-------- Original Message --------
Subject:        RE: Aerial Photos Scanning Parameters Question
Date:   Wed, 27 Aug 2008 14:33:43 -0500
From:   David C. Clark <[log in to unmask]>
To:     <[log in to unmask]>
CC:     Xiaohong Zhang <[log in to unmask]>
References:     <[log in to unmask]>



Hi, I’m working with Xiaohong on this project, and I’d like to make a
clarification on what our objectives are. Her original post stated that
we would like:

   1. To create a digital archive of this unique resource;
   2. To have the digital files serve as the source of our prints so
      that we are no longer sending out the mylars; and
   3. To create a geo-referenced “mosaic” of each year’s imagery for use
      with GIS mapping software (i.e. ArcMap or ArcIMS).

These mylar sheets are custom enlargements produced for CMAP’s
predecessor, the Northeastern Illinois Planning Commission. These sheets
contain not only the 1” = 400’ image, but location information
(political township and PLS town/range/section), scale bar, photograph
date and the logo of the company that did the photography (mostly, but
not exclusively, Geonex/Chicago Aerial Survey).

To this date, people are still requesting copies of this imagery; not
only the latest edition (2001), but the older images going back to 1970.
Until recently we fulfilled these requests by sending the mylars out to
a reproduction company that would make prints using the diazo process.
As most of you are probably aware, diazo has fallen out of fashion and
fewer and fewer companies are offering that service. The reproduction
company we currently work with sends the mylars through a high-speed
scanner, outputting a laser print which is inferior in quality to the
diazo prints.

Even though these mylars are enlargements of the original aerial
photography, they are considered by CMAP as an agency record worthy of
archiving (objective 1). Since the repro shops now scan the mylars to
fill our orders, we would like to send our (hopefully) higher-quality
scans to them for printing, thus reducing wear and tear on our already
scratched-and-creased mylars (objective 2). Since we would then have the
imagery in TIFF format, we thought that it would be nice to have a
georeferenced mosaic of the imagery (objective 3), recognizing that the
resulting product would have limited usefulness. We are primarily
concerned at this point with the first two objectives, and we’d greatly
appreciate it if anybody who has been involved in a similar project
could share their experiences with us.

Thank you,

David C. Clark, Senior Analyst

Chicago Metropolitan Agency for Planning (CMAP)

233 S. Wacker Drive, Suite 800

Chicago, Illinois, 60606

phone: 312.386.8682

fax: 312.386.8683

email: [log in to unmask] <mailto:[log in to unmask]>