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2002 Digital Orthophotos

Category Land Base Data
Name(s) ft.5 ft1 ft2 ft4 ft8 ft16
Description Digital Orthophoto Images (April 2002)
Type Image Catalogs
   
Abstract Digital Orthophotography is the major component of the Land Base for the Ann Arbor Geographic Information System. All existing features that appear on the aerial photography at a given scale are shown in the Digital Orthophotos. Layers ftx represent imagery of various resolutions acquired from the April 2002 aerial photography.
   
Maintenance The 2002 Digital Orthophoto Update Project created additional digital orthophotography based upon April 2002 aerial imagery to supplement the original digital orthophotography from April 1993 and subsequently from April 1997. Future plans include exploring new production methods and funding sources.
   
Source Digital Orthophoto  Update Project (2002)
   
Agency/Contact Information Technology Services Department / mjohnson@ci.ann-arbor.mi.us
   
Accuracy National Map Accuracy Standards for 1"=100', 1-2 foot positional accuracy
Projection NAD83 State Plane, Michigan South Zone 6401
Units US Survey Feet
Spheroid GRS1980
   
Domain Entire area of Washtenaw County plus 1 mile buffer
Format 256 gray scale, Uncompressed TIFF image (.tif) and World File (.tfw) Pairs, each pair approximately 6 MB
Count See Qualifications Table
   
Qualifications The April 1997 black and white aerial photography used for production of the digital orthophotography has a photo scale of 1:7680 or 1"=640' with 60% forward lap and 65% side lap on Agfa Pan 50 film. The 9"x9" contact prints are on file with the Planning Department.

Airborne GPS technology along with control panels on the ground were used in the aerial mission with an altitude of 3,840 feet. The character of aerial photography is preserved in digital orthophotography including the radial displacement of tall structures away from the center of each photo. Correction of distortion at ground level due to the camera lenses and surface terrain meet National Map Accuracy Standards as stated above.

Qualifications
Image Catalog Resolution Class Dimensions Count Storage
ft.5 6" pixels a 1,000' by 1,500' 953 5718 MB+
ft1 1' pixels b 2,000' by 3,000' 245 1470 MB+
ft2 2' pixels c 4,000' by 6,000' 72 432 MB+
ft4 4' pixels d 8,000' by 12,000' 23 138 MB+
ft8 8' pixels e 16,000' by 24,000' 6 36 MB+
ft16 16' pixels f 48,000' by 48,000' 1 9 MB+

The aerial photography diapositives were scanned at 12 microns (2,000 dpi).The 6-inch pixel resolution primary digital orthophotography was then resampled to create the successively larger resolution imagery.

Image catalogs are INFO tables which contain geographic reference to individual image files for use with ArcInfo and ArcView software. Images files making up the image catalogs can be accessed and/or used independently. Naming of the individual image files reflects the resolution of the image and the location of the lower-left corner in State Plane coordinates (feet). For example, an image named b2950288.tif represents an image with 1-foot pixel resolution and a lower-left corner at the State Plane x = 13,295,000 and y = 288,000.

The World File (.tfw) stores information regarding the real world coordinate for positioning of the TIFF image file.