DVD discs containing Digital Terrain Models (DTM) and LiDAR data for Lake County are now available for purchase. The DTMs were developed using LiDAR data. LiDAR is an acronym for LIght Detection And Ranging. Light detection and ranging is the science of using a laser to measure distances to specific points. A specially equipped airplane with positioning tools and LiDAR technology was used to measure the distance to the surface of the earth to determine ground elevation. The classified points were developed using data collected in April - May 2007. The LiDAR points, specialized software, and technology provide the ability to create a high precision three-dimensional digital elevation and/or terrain models (DEM/DTM). The use of LiDAR significantly reduces the cost for developing this information.
The DTMs are intended to correspond to the orthometric heights of the bare surface of the county (no buildings or vegetation cover). DTM data is used by county agencies to study drainage issues such as flooding and erosion; contour generation; slope and aspect; and hill shade images.
Customers interested in the actual classified LiDAR point data may download it at no cost from the USGS Center for LiDAR Information Coordination and Knowledge.
These data were compiled to meet the American Society for Photogrammetry and Remote Sensing (ASPRS) Accuracy Standards for Large-Scale Maps, CLASS 1 map accuracy.
The U.S. Army Corps of Engineers Engineering and Design Manual for Photogrammetric Production recommends that data intended for this usage scale be used for any of the following purposes: route location, preliminary alignment and design, preliminary project planning, hydraulic sections, rough earthwork estimates, or high-gradient terrain / low unit cost earthwork excavation estimates. The manual does not recommend that these data be used for final design, excavation and grading plans, earthwork computations for bid estimates or contract measurement and payment.
This data does not take the place of an on-site survey for design, construction or regulatory purposes.
Each DVD contains individual DTM data files in ERDAS .img format, LiDAR data in LAS file format and breaklines in Esri shapefile format. The tile scheme used for the DTM is based on the approximate Public Land Survey System (PLSS) section lines, covering approximately one square mile. They are not based on Public Land Survey System monument coordinates. Consult a professional Land Surveyor registered to practice in Illinois if true ground locations are needed.
The files provided are in the Illinois State Plane Projection, East Zone, and the HARN Horizontal Datum. The vertical datum is NAVD88. The units of measure are US Survey feet. Each DVD also includes metadata compliant with Federal Geographic Data Committee metadata standards.
Purchasers should verify that the software they plan to use with this data is capable of reading this DTM sample IMG file before buying the DVD.
The Spring 2007 Classified LiDAR point data (LAS format) from which the DTMs were derived is included with this DVD. Purchasers should try this sample LAS file before buying the DVD.
The price for each DTM data DVD is $50 per PLSS township and includes: the individual PLSS section IMG files for that PLSS township; corresponding PLSS section Classified LiDAR points (.las) for that PLSS township; 3D breakline data (.shp) for the entire county; and a GIS index / tile scheme dataset (.shp) for the entire county.
The purchase price is not refundable. A defective disc may be exchanged for a replacement disc for the same product at no charge. Purchasers should verify that the software they plan to use with this data is capable of reading the sample files available above. No software is provided with the data on these DVDs.
The Spring 2007 digital orthophoto obtained in the same period as the LiDAR data is available on DVD and makes an excellent companion to the DTM data. Although the DTM data can be viewed with earlier or later digital aerial photography the surface of the land will not precisely match the DTM due to such factors as new construction, demolition, road alignment changes, lake and stream erosion or restoration projects and other events. There is a high rate of change in the landscape in many parts of Lake County that may alter the elevation of the land.
Information about digital aerial photography available from the county may be found here.
The Spring 2007 1 Foot Cartographic Contours, which were derived from the 2007 Classified LiDAR point cloud, are also available. Further information about the 2007 1 Foot Cartographic Contours may be found here.