1992 Color-IR Orthophotos

Greyscale Orthophotos
Statewide Update
March/April 1997

John Mackenzie
( corrected images posted 6/16/99 )

Background

The State of Delaware contracted with Earth Data (formerly PhotoScience) to update the 1992 1-meter resolution color-IR digital orthophotos series for Delaware with a 1-meter resolution greyscale digital orthophoto series.  The state was re-flown in March/April, 1997.  As before, the airphotos were digitized and georeferenced to Delaware State Plane coordinates (meters, North American Datum 1983, based on GRS 1980 spheroid).  The source data are TIFF-format ~50 MB 8-bit greyscale files for each of the 172 quarter-quads in Delaware.

To disseminate these data on the web, we resampled the 172 DOQ's covering the state to 5-meter resolution without changing projection, using a nearest-neighbor (i.e. center-cell selection) resampling procecure which generates a high-contrast image with some blockiness in very small features.  Most images were brightened and contrast-enhanced using Adobe Photoshop.  To reduce file size and eliminate sun glare, large water areas are masked to black.  These files are distributed in JPEG format in the original DE State Plane (NAD83 meters) projection.  (If you want orthos in UTM NAD83 projection, use our 1992 color-IR series.)  .

The original 1992 and 1997 series have differing degrees of positional error, and thus are not perfectly congruent.  Earth Data used a larger set of ground control points to geo-reference the 1997 series, so these should have better positional acuracy.

To view any quarter quad, simply click inside any highlighted quarter quad in the reference map to view (download) an image.  Or you can select from the alphabetical list of images.

Note that these images are larger than most monitors, so you may have to pan around a downloaded image using the horizontal and vertical display bars on edges of the image frame. To save a displayed image to your disk, click your right mouse button on it, select "Save Image As" and give the image any name you like. Netscape Navigator will save the displayed image in JPEG format; Internet Explorer will save it in Windows Bitmpa (BMP) format. Saved as BMP's, these will be very large files with no gain in image quality. To download and save as JPEG with Internet Explorer, right-click on the link in the alphabetical list, not the displayed image itself.

Alphabetical list of JPEG-format DOQ's


Importing DOQ images into ArcView

To import these data into a GIS, you will need to save a copy of the appropriate header information for each DOQ image you
download. As noted above, these are DE State Plane (NAD 1983 meters) projection. Cell resolution is exactly 5 x 5 meters.

Here are suggestions for importing these data to various GIS's:

We would appreciate your comments or suggestions!

Files copyright J. Mackenzie, 1999.
We disclaim any and all liability resulting from any errors in these data.


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