| Category |
Land Base Data |
| Name(s) |
ft.5-93 ft1-93 ft2-93 ft4-93 ft8-93 |
| Description |
Digital Orthophoto Images (April 1993) |
| 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 Othophotos. Layers ftx-93 represent imagery of various resolutions acquired from the April 1993 aerial photography. |
| |
|
| Maintenance |
The Large-Scale GIS Land Base Development Project created the original digital orthophotography based upon April 1993 aerial photography. |
| |
|
| Source |
Large-Scale GIS Data Base Development Project (1993) |
| |
|
| 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 |
Large-Scale GIS Data Base Development Project Areas, 48.6 Square Miles |
| Format |
256 gray scale, image (.jpg) and World File (.jgw) file pairs. |
| Count |
See Qualifications Table |
| |
|
| Qualifications |
The April 1993 black and white aerial photography used for production of the digital orthophotography has a photo scale of 1:7680 or 1"=640' with 80% forward lap and 48% 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 as .tif |
| ft.5-93 |
6" pixels |
a |
1,000' by 1,500' |
884 |
5304 MB+ |
| ft1-93 |
1' pixels |
b |
2,000' by 3,000' |
221 |
1326 MB+ |
| ft2-93 |
2' pixels |
c |
4,000' by 6,000' |
67 |
402 MB+ |
| ft4-93 |
4' pixels |
d |
8,000' by 12,000' |
23 |
138 MB+ |
| ft8-93 |
8' pixels |
e |
16,000' by 24,000' |
6 |
36 MB+ |
The aerial photography diapositives were scanned at 15 microns (1,693 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 references to individual image files for use with ArcInfo and ArcView software. Image 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 (.jgw) stores information regarding the real world coordinate positioning of the .jpg image file. |
