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LIDAR

What is LIDAR?

LIDAR is an acronym for LIght Detection And Ranging.  It is a measuring system that detects and locates objects on the same principle as radar but uses light from a laser.  In Johnson County's case this was airborne LIDAR that was flown similar to an aerial photography flight. The result is a point dataset with elevation and intensity values for every point.  LIDAR is available for download in the Digital Data Request (DDR), when specifiying what data to receive make sure the planimetrics check box is checked, and you will then have the option to request LIDAR data.

3D Elevation All Returns 3D Elevation Points 3D Elevation Bare Earth All Returns 3D Elevation Bare Earth Points

How can I use LIDAR in Autodesk Land Desktop or ArcGIS?

Click here for steps on getting started with LIDAR in Autodesk Land Desktop and ArcGIS.

When was the Johnson County LIDAR flown?

Approximately 480 square miles of new LIDAR data was captured in late December 2011  


 LIDAR flight map

Johnson County LIDAR Specifications

LIDAR data was captured at a nominal post spacing of 1.0 meter (3.2 feet) and tiled into 5,000 X 5,000 feet tiles. First, Middle and Last returns were delivered in LAS files.

Filtering to bare earth should meet the following standards:

  • 90% of artifacts removed.
  • 95% of outliers removed.
  • 95% of vegetation removed.
  • 98% of buildings removed.

Data Accuracy

The bare earth data shall have the following root mean squared errors (RMSE’s) relative to North American Vertical Datum 1988 (NAVD88) and be able to support 2-foot contours (meets both USGS and FEMA specifications):

  • Vertical bare earth 18.74 cm (0.615 ft) Root mean squared error (RMS) @ 95% confidence.
  • Vertical in vegetation 25.633 cm (0.841 ft) RMS @ 95% confidence.
  • Horizontal less than 1 meter (or 2.6 feet) RMS @ 95% confidence.

What Format is the Data in?

Johnson County received the data in LAS format which is a binary file that is becoming the industry standard. Johnson County redistributes the data in .las and .xyz format for ease of use. In addition, a geotiff(.tif) of the DEM displays the data in rasterized format. If you are interested in software that will read LAS files reference the "Where can I learn more?" section. If you have questions about any of the data formats please let us know by contacting the mapper of the day.

What types of applications is LIDAR data used for?

The most common use of LiDAR data is to create a Digital Elevation Model (DEM). This DEM can be used for floodplain delineation and mapping, aerial photography orthorectification, breakline generation and contouring. Other uses being investigated are identification of changed areas for building and vegetation updates.

How large is the data?

There are 2 ways to measure the size of the data (disk space required and number of points). A typical 5,000 foot tile has around 3.3 million points and is about 100 megabytes in size. We are estimating that we have about 2 billion points for the entire county (55 gigabytes). Typically it isn't the file size of the data that is the problem, but instead it is the sheer number of points which is overwhelming. This is the reason the data is in a tiled format.

What future plans does Johnson County have for LIDAR?

The current flight updates the LIDAR data last collected in 2006. We will continue to evaluate how useful it is and value your feedback. Please let us know if you find it useful by contacting the mapper of the day.

Where can I learn more?

Reference

Software