St. Croix 2011-12 Orthographic Imagery

This file is a single ESRI raster catalog comprised of a collection of individual GeoTIFFs of the island of St. Croix (USVI). An orthographic aerial image is remotely sensed image data in which displacement of features in the image caused by terrain relief and sensor orientation have been mathematically removed. Orthographic imagery combines the image characteristics of a photograph with the geometric qualities of a map. The source imagery was obtained from January 2011 through March 2012 and used to produce orthophotos with a 0.3 meter (approximately 1 foot) ground sample distance (GSD). The raw imagery was captured at 12-bit radiometric resolution and converted to 8-bit radiometry during post processing. The imagery was captured with approximately 60% forward overlap between adjacent exposures and 30% sidelap between all adjacent flight lines utilizing both a Microsoft UltraCAM X (2011 flights) and a Z/I Imaging DMC-II 230 (2012 flights) digital sensor. The orthographic imagery is available as 4-band (RGBI) GeoTIFF formatted digital images. The projected coordinate system is State Plane Puerto Rico / US Virgin Islands (Zone 5200), NAD 83, GRS 80, Units Meters.

Original contact information:

Contact Org: U.S. Army Corps of Engineers, Jacksonville District, Geomatics Section

Phone: 904-232-2214

Email: ted.n.schall@usace.army.mil

The purpose of the project is to provide the United States Army Corps of Engineers with updated digital orthographic aerial imagery covering all of the Commonwealth of Puerto Rico and the U.S. Virgin Islands. The Corps regularly uses digital orthographic imagery to support regulatory, land management and acquisition, planning, engineering and habitat restoration projects. The data may also become available to local, state and other federal agencies for their specific management and analysis needs.

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The data design specifications for this product includes several directed to insure its quality, consistency, and usability. These specifications address some of the technical issues associated with orthoimage production: 1) the tops of buildings and other structures elevated above the surface of the ground 'tilt' away from the center point of the source imagery and from their own bases as a result of perspective and their height which is not compensated for in digital elevation models of the ground surface and 2) individual orthoimages may be assembled from several source aerial images.

Users must assume responsibility to determine the usability of these data.

None

Acknowledgment of the United States Army Corps of Engineers would be appreciated for products derived from these data.

Microsoft Windows 7 Version 6.1 (Build 7601) Service Pack 1; ESRI ArcGIS 10.0.3.3600

Horizontal positional accuracy of the set of orthographic images was determined by comparing the positions of ten well defined points within the orthographic imagery to their corresponding field positions as determined by GPS positioning methods. The comparison of the ortho and field collected data resulted in the determination of the following statistics: Horizontal Root Mean Square Error (RMSEh) = 0.34 meters; Horizontal Standard Deviation (Sh) = 0.13 meters; National Standard for Spatial Data Accuracy Circular Error (NSSDAcircular) = 0.59 meters.; Quantitative Value: 0.59 meters, Test that produced the value: Horizontal positional accuracy of the set of orthographic images was determined by comparing the positions of ten well defined points within the orthographic imagery to their corresponding field positions as determined by GPS positioning methods. The comparison of the ortho and field collected data resulted in the determination of the following statistics: Horizontal Root Mean Square Error (RMSEh) = 0.34 meters; Horizontal Standard Deviation (Sh) = 0.13 meters; National Standard for Spatial Data Accuracy Circular Error (NSSDAcircular) = 0.59 meters.

These data cover all of the islands of the US Virgin Islands. These specifications address some of the technical issues associated with orthoimage production: 1) the tops of buildings and other structures elevated above the surface of the ground 'tilt' away from the center point of the source imagery and from their own bases as a result of perspective and their height which is not compensated for in digital elevation models of the ground surface and 2) individual orthoimages may be assembled from several source aerial images.

These specifications address some of the technical issues associated with orthoimage production: 1) the tops of buildings and other structures elevated above the surface of the ground 'tilt' away from the center point of the source imagery and from their own bases as a result of perspective and their height which is not compensated for in digital elevation models of the ground surface and 2) individual orthoimages may be assembled from several source aerial images.