An orthoimage is remotely sensed image data in which displacement of features in the image caused by terrain relief and sensor orientation have been mathematically removed. Orthoimagery combines the image characteristics of a photograph with the geometric qualities of a map. For this dataset, the natural color orthoimages were produced at 0.3-meter pixel resolution (approximately 1-foot). The design accuracy is estimated not to exceed 3-meter diagonal RMSE (2.12m RMSE in X or Y). Each orthoimage provides imagery for a 1500- by 1500-meter block on the ground. The projected coordinate system is UTM with a NAD83 datum. There is no image overlap been adjacent files. The naming convention is based on the U.S. National Grid (USNG), taking the coordinates of the SW corner of the orthoimage. Note: MARIS has mosaiced these images to basically conform to 1:24,000 USGS quarter quad boundaries. This takes the over 700 files down to 36 files for the Jackson, MS area. The files have been compressed with MrSID at a 20:1 compression ratio.
These data have been created as a result of the need for having geospatial data immediately available and easily accessible in order to enhance the capability of Federal, State, and local emergency responders, as well as plan for homeland security efforts.
This is a collection-level metadata record created for the Jackson-area high resolution orthoimagery. Therefore the bounding coordinates are not specific to individual quarter-quad tiles.
ground condition
None. Acknowledgment of the U.S. Geological Survey would be appreciated for products derived from these data.
During photographic reproduction of the source photographs, limited analog dodging (radiometric editing) is performed to improve image quality. Analog dodging consists of holding back light from certain areas of the sensitized photographic material to avoid overexposure. The diapositive is inspected to ensure clarity and radiometric uniformity. Diapositive image brightness values are collected with a minimum of image quality manipulation. Image brightness values may deviate from the brightness values of the original images because of image value interpolation during the scanning and rectification processes. Radiometry is verified by visual inspection of the digital orthophoto with the original unrectified image to determine if the digital orthophoto has the same or better image quality as the original unrectified input image. Slight systematic radiometric differences can be detected between adjacent orthoimage files; these are due primarily to differences in source photograph capture dates and sun angles along flight lines when the aerial photographs were taken. These differences can be observed in an image's general lightness or darkness when it is compared to adjacent orthoimage file coverages. Tonal balancing may be performed over a group of images during the mosaicking process which may serve to lighten or darken adjacent images for better color tone matching.
The horizontal positional accuracy and the assurance of that accuracy depend, in part, on the accuracy of the data inputs to the rectification process. The location of photoidentifiable test points were evaluated on the Geotiff image and compared with their ground values in order to determine an overall accuracy for each test block of orthoimages within the project. After image coordinate measurement was completed for each block, an RMSE for the diagonal error was calculated for the orthoimages within the block. This value is an estimate of the horizontal accuracy of the tile expressed in meters.
Field GPS Ground-Truth Comparison Procedure. Internal Documentation: Jackson, MS Field GPS Ground-Truth Comparison Report.
Provides the imagery for the digital orthoimage.
Provides the imagery for the digital orthoimage.
Provides the imagery for the digital orthoimage.
USGS format elevation data with a 30m grid post interval. Used to provide ground elevations for orthorectification process.
Horizontal and vertical control used to establish positions and elevations for reference and correlation purposes and as input to the aerotriangulation process. Control consists of both Airborne GPS to provide camera station positions and photoidentifiable surveyed ground control for ground reference.
The aerial platform used during the photo acquisition for this project was a Rockwell Turbo Commander turbine-powered aircraft capable of cruise speeds of around 215 knots. This capability is very important for good production on a very large photo acquisition project such as this one. A Jena LMK 2000 lens high-precision photo-grammetric camera was used as the photographic instrument. This camera has a nominal 6-inch focal length with Forward Motion Compensation (FMC,) gyro-stabilized mount, airborne GPS (ABGPS,) and Inertial Measurement Unit (IMU). Dual-frequency GPS observation data was collected on-board the aircraft at a one second epoch. Additionally, inertial data was collected during all periods of flight and is collected at a rate of 0.005 seconds. The midpoint of each photo exposure was precisely captured as an 'event' by the GPS receiver. All ABGPS and Inertial data was then post-processed to provide accurate positional and rotation data of the camera for each exposure. Effectively, the three dimensional position (x, y, and z) of each exposure was determined from the ABGPS data while the three-dimensional rotation (omega, phi, and kappa) of each exposure was determined from the inertial data. The IMU data (which includes adjusted position and orientation of the camera at time of exposure) were orthorectified using the relevant USGS Digital Elevation Models. These were processed using Z/I's OrthoPro package. The orthorecitifed images were then mosaicked (if necessary, to reduce the effects of micro-relief on the final product). Product tiles were then extracted from the orthorecitifed images or mosaic and converted to GeoTIFF format. Product RMS accuracy was determined by measuring the metric displacement of common features in adjacent tiles or measuring the ground control that was collected. Metadata files were then created and populated to reflect the relevant tile and project data. Product tiles and metadata were then written to DVD for delivery to USGS. Note: The individual .tif files were compressed by MARIS using LizardTech's MrSid compression. The files that formed the quarter quads were then mosaiced using Leica Imagine 8.4 to form basic quarter-quad .tif images. The final images were then compressed with 20:1 compression ratio. The files were pulled into ArcMap 9.0 where the projection nformation was added. The files were then Winzipped for distribution. Each zip file contains the .sod,.sdw,.aux, and .xml projection file for a quarter quad. There is an index map showing the file naming schema.
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