The Will County, IL lidar project area covers approximately 887 square miles. The lidar data was acquired at an aggregate nominal point density (ANPD) of 10. Project specifications are based on Will County requirements. The data was developed based on a horizontal projection/datum of NAD83(2011) / Illinois State Plane East Zone (ftUS) (EPSG Code: 3435), and vertical datum of NAVD88 - Geoid12B (US Survey Feet)--ISGS comment: all the data uses Geoid 18--. LiDAR data was acquired using a Optech Galaxy T2000 sensor from March 29, 2021 to April, 13, 2021 in 8 total lifts. Acquisition occurred with leaves absent from deciduous trees, when no snow was present on the ground, and with rivers at or below normal levels. Note: ISGS QAQC review found that there are numerous noise points on the DSM, making that DSM unusable in some areas.

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Ayres Associates utilized these DTM components to generate the contours using the following procedures: Ayres methodology incorporates bare earth model keypoints and the hydro breaklines to create the contours. Model keypoints are a subset of bare earth points that are extracted from the full resolution point cloud using an intelligent data decimation algorithm. This algorithm works by thinning out the data in areas of little relief while keeping more points near breaks and in areas of greater variation in terrain. This process results in more manageable file sizes for TIN generation and a more cartographic appearance to the contour dataset.

All contours products were produced using Terrasolid’s TerraModeler software. TerraModeler is a full-featured terrain modeling application that incorporates intelligent filtering and smoothing algorithms for contour generation. The contours were generated from a TIN model created using the model keypoints and breaklines. Ayres employed this software’s recommended parameters and model keypoints with 20-ft spacing to create a more cartographically smoothed contour data. Additionally, Ayres filtered out enclosed contour polygons on hills and depressions that are 100-ft in circumference or less as a means of reducing file size and improving cartographic readability of the contours.

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Continuous 2-ft contours were generated for Will County Illinois according to FEMA specifications using LiDAR data.

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