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Using LAS Datasets to Create Functional Outputs

Using LAS Datasets to Create Functional Outputs

Now that we know where to download elevation data (see blog post titled “Obtaining Elevation Data from NOAA Digital Coast”), we can use these data for creating useful outputs and beautiful visual aids.

This blog post will discuss how to easily create a LAS dataset, and then how to produce both digital elevation models (DEMs) and hillshades from this LAS dataset. A LAS Dataset is a storage method for LAS files. LAS files are the industry standard file format in which airborne LiDAR data is stored. Within a LAS Dataset, all information is stored within a Point Cloud. This Point Cloud refers to the individual elevation points measured by the laser used in airborne LiDAR collection. Working within a LAS dataset is advantageous because it allows the user access to these individual points, and provides additional LAS dataset functionality that will not be discussed in this blog post.

For this tutorial, follow along using elevation data that you may have already downloaded for your area of interest. The sample data used within this tutorial focuses on the area of Block Island, Rhode Island. This small island off Rhode Island’s southern coast provides an iconic and distinctive shape to work with. If this is your first time visiting Block Island, this URL will help you orient yourself.

This post was written with Esri ArcGIS for Desktop 10.2.2 in mind, and assumes that you have at least a basic knowledge of working with this software, as well as elevation data terms such as "digital elevation model" and "hillshade."

First, let's create a new LAS dataset. Within the ArcCatalog window, right click on the folder in which you want to create a LAS dataset and select New > LAS Dataset.

  1. Double click on the newly created LAS Dataset in the Catalog window to open the LAS Dataset Properties box. Select the “LAS Files” tab.
    1. In the “Show” dropdown menu, select Folder (see green circle below).
    2. Click on Add Folders (see red circle below) and navigate to the folder containing the LAS files and select the folder.
    3. Click Apply and OK to exit the dialog.
      • In some cases it is not necessary to select an XY or Z coordinate system; this will automatically be determined from your data.
      • In other cases, the source LAS files will not come with a spatial reference. Before being input into a LAS dataset, it will be necessary to define the projections of each LAS file. To do this, follow these steps:
        • Visit this link and download the toolbox.
        • Open the README.pdf and follow instructions to install the toolbox. In ArcMap open your toolbox. Right click on the heading and select Add Toolbox.
        • Navigate to the folder indicated in the README.pdf file and click OK.
        • Next, open the Lidar Tools toolbox, and expand the Manage toolset. Open the Create PRJ for LAS and fill in the tool dialog. Once this is complete, please proceed with this workflow.

Next, drag the LAS Dataset into ArcMap's Table of Contents.

At first, only a red outline of the individual LAS files will show up. These are the footprints (or outlines) of each input LAS file. To see the individual points, zoom in.

Now, search for the Make LAS Dataset Layer tool using the search menu. Alternatively, this tool can be found within the Data Management Tools > Layers and Table Views > Make LAS Dataset Layer. Fill in the tool using the following inputs:

Note: It will be necessary to run this tool twice. Once to create the ground returns layer and one to create the all returns layer. See the two tool dialogs following the instructions below to verify parameters for each layer.

  1. Input = LAS dataset
  2. Output Layer  = name of output layer
  3. Class Codes =
    1. * To create Ground Return Layer select 2 (this is based on the ASPRS standard LiDAR classifications, seen below).

When creating an All Returns Layer, do not select any class codes.

  1. Return Values =
    1. * To create a Ground Returns Layer, do not select any return values.
    2. When creating All Returns Layer select all boxes in the Return Values Area.
  2. Leave the remaining fields as the defaults.
  3. Click OK to run tool.

Next, search for the LAS Dataset to Raster tool using ArcMap's search menu. This tool can also be found within the Conversion Tools > To Raster > LAS Dataset to Raster. Using the following inputs for to run the tool:

Note: It will necessary to run this tool twice; once for ground returns and once for all returns.

  1. Input = Select one of the temporary layers.
  2. Output = Output location and file name with file extension specified.
    1. We recommend .img as a good file extension. Please note that if no file extension is specified, or if a different file extension is specified, the user may experience an ArcGIS error.
  3. Sampling Value = desired cell size, the default is 10 (this will be 10 meters, or feet depending on the coordinate system of your data).
  4. Leave the remainder of the tool as default values.
  5. Click OK to run tool.

Congratulations! You have just created your first two digital elevation models! Next, we will create hillshades for your area of interest.

Start by searching for the Hillshade tool using the search menu. Alternatively, this tool can be found within the 3D Analyst Tools > Raster Surface > Hillshade. Using the following inputs, fill out the tool's dialog.

Note: It will necessary to run this tool twice; once for ground returns and once for all returns.

  • Input = All Returns Raster with .img file ending.
  • Output = filename with extension (recommend .img).
  • Leave the rest default.
  • RERUN FOR GROUND RETURNS.
  • Click OK to run tool.

Here is an example of the Digital Elevation Model (DEM) that was created for All Returns.

Here is an example of the Hillshade that was created for All Returns. In areas of more dramatic elevation, this hillshade would be much more pronounced.

 

This blog posting was developed with the support of a competitive grant (cooperative agreement number P09AC00212; task agreement number P13AC00875) from the National Park Service in partnership with the North Atlantic Coast Cooperative Ecosystems Studies Unit.  It is part of a larger document available for download on the IRMA Portal.

 

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Authored by

erica
 

Last updated

09/10/2015 - 08:38