Coastal Services Center

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Frequently Asked Questions (FAQs)

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Many of the questions we receive about our Topographic Change Mapping project are similar in nature. Recognizing this, we have compiled this list of Frequently Asked Questions (FAQ). Some of the responses will direct you to contact the NOAA Coastal Services Center directly for more detailed answers.

• If I never received the e-mail from LDART, my data file had nothing in it, or LDART didn't work, what can I do?
• What do I do if I created a data file with LDART, but it is too large for me to download or work with?
• Why are the elevation values I downloaded much less than zero (-20 to -40 meters)?
• What is the binary raster format?
• How do I convert the binary raster files to ESRI grids in ArcView 3.x?
• How do I convert the binary raster files to ESRI grids in ArcGIS?

If I never received the e-mail from LDART, my data file had nothing in it, or LDART didn't work, what can I do?

You may have typed your e-mail address incorrectly, or LDART may have a bug. Try your request again, and if you still do not receive any messages, send an e-mail detailing your problem to csc@csc.noaa.gov and type "Attention: TCM Project Scientist" in the subject heading.

What do I do if I created a data file with LDART, but it is too large for me to download or work with?

Go back to LDART and choose a smaller area, or subsample your data using the "binning" option.

Why are the elevation values I downloaded much less than zero (-20 to -40 meters)?

The data you downloaded are most likely referenced to an ellipsoid surface. The values you are seeing are about the expected range for that vertical reference frame. To get values that are closer to "0=mean sea level" try either the NAVD88 or NGVD29 datum in the Vertical Datum selection box in the LDART applet. For help with the concept of a vertical datum see the NGS FAQ.

What is the binary raster 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.
• The 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.

How do I convert binary raster files to ESRI grids in ArcView 3.x?

1. Load the Spatial Analyst extension. (This is necessary!)
2. Under the File menu, choose Import Data Source.
3. From the Import Data Source dialog that appears, select Binary Raster.
4. Choose your binary raster file from the Import Binary Raster Files dialog.
5. Enter a name for the Output Grid.
6. 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.

How do I convert binary raster files to ESRI grids in ArcGIS?

1. Start ArcToolbox.
2. Under the Conversion Tools->Import to Raster option, click the Floating Point Data to Grid option.
3. Enter a Input float file or use the browse button to locate the binary raster file.
4. Enter a name for the Output grid.
5. Click the OK button.

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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