How to convert USGS airborne lidar .las files (from USGS' CLICK) to DEMs and TINs in ArcMap 10

1st return DEM made from 0.7m ground sample distance airborne lidar of a section of the Denver Metro Area. Natural Neighbor was used to interpolate the point data to a raster format. Image was generated in ArcScene by draping the DEM over itself.

Goal:

• To convert (free) USGS airborne lidar .las files to DEM or TIN formats in ArcMap 10

Software:

• ESRI ArcMap with 3D Analyst Extension and Spatial Analyst Extension

Steps:

1. Download and extract/unzip an airborne lidar .las file from the USGS Center for Lidar Information Coordination and Knowledge (CLICK) site. Read through the metadata .xml file. For this tutorial, 2008 Denver Metropolitan Area and 2010 Grand County, Colorado airborne lidar were used. Beware that with a high resolution nominal pulse spacing down to 0.7 meters, a rather small coverage .las file (e.g., 110 MB) easily contains about 7 million points.
2. In ArcMap 10 ArcToolbox: LAS to Multipoint (3D analyst > Conversion > From file > LAS to Multipoint). Use the extracted .las file as input file.
   • point spacing - set this to match the point spacing found in the .las metadata .xml file (I used 0.7 for the Denver Metro Area .las)
   • For 1st return (buildings and vegetation included), Input Class Code - leave this blank; Input Return Values as 'LAST_RETURNS' only
   • For bare earth (buildings and vegetation removed; ground surface only), Input Class Code - specify as 2, Input Return Values 'ANY_RETURNS' (more about codes, etc., here, and with a focus on forestry applications here).
   • In 'Environments' enable Z and disable M.
3. From the Multipoint file, generate a preliminary view of

   'Point to raster' DEM of an area just north of Grand Lake, CO as viewed in ArcScene. Format is .tif, cell assignment type is MEAN, cell size is 6, and value field is Shape.Z.

   your data in a raster format: Use 'Point to Raster' (ArcToolbox > Conversion Tools > To Raster > Point To Raster). 'Point to Raster' does not interpolate the point data -- so depending on the cell size used, there will be holes in the output DEM. Below are 'Point to Raster' steps extracted from this Jan. 2011 ESRI White Paper.
   • A DEM or DSM can be built directly from the multipoint feature class using the Point to Raster tool. The tool takes a single feature class as input, is fast, and gives results suitable for most forestry applications. The disadvantage with this tool is that NULL value cells will appear in the raster where no returns are encountered.
   • The export formats supported by the Point to Raster tool include, but are not limited to, .tif, .img, and Esri GRID.
   • The Point to Raster tool is initialized from the Conversion Tools toolbox (ArcToolbox\Conversion Tools\To Raster\Point To Raster). On the form, select:
     • The input multipoint feature class
     • The value field, which is the shape field from the multipoint feature class (This contains the z-heights for the feature)
     • The output raster (If the intended raster is an Esri GRID file, do not place an extension on the file name. If the output is TIFF, terminate the file name with .tif.)
     • A cell assignment of MEAN or MAX (Set the MEAN values for an average surface height. Setting the value to MAX is useful when producing a first return, canopy surface.)
     • A cell size (This is important. Too fine, and the surface will have many NoData cells; too coarse, and the surface will lose detail. A good rule here is four times the average point spacing. In this example, the average point spacing is 0.6, so a cell size of 3 meters is optimal [2.4 rounded up to the highest whole meter].)
4. ONLY COMPLETE THIS STEP (STEP #4) IF YOU WANT TO POPULATE YOUR LIDAR FILE WITH XYZ VALUES (IMPORTANT: Step #4 is not necessary in order to generate DEMs and TINs: Both formats can be generated directly from the Multipoint file created in step #2 above). If a cursory look at the data is not helpful, skip to step #5 (for DEM) or step #6 (for TIN).
   • In ArcMap 10 ArcToolbox: Multipart To Singlepart (data management tools> features > Multipart to Singlepart). Use the new multipoint file (created in step #2) as input features. In 'Environments' enable Z and disable M (note: Multipart to Singlepart can take a LONG TIME to process)
   • In ArcMap 10 ArcToolbos: Ad XY coordinates (Data Management Tools > Features > Add XY Coordinates). This will add x, y, and z fields. Use the multipoint file (created in step #2) as input. In 'Environments' enable Z and disable M (note: Add XY Coordinates can take a LONG TIME to process)
5. For a DEM: Interpolate using Natural Neighbor. In ArcMap 10 ArcToolbox: (Spatial Analyst Tools > Interpolation > Natural Neighbor). DEMs can be generated directly from the Multipoint file or from the file into which the XYZ coordinates were created (results are same). If using the Multipoint file, make sure 'Z value field' is set to 'Shape.Z'. If using the file into which the XY coordinates were generated, make sure the 'Z value field' is set to 'POINT_Z' ). Either way, use the pull down menu in the Natural Neighbor window to set this.
   • Note: Spline also works well with lidar data: Like Natural Neighbor, the new surface will pass directly through the known points
   • Note: Interpolating the Z value using the default cell size (around 6 m for this example) will produce very similar results as the 'Point to Raster' DEM generated above in step #3. Differences are that 1) there are no holes (NoData) in the DEM and 2) when the cell size is reduced to values closer to the average point spacing of the lidar data (like 3 m), more detail can be extracted from the dense point cloud.
   • Note: The USGS offers some 1/9 arc-second (3 m) raster DEMs that were generated from lidar and other sources here.
6. For a TIN: A TIN can be created directly from a Multipoint file (see step #2) or from the file into which the XY coordinates were generated (see step #5). In ArcMap 10 ArcToolbox: (3D Analyst Tools > TIN Management > Create TIN). Set the 'Imput Feature Class' to the Multipoint file OR to the file with the XY Coordinates. For the former, make sure the 'height_field' is set to Shape.Z (use the pull-down list to find Shape.Z); for the latter, again using the pull-down list, make sure the 'height_field' is set to POINT_Z.
   • Here is the result in ArcScene (and with contours) and here is the result in ArcMap.