This color infrared orthophoto was created from color infrared aerial photography film. Color infrared film is manufactured to be sensitive to red, green and near-infrared wavelengths. This type of film makes near-infrared reflected energy visible to the human viewer by capturing that energy and representing it as a visible color. The dyes that are used in the film render green objects as blue images, red objects as green images, and objects that primarily reflect infrared as red images. Because healthy vegetation reflects strongly in the near infrared, areas of vegetation appear red or pink. The appearance color for water in CIR imagery is highly variable and dependent on the depth and amounts of floating vegetation and suspended matter. It can range in color from olive drab through turquoise, deep blue and to black. Barren areas can be highly reflective at all wavelengths, thus frequently appear very bright in a CIR image.
This image has an overedge of approximately 300 meters on all sides, so the area encompassed is actually somewhat larger than 3.75 minutes by 3.75 minutes. Each pixel in these orthophotos represents an area of one square meter on the ground.
The image is in Multi-Resolution Seamless Image Database (MrSID) form. Like the other common photographic image compression methodology, JPEG, MrSID compression maintains high visual image quality even at high compression levels. The advantages MrSID offers over JPEG is a faster display rate and a 'smooth' appearing image at any magnification level, the latter being a manifestation of the 'Multi-Resolution' qualities of this imagery. The compression levels obtained make it possible to distribute this MrSID imagery over the web, even to users with modem-only access to the Internet, and to put a hundred or more MrSID orthos on a single CD-ROM. Imagery in MrSID form is supported in most major GIS software. It can also be manipulated in Adobe Photoshop or viewed, subset, and converted to standard TIFF format imagery with a free stand-alone viewer available from LizardTech (<URL:http://www.lizardtech.com>).
The primary datum tics (13 by 13 pixel solid white crosses) have the following ground coordinate values in UTM Zone 15 NAD83 coordinates:
corner easting northing NW 767419.23 3231890.50 NE 773499.49 3232034.55 SE 773665.33 3225105.51 SW 767581.37 3224961.65The secondary datum tics (13 by 13 pixel dashed white crosses) have the following ground coordinate values in UTM Zone 15 NAD27 coordinates:
corner easting northing NW 767424.51 3231713.84 NE 773504.89 3231857.89 SE 773670.72 3224929.11 SW 767586.65 3224785.25Because of the image detail that is lost when full-detail source DOQ imagery is compressed, the tics no longer appear as solid white crosses or dashed white crosses in the MrSID compressed imagery. Nonetheless, the primary datum tic can be differentiated from the secondary datum tic because the former appears brighter and whiter than the latter.
The ground coordinates of the upper left hand corner of the upper left hand pixel in primary datum (UTM zone 15 NAD83) coordinates are:
easting northing 767111.00 3232360.00The ground coordinates of the upper left hand corner of the upper left hand pixel in secondary datum (UTM zone 15 NAD27) coordinates are:
easting northing 767124.55 3232158.23The metadata for this image are encapsulated into several documents. The metadata are not complete if you did not receive the following files along with the data set:
c2909055_sws_50.mtd - this metadata in mp (metadata parser) compatible ASCII text form
c2909055_sws_50.html - this metadata in HTML form
c2909055_sws_50_faq.html - this metadata presented as Questions and Answers
c2909055_sws_50.sgml - this metadata in SGML form
<URL:c2909055_sws_50.hed> - the first 50-60 lines of the source ortho header. This information
may be more easily parsed than these metadata if further automated
processing of the imagery is desired.
The image is accompanied by a georeferencing 'world' file. Following
the ArcView / ArcInfo convention for such files, the xy origin specified
in this file refers to the center of the upper left hand pixel of the image.
You should have received the following as part of the dataset:
c2909055_sws_50.sid - image in 50:1 compressed MrSID form c2909055_sws_50.sdw - world file for image
Louisiana Oil Spill Coordinator's Office (LOSCO), 19990608, Color Infrared Orthophoto, SW quadrant of Leeville Quadrangle, LA, 50:1 MrSID compressed, LOSCO (1999) [c2909055_sws_50].
This is a raster data set. It contains the following raster data types:
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 1.0
Ordinates (y-coordinates) are specified to the nearest 1.0
Planar coordinates are specified in Meters
The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 80.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257.
Louisiana Oil Spill Coordinator's Office
c/o David Gisclair
Technical Assistance Program (TAP) Director
Louisiana Oil Spill Coordinator's Office
Baton Rouge, LA 70804
(225) 219-5800 (voice)
(225) 219-5802 (FAX)
<URL:mailto:tapgis@linknet.idt.net>
Color infrared orthophotography serves a variety of purposes. It is commonly used as a backdrop for sparse vector data in a GIS. It may be used as a source for photointerpretation of features or for on-screen digitizing of the positions, paths, and boundaries of recognizable features such as oil storage tanks, roads, and buildings.The user should be aware that adjacent orthophotos were produced from imagery with different center points. Because the orthophoto production process only corrects features at the ground level, the tops of buildings and other structures elevated above the surface of the ground 'lean' or 'tilt' away from the center point of the source photography and from their own bases. Adjacent orthophotos share common area because of the 'overedge' on each image. In these shared areas, the 'lean' direction of elevated objects will be different for the adjacent orthophotos because their source photography had different center points. For the purposes of photointerpretation of the locations of elevated objects visible in orthophotography, the user should select a point at the base of the elevated object rather than at its top. This convention will insure that the object location point appears at the base of the elevated feature, independent of which orthophoto is displayed as a backdrop. A point selected at the top of an elevated object in one orthophoto will very likely not fall at the top of the same elevated object in the adjacent orthophoto. Furthermore, the xy coordinates of a 'top point' so selected are neither the coordinates of the top of the object in the real world nor its base because of the 'lean' displacement in the orthophoto caused by the non-compensated height of the elevated object.
The BIP orthophoto was created from a digital elevation model (DEM) dated 19990101 and the aerial photo(s) listed below using 'Carl Zeiss PHODIS on SGI' software and hardware:
date Image ID 19980204 'NAPP 10810 52'A DEM source date like this one, 19990101, ending in '0101' is a 'flag date,' of sorts. Any DEM source date ending in '0101' means that either the DEM source day within the month of January was unknown or, more likely, neither the month nor the day within the year 1999 for the production of the DEM is known. Thus, the particular DEM under consideration may have been produced at any time within the 1999 year. However, many DEMs produced earlier than 1993 had no source date information. In that situation, the procedure is to write a DEM_SOURCE_DATE in the DOQ header composed from the year of ortho production, '01' for the month, and '01' for the day. This DEM source fits that picture and hence, in addition to the possibility of being produced at any time during the 1999 year, the DEM may have been produced at some unknown date prior to 1993.
Person responsible for change:
3001, Inc.
c/o Kevin Hanzo
Department Manager, Orthorectification
5525 Mounes, Suite 102
New Orleans, LA 70123
(504) 733-3001 (voice)
<URL:mailto:khanzo@3001data.com>
Person responsible for change:
3001, Inc.
3655 SW 2nd Ave., Suite 3C
Gainesville, FL 32607
(352) 379-3001 (voice)
Person responsible for change:
3001, Inc.
c/o Mendi Johnson
GIS Analyst
3655 SW 2nd Ave., Suite 3C
Gainesville, FL 32607
(352) 379-3001 (voice)
<URL:mailto:mjohnson@gnv.3001data.com>
In order to be approved by the USGS, a certain number of orthophotos are checked to insure that they meet National Map Accuracy Standards for this product. Digital data like these have no inherent scale, but for purposes of testing, 3.75 minute digital orthophotos are evaluated as if they were a paper map published at 1:12000 scale. The criteria for these orthophotos is then that 'not more than 10 percent of the points tested shall be in error by more than 1/30 inch, measured on the publication scale.' At the 'scale' of this product, that can be translated to: 'not more than 10 percent of the points tested shall be in error by more than 33 feet (as measured on the ground and using other higher accuracy data as positional reference)'.
The root mean square error (RMSE) of the parent BIP orthophoto for this particular image is 1.48 meters.
The image has an overedge of approximately 300 meters on all sides of the nominal 3.75 minute cell this image is meant to cover.