LIDAR Frequently Asked Questions Thursday, May 14, 2009
What is LIDAR?

LIDAR stands for LIght Detection and Ranging. It uses the same principle as RADAR except that it uses a laser instead of radio waves. One of the principle uses for LiDAR is for the measurement of elevation. For a more complete explanation of LiDAR, visit the NASA's LiDAR tutorial page at http://www.ghcc.msfc.nasa.gov/sparcle/sparcle_tutorial.html.

   

When will the entire state be covered?

-and-
What areas of the state are covered?
As of April 2009, the LIDAR data on Atlas now covers all land areas of the state of Louisiana!
   
In what (file) format is the LIDAR stored?

The file format of the LIDAR will depend on the form of representation of elevation data. In its raw form, LiDAR is a series of points stored as x, y, z where x and y can be longitude and latitude; z is the elevation in meters or feet. A simple ASCII file where each line has a coordinate (x,y,z) separated by commas (tabs, spaces, etc.) can be used to represent the data.

Another representation for LIiDAR data is as contours lines. The lines can be stored in a number of different CAD and GIS file formats.

A third representation for LIDAR data is as a digital elevation model (DEM). This is a raster format with a matrix (grid) with rows and columns. Each cell is of a fixed sized relative to the earth's surface; each cell holds the average elevation calculated from LIDAR points for that area of the earth's surface represented by the cell.

There are additional ways to represent LIDAR data such as triangular irregular networks (TIN) and profiles.

   
What data formats does Atlas use to represent LIDAR data?

Currently, Atlas has LIDAR data in four different forms: contours, digital elevation models, edited points, and raw points. The contour data is in shapefile format. The digital elevation models are in the USGS DEM format. The point data - both raw and edited - are in ASCII csv (comma separated value) files.

Also, Atlas has the breakline data that was used in the process to create the contour data. This breakline data is available as a shapefile coverage and is downloadable along with the other data formats.

   
What programs can I use to view the DEM files?

Any program that can read a USGS DEM file. Bentley Inroads, ERDAS Imagine, ESRI ArcGIS (with the Spatial Analyst extension), and Geomedia Grid are a few of the programs that can read USGS DEM files.

CAD programs such as AutoDesk AutoCAD and Bentley MicroStation can not read DEM files directly, but there are extensions (or companion products) that allow a CAD user to use DEM files with these CAD programs. Examples are Bentley's Inroads and AutoCAD Civil 3D. Most Civil Engineering applications read USGS DEMs.

   
I need a large number of DEMs, and downloading the files will take forever! How I can get a CD with the LIDAR data that I need? Arrangements are being made to supply the LIDAR data on CDs.
   
Can I get the LIDAR in other formats? Arrangements are being made to offer LIDAR in different formats. Keep watching Atlas for details.
   
What is the difference between "raw" LIDAR data and "modified" LIDAR data? The elevation points of the "raw" LIDAR data include elevations for buildings, highway overpasses, forest canopy, and anything else that prevented the laser beam from reaching "bare earth." Using post-processing methods, analysts can "remove" the obstructions and create a set of "modified" elevations points.
   
When was this LiDAR data made? The flights first took place in 1999. Check the metadata that is stored within each downloadable Winzip for further details.
   
Where can I find more information on LIDAR data for Louisiana? The Louisiana Oil Spill Coordinators Office (LOSCO) along with LSU and 3001, Inc., has created a document titled "The Louisiana Statewide LIDAR Project" to provide further information about the LIDAR available on Atlas. The document includes such information as pre-processing steps, acquistion, post-process steps, and future procurements. The document is available as a PDF file. Click here to view or download the PDF file. (This PDF was added Thursday, May 6, 2004.)

On Thursday, May 14, 2009, the QA/QC reports for the fifty-five (55) task areas are available for downloading on Atlas via the LIDAR downloader. Each LIDAR panel belongs to one of the 55 task areas. To download all fifty-five (55) reports in one zip file, click here.