transform to TIFF or IMG  if we receive them.

Contours

Contours are currently only available by generating them in the DAV from point cloud data sets. There are two formats available, though I hope to add LandXML as a better solution for CAD users.

Shapefile (*.shp)

Shapefiles are an open format from ESRI and should have no problem importing into ArcGIS.

DXF (*.dxf)

The AutoCAD DXF format can be read into ArcGIS, but you’ll be happier with the shapefiles. We actually make a shapefile first and then convert to DXF, so there is nothing gained for an ArcGIS user to pick DXF.

 Deriving Products From Point Clouds

One final note to be aware of, particularly if you grabbed LAZ files from the bulk download site. When you create derived products from the point cloud, make sure to put your point data into the right projection first. For most people, this is a UTM or State Plane projection. The LAZ files on bulk download are in geographic coordinates, so the horizontal units do not match the vertical. This can confuse some software, especially if you specify the output grid units in feet or meters. The DAV will let you specify the projection you want.

Kirk Waters

I’m a physical scientist at the NOAA Office for Coastal Management. 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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