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Using LIDAR Data

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ArcGIS | ArcView | ERDAS Imagine | Binary Raster File Format

ArcGIS^® 8.x

Load binary raster files:

1. Open ArcToolbox^®.
2. Expand Conversion Tools; then expand Import to Raster.
3. Double-click Floating Point Data to Grid.
4. Specify the input float file (*.flt) and create a name for the output file. Click OK and the file will be processed.

The LIDAR data is now ready for use in the ArcMap^® environment as an ESRI GRID file.

You may find it useful to download the LIDAR Data Handler. This ArcMap extension provides a set of tools that you may find useful for working with grids, including the capability to load the binary raster LIDAR data directly into ArcMap.

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ArcView^® 3.x

Load binary raster files:

1. Start ArcView.
2. Load Spatial Analyst. (This is necessary!)
3. Under the File menu, choose Import Data Source.
4. From the Import Data Source dialog that appears, select Binary Raster.
5. Choose your binary raster file from the Import Binary Raster Files dialog.
6. Create a name for the output grid.
7. You may be prompted to add the grid to the view — choose Yes.

You may find it useful to download the LIDAR Data Handler. This ArcView extension provides a set of tools that you may find useful for working with grids.

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ERDAS Imagine^® 8.x

Load binary raster files and georeference the data:

1. Start Imagine.

Import Data

2. Open Import/Export window by clicking on Import button.
3. Select Generic Binary as the type.
4. Select File as the media.
5. Select input binary raster file (.flt) downloaded from LDART.
6. Click OK, and the Generic Binary Data window appears.
   1. Select IEEE 32 Bit Float for the data type.
   2. Enter the nrows and ncols values from the header file (.hdr) that accompanies the binary raster file into the #Rows and #Cols fields. It should be in the same directory where the Zip file was extracted. Click OK.
7. Importing Generic Binary Data status window appears. Click OK when it is finished importing.
8. Click Close on Import/Export window.

Display and Georeference Data

9. Open a viewer by clicking on the Viewer button.
10. From the menu, select File=>Open=>Raster Layer and choose the Imagine (.img) file you just created.
11. Click the "i" tool on the Viewer. An ImageInfo window appears. From the menu, choose Edit=>Change Map Model.
    1. In the Pixel size X and Pixel size Y fields, enter the cell size value from the header file.
    2. In the Upper Left X field, enter the xllcorner value from the header file.
    3. In the Upper Left Y field, calculate the value: yllcorner + (nrows*cellsize) (values retrieved from the header file).
    4. In the Units field, enter the value from the Planar Distance Units in the metadata you received from LDART.
    5. Select the projection from the list provided. This information should be in the metadata you received from LDART. Click OK and choose Yes when the Attention dialog box appears.

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Binary Raster File Format

The binary raster file format is a simple format that can be used to transfer raster data between various applications. It consists of two files, the IEEE floating-point file and a supporting ASCII header file. The header file must have the same name as the data file, but with a .hdr file extension. The header data includes the following keywords and values:

ncols – number of columns in the data set.

nrows – number of rows in the data set.

xllcenter or xllcorner – x-coordinate of the center or lower-left corner of the lower-left cell.

yllcenter or yllcorner – y-coordinate of the center or lower-left corner of the lower-left cell.

cellsize – cell size for the data set.

nodata_value – value in the file assigned to cells whose value in unknown. This keyword and value is optional.

nodata_value – defaults to -999999.

byteorder – the byte order of the binary cell values.

You can choose between two keywords, msbfirst or lsbfirst.

Msbfirst is used for cell values written with the most significant bit first. Lsbfirst is used for cell values written with the least significant bit first.

For example,
ncols 480
nrows 450
xllcorner 378923
yllcorner 4072345
cellsize 30
nodata_value -999999
byteorder msbfirst

The nodata_value for the LIDAR ATM data set is -999999.

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