The American Surveyor

LIDAR Data Retrieval Tool (LDART) – Data for Mapping Coastal Topography in the U.S

LTD-Admin

(January, 2004) LIDAR Data Retrieval Tool (LDART) is a Web-based application that the NOAA Coastal Services Center developed to allow its customers, partners, and employees to select topographic LIDAR data from its collection.

The tool enables users to customize their output data set. Users may interactively select geographic boundaries, projections, horizontal and vertical datums, and output file formats. It is hoped that LDART can be used by coastal managers, coastal geologists, and the general public to generate custom beach-elevation data sets for use in decision making, research, and for general information.

Using LDART

Using the LDART data retrival system users are first promted to supply brief contact information. NExt, list of available flight missions is presented. Upon selecting a data set, the user is presented with a graphic view of the data and can then navigate the scene in order to select the required data eextents to be extracted – note: a maximum file size is in effect.

Users can Access LDART Data by visiting http://www.csc.noaa.gov/cgi-bin/crs/tcm/ldart_start.pl


Data Retrival Tool Map display

Notable Features

  • A visible image product may be generated along with the topographic data set.
  • Elevation contours may be generated and output as an ArcView® shapefile.
  • Additional data layers are available to assist in defining spatial bounds.
  • Zoom in map control allows "rubber-band" zooming.
  • Refine extent map control allows precise control over selection of spatial bounds.
  • A link is provided for help on selecting spatial bounds.
  • The polygons defining the survey coverage more accurately represent actual coverage.
  • New projection options are available for special state projections (Oregon, California, & Michigan).
  • Mission selection is now on the first page. The mission list is now sorted by state and year of survey.
  • All ATM elevation data within LDART are now QA/QC level 3
  • All ATM elevation data within LDART have now been spatially filtered to remove noise. The filtering method is documented in the metadata

Tip: Loading binary raster files in ArcView GIS

  • Load Spatial Analyst (required)
  • Under the File menu, choose Import Data Source.
  • From the Import Data Source dialog that appears, select Binary Raster.
  • Choose your binary raster file from the Import Binary Raster Files dialog.
  • Create a name for the Output Grid.
  • 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.

 This extension requires the user to have Spatial Analyst, because the tools in the handler were developed to work with the Arc/Info Grid format. You can use data that you downloaded from LDART and interpolated to a surface, or you can download some sample data files below that have been interpolated already. These files are in the binary raster file format, which is described in the metadata for each file

Download the Data Handler extension here

Data Loader allows you to rename and load data files downloaded using the LIDAR Data Retrieval Tool (LDART) into a view within ArcView.

  • There are five options for working with the Legend:
  • Legend Scaler allows you to interactively scale a legend (AVL file) to your range of data or any range that you want.
  • Legend Scaler Plus allows you to interactively manipulate the scaling of an active legend based on a selected color ramp and specified scaling options.
  • Add Color Ramp allows you to add the color ramp associated with an active legend to an existing or new color ramp file.
  • Legend Loader allows you to apply a legend (AVL file) to any number of selected grids at once.
  • ColorMap Editor allows you to edit the red, green and blue (RGB) values of any of the classes in the grid legend.
  • Grid Profiler allows you to create profiles or transects across selected grid themes. There are three options that allow you to manipulate and extract grid data:
  • Grid Subtractor allows you to subtract one grid from another.
  • Cut/Fill Calculator allows you to calculate volume and area gained and lost from a difference grid (such as one calculated by Grid Subtractor).
  • Grid Clipper clips a grid by a selected polygon theme or graphic. This can be useful if you want to calculate differences for a small section of your grid. Graphic To Shape allows you convert a selected graphic (perhaps one that you have used to clip a grid) to a polyline or polygon theme.

    LDART data projection information

    LDART uses the National Geodetic Survey model, GEOID99, for conversions between NAD83 ellipsoid heights and NAVD88 orthometric heights. The GEIOD99 model is less accurate near the coast. It may be necessary to apply a local orthometric height datum correction to the LIDAR elevation values to compensate for limitations within the model. This will ensure the most accurate comparisons between elevations derived in reference to orthometric heights.

    Useful Weblinks:

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