LAS Format LiDAR Files

ENVI allows you to read and convert LAS-format LiDAR data with the .las extension into ENVI raster or ENVI vector (.evf) files.

View the LAS LiDAR File Header

The header associated with the LAS LiDAR file is accessible as a text file. From the Toolbox, select LiDAR > View LAS Header.

The header file dialog is non-editable, but you save it as a text file which is printable. If the LAS LiDAR file has geospatial data associated with the file, the information appears below the Projection Information heading in the LAS header.

Convert LAS File to Raster/Vector

  1. From the Toolbox, select LiDAR > Convert LAS File to Raster/Vector. The Enter LAS Filenames dialog appears.
  2. Select the file with the .las extension and click Open. The Output Lidar Parameters dialog appears.
  3. Select an option for the data conversion from the Output Format drop-down list:
    • ENVI Raster File (default): Rasterizes the LAS data, creating output in a standard ENVI image file where the pixel values correspond to surface height or intensity. The converted data format results in an ENVI format file.
    • ENVI Vector File: Creates an ENVI vector file (.evf) in which each vector point record corresponds to an (x,y) pair of the LiDAR data with the elevation, intensity, and return number stored as corresponding attributes. Each point is converted to a vector item and the options for model type, output images, interpolation, pixel size, and output data type are desensitized.
  4. If you selected ENVI Raster File, select one of the following from the Model Type drop-down list:
    • Last Return (default): Also known as the bare Earth model, the last return corresponds to a pulse return from the last (lowest) surface to return a pulse. This can include solid materials, such as bare Earth, that are under semi-transparent vegetation. Solid objects such as buildings that do not have any transparency are also returned.
    • Full Feature: This model returns an average value of all the returns at a given (x,y) location.
    • First Return: Also known as the first pulse return, this model corresponds to a pulse return from the first (highest) surface. This model can include returns from the top of any semi-solid object, such as vegetation.
  5. Select the output image type from the Output Image(s) drop-down list. If your Output Format setting is ENVI Vector File, then both elevation and intensity are saved as attributes to the vector file. The following options are available:
    • Elevation and Intensity (default): The output file contains a digital elevation model (DEM) of the surface height, and an intensity image.
    • Elevation: The output file contains only the DEM of the return height.
    • Intensity: The output file contains only the intensity image.
  6. To determine the data projection saved in the DEM or vector file, click Select Output Image Projection. This option is available only if the LAS file has associated geospatial information. The default settings shown are the projection information of the input LAS data file.

    7. Select a projection type from the list, or click New to build a customized map projection.

  7. Enter the X Pixel Size and Y Pixel Size in the data in the specified projection units. This setting is required if you selected ENVI Raster File for the output format. The default values are set to 5.0.

    8. If projection information exists for the data file, then the units are the same as the units of the chosen projection. If no projection information exists, then the units are the same as the stored units of the data (unknown, meters, feet, and so forth).

    Be sure the values in the X Pixel Size and Y Pixel Size fields use the specified Units.

  8. If the output format is ENVI Raster File Interpolation, specify the interpolation to use to create a regular grid of interpolated Z values, using IDL’s TRIGRID function. The choices are:
    • Linear (default): Creates a regular grid of linear interpolated Z values.
    • Quintic: Creates a smooth interpolation performed using quintic polynomials. If the Extrapolate Edges parameter is set to Yes, the Interpolation parameter automatically defaults to Quintic and cannot be changed (linear interpolation does not extrapolate to the edges).
  9. If the output format is ENVI Raster File, click the Extrapolate Edges toggle button to Yes to extrapolate the boundary node indices within the geographic bounding box defining the dataset. The default is No.
  10. Use the Background Value field to assign the Z value to pixels outside of the calculated triangles. This setting is required if you selected ENVI Raster File for the output format. The default is 0.0000.
  11. Choose one of the following ENVI data types from the Output Data Type drop-down list: Byte, Integer (default), Unsigned Int, Long Integer, Unsigned Long, Floating Point, Double Precision, 64-bit Integer, Unsigned 64-bit. This setting is required if you selected ENVI Raster File for the output format. Select Floating Point, or Double Precision for highest data fidelity.
  12. Select output to File or Memory.
  13. Click OK. ENVI converts the data and adds it to the Layer Manager.