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 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 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 718383.51 3251637.59 NE 724451.41 3251756.17 SE 724588.51 3244828.39 SW 718516.89 3244709.98The 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 718387.84 3251460.14 NE 724455.87 3251578.71 SE 724592.96 3244651.20 SW 718521.22 3244532.78Because 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 718074.00 3252081.00The 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 718087.56 3251879.22The 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:
c2909043_nws_50.mtd - this metadata in mp (metadata parser) compatible ASCII text form
c2909043_nws_50.html - this metadata in HTML form
c2909043_nws_50_faq.html - this metadata presented as Questions and Answers
c2909043_nws_50.sgml - this metadata in SGML form
<URL:c2909043_nws_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:
c2909043_nws_50.sid - image in 50:1 compressed MrSID form c2909043_nws_50.sdw - world file for image
Conversion of the BIP imagery into GeoTIFF form does not affect the image quality or any of the other image properties that the USGS uses to evaluate image quality and accept or disapprove contractor submitted imagery. As a natural consequence of the MrSID compression process, which is lossy, some degradation of image detail occurs on conversion to MrSID compressed form. However, the effect is acceptable for most uses at a 50:1 compression level. Because the compression is lossy, conversion of a MrSID compressed image back to a TIFF format file of much larger size does not at the same time restore all the detail present in the original BIP imagery.
The root mean square error (RMSE) of the parent BIP orthophoto for this particular image is 0.83 meters.
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 19980223 'NAPP 10823 160'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.
These data have been developed from the best available sources. Although efforts have been made to ensure that the data are accurate and reliable, errors and variable conditions originating from physical sources used to develop the data may be reflected in the data supplied. Users must be aware of these conditions and bear responsibility for the appropriate use of the information with respect to possible errors, scale, resolution, rectification, positional accuracy, development methodology, time period, environmental and climatic conditions and other circumstances specific to these data. The user is responsible for understanding the accuracy limitations of the data provided herein. The burden for determining fitness for use lies entirely with the user. The user should refer to the accompanying metadata notes for a description of the data and data development procedures.
Although these data have been processed successfully on computers at the LOSCO, no guarantee, expressed or implied, is made by LOSCO regarding the use of these data on any other system, nor does the act of distribution constitute or imply any such warranty. Distribution of these data is intended for information purposes and should not be considered authoritative for navigational, engineering, legal and other site-specific uses.