STATEMENT
OF THE PROBLEM
A key element to the realization of the potential use of remote
sensing data is ground control. If the imagery does not line up
with the data within the GIS or GPS systems then it is perceived
to be of limited value and will not be forwarded into standard operations
and decision trees within the local government.
PRESENT
SITUATION
It became apparent early within this process that the control and
monumentation currently existing within the City, County, and private
sector were not suitable for image rectification. Basically you
could not see the features used for control from the imagery.
POTENTIAL BENEFITS
The need for a consistent system of image based control for future
use in the acquisition of imagery from service providers or in compiling
new imagery in-house necessitated the development of a system of
control that would form the base of control for years to come and
allow for the seamless integration of imagery from different temporal
periods for use in such things as change detection, accurate monitoring
and inventory, etc.
TECHNICAL APPROACH
TAKEN
Ground control points were established at three intervals covering
the Columbia and Ashland area. Each control point was pre-selected
from IKONOS imagery, and then the real world location was captured
using GPS. Points were stored as latitude/longitude coordinates
in three separate files according to their time of collection. The
latitude/longitude coordinates were converted by hand into decimal
degrees in order to generate a point coverage in Arc. The coverage
was projected into State Plane (NAD 83) to coincide with the images’
projection. The point coverage was then opened in ArcEdit along
with the associated background image for a location reference. The
same image was opened in ENVI 3.2. The background images were a
combination of digital orthophoto quarter quadrangles (DOQQs) and
IKONOS imagery. The images from the DOQQs (Figure 1) are, on average,
five to ten years older than the recently taken IKONOS images (April,
2000)(Figure 2). This creates temporal discrepancies between the
two formats around rapidly urbanizing areas since the ground control
points were selected from IKONOS imagery.
Points that were visible on the DOQQs were used first, because
of the potential for registering and mosaicing the DOQQs to form
a base map. Points that were not visible on the DOQQs were selected
from the IKONOS images. A ground control point was selected in ArcEdit,
along with its approximate location in relationship to the unregistered
background image. The same location was found on the ENVI image.
With the help of diagrams (Figure 3), demarcated aerial photographs,
and hand-held digital camera images (Figure 4), the precise location
of the real world ground control point was marked on the ENVI image.
Figure 1 Site on DOQQ
Figure 2: Site on IKONOS Image
Figure 3: Site Sketch
Figure 4: Site Photograph
The image location and the real world State Plane coordinates were
saved into a ground control point file in ENVI. A large-scale image
of each ground control point was converted into a TIFF file (Figure
5) for visual referencing.
Figure 5: Small Scale Image of Site Context
The coordinates found in every ground control point file were transferred
to an Excel spreadsheet and combined into a master list. The master
list contains a unique identification number, the State Plane coordinates,
the name of the DOQQ or IKONOS image that it was taken from, and
the original GPS point name as given by the surveyor.
PRODUCTS CREATED
A digital file containing a series of image based control for the
City of Columbia, and portions of Boone County to include: a unique
identification number, the State Plane coordinates, the name of
the DOQQ and/or IKONOS image that it was taken from, the original
GPS point name as given by the surveyor, sketch map of site, up
to three photographic images of the site itself, and a site context
image.
ANTICIPATED IMPLEMENTATION
PROBLEMS IN LOCAL GOVERNMENT
Maintenance of the file and the development of a full suite of imagery
based control for the entire county will need to be pursued. Format
and conversion issues with the images and data base files should
be minimal.
ADDITIONAL WORK
Development of the full county image control base is needed to complete
the data base. The structure and design is in place and usable.
There may be user interface issues that will need to be addressed.
As well, these points need to be posted on the web site for all
to use and be made aware of their existence.
PROJECT PARTICIPANTS
Timothy L. Haithcoat, Jim Dunajcik, and Derek Smith, Geographic
Resources Center (GRC), Department of Geography, University of Missouri
under the auspices of ICREST.
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