| 2008 Aerial Photography | |
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Data format: SDE Raster Dataset File or table name: RASTER.LIBRARIAN.IMAGES08 Coordinate system: Transverse Mercator Theme keywords: Aerial image, ADS40, Basemap, Digital orthophoto, Orthophoto |
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Abstract:
This metadata describes the digital ortho imagery for Lake County, FL. This 1":100' scale imagery is comprised of natural color orthophotography with a GSD (Ground Sample Distance) of 0.5'. Imagery was collected with the Leica ADS40 digital sensor and processed with Leica GPro software. This imagery is projected in NAD83 FL East State Plane Coordinate System feet. The original data was delivered as a complete county wide dataset and was then broken out into 6 individual areas to create smaller file sizes for download. The 6 areas were created by Lake County GIS to generate areas of similar geographic size and file size. This metadata reflects that of the originally delivered data. |
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Metadata elements shown with blue text are defined in the Federal Geographic Data Committee's (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM). Elements shown with green text are defined in the ESRI Profile of the CSDGM. Elements shown with a green asterisk (*) will be automatically updated by ArcCatalog. ArcCatalog adds hints indicating which FGDC elements are mandatory; these are shown with gray text.
This metadata describes the digital ortho imagery for Lake County, FL. This 1":100' scale imagery is comprised of natural color orthophotography with a GSD (Ground Sample Distance) of 0.5'. Imagery was collected with the Leica ADS40 digital sensor and processed with Leica GPro software. This imagery is projected in NAD83 FL East State Plane Coordinate System feet. The original data was delivered as a complete county wide dataset and was then broken out into 6 individual areas to create smaller file sizes for download. The 6 areas were created by Lake County GIS to generate areas of similar geographic size and file size. This metadata reflects that of the originally delivered data.
A digital orthophoto is a geometrically accurate photographic record of landscape conditions at the time of the corresponding aerial photography. As such, the digital orthophoto is useful for a variety of applications, such as environmental monitoring, facility engineering/maintenance, city/county planning, property line review, etc. The digital orthophoto can be used alone or as a raster basemap for corresponding vector line mapping.
The bounding coordinates in this metadata file represent the bounding coordinates for all image tiles in project area as a whole, not an individual tile.
ground condition
None
317 West Main Street, Historic Courthouse, 4th Floor
Compliance with the accuracy standard was ensured by the placement of GPS ground control prior to the acquisition of aerial imagery. The following checks were performed: 1. The ground control and airborne GPS/INS data stream were validated through an aerotriangulation bundle adjustment using Leica's ORIMA and CAP-A software. The residuals of the adjustment met the required standards with the results fully outlined in an AT report. 2. Digital orthophotography was validated through a visual inspection of control points, edge matching and general image quality.
The following methods were used to ensure image quality: 1. Use of targeted ground control during image acquisition. 2. Use of GPS/INS during image acquisition. 3. Checking of controls against ortho product. 4. Post ortho accuracy approval checks for overall image quality (tone, color balance, etc.).
This image complies with NMAS standards. It has been tested at 95% confidence level to have an RMS positional displacement within 3' of well defined ground features in obscured areas. Does not apply to vertical surface features, such as structures, appearing in the digital orthophotography due to inherent lean. Tested horizontal RMSE on controls within the project area is 0.6'.
There is no vertical component for orthos.
The aerial imagery was captured with a Leica Geosystems ADS40 digital camera. The ADS40 uses a 'pushbroom' method of data collection with different sensors using forward, rearward and nadir orientations along planned flightlines. This results in one image per sensor for each flightline. The aerial images are used to AT the project and the production of orthophotos.
Targeted ground control is used to create a digital control file and control report as well as QC check of ortho accuracy. Predefined points (usually NGS) within the county are targeted, making the points visible in the photography. These points along with their precise coordinates are used in the AT process and to check the horizontal accuracy of the resulting orthophotos. 103 control points were used for this project.
This project used existing LiDAR-derived DEM data. The DEM is used in the orthophoto production process.
The tile definition is used to cut orthorectified imagery into manageable, usable images. Each tile is 5000' X 5000'.
This first level of orthorectified images are the product of using the AT solution and the DEM in GPRO. They are large 4GB swaths that have yet to be mosaicked into manageable tiled orthos.
The tiled orthophoto is the result of mosaicking orthorectified imagery and using the tile definition to cut into manageable, usable orthophotos.
At selected locations throughout the site, accurate GPS coordinates and elevations are surveyed and the points are marked with targets which will be visible in the aerial photography.
New digital, color aerial imagery of the site is acquired using the Leica ADS40 camera. Airborne GPS/IMU data is recorded along with the imagery
Imagery and GPS/IMU data is downloaded from disc on the plane to disc on the ground. GPS/IMU mission data is processed together with simultaneously collected ground-based GPS base station data in forward and reverse directions. This precisely determines the aerial camera's position and orientation in the terrain (project) coordinate system and allows for correct orientation of the imagery.
Using the processed GPS/IMU data and correctly oriented imagery, a bundle adjustment is computed (AT) in Leica Geosystems ORIMA/CAP-A software.
Orthorectified imagery is produced using Leica Geosystems GPRO software. They are large 4GB swaths that have yet to be mosaicked into manageable tiled orthos.
Orthorectified imagery is mosaicked, locally color-balanced and cut to the tile definition boundaries using Stellacore OrthoVista software. The tiled orthos are checked for accuracy against the surveyed ground control before further image editing.
Tiled orthophotos then go through a rigorous manual QC process to evaluate for remaining hotspots (sun reflectance over water), tone quality, color balance and the feathering area between flightlines. Any imperfections at this point are manually edited. If necessary, the tiled images are then converted to required format. All images are either recorded on DVD, transferred to HD or posted on FTP for client access.
Color orthophotos are comprised of pixels. Each pixel is assigned a value of 0 to 255. That number will refer to a color look-up table which contains red, green and blue (RGB) values, each from 0 to 255, for that pixel within the image.
None
317 West Main Street, Historic Courthouse, 4th Floor
Lake County, FL provides the geographic data "as is". This organization makes no guarantee or warranty concerning the accuracy of information contained in the geographic data. Also, this organization makes no warranty, either expressed or implied, regarding the condition of the product or its fitness for any particular purpose. The burden for determining fitness for use lies entirely with the user. Although these files have been processed successfully on computers at this organization, no warranty is made by this organization regarding the use of these data on any other system, nor does the fact of distribution constitute or imply such a warranty.
Download from ftp://ftp.co.lake.fl.us/GIS/GisDownloads/Imagery/2008/ by individual areas
317 West Main Street, Historic Courthouse, 4th Floor