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PHOTOGRAMMETRIC
WORKFLOWS
Traditional, Digital and the Future
Ryan Strynatka
Product Manager,
Leica Geosystems Geospatial
Imaging, USA.
Abstract
With the growing proliferation of “new” technologies
such a LIDAR, pushbroom, and satellite sensors, many commercial vendors have begun to
re-examine the application tools they offer.In addition, advances in information technology have opened
up the possibility of processing increasingly large quantities of data. Coupled with improved processing capabilities and network bandwidth, this is causing change in traditional photogrammetric
workflows.
TRADITIONAL PHOTOGRAMMETRIC WORKFLOWS
When asked about the “photogrammetric workflow”, most industry professionals refer to the analog frame camera (e.g.
Leica RC30) workflow. Analog frame cameras were prevalent during the transition to digital photogrammetry and remain a common source of imagery. Numerous software tools have been developed to guide users through the traditional analog frame workflow. Vendors include BAE Systems, INPHO (now a part of Trimble Spatial Imaging), Intergraph, and Leica Geosystems.
The mainstream analog frame workflow is listed below:
- Scanning process: Airborne camera film is scanned and converted
into a digital file format. Some high performance scanners
also perform Interior Orientation (IO).
- Image Dodging: Scanning may introduce radiometric problems
such as hotspots (bright areas) and vignetting (dark corners).
These can be minimized or reduced by applying a dodging algorithm.
Dodging, in the digital photogrammetry sense of the word,
generally calculates a set of input statistics describing the
radiometry of a group of images. Then, based on user preferences,
it generates target output values for every input pixel. Pixels
are then shifted based on several user parameters and constraints
from their current Digital Number (DN) value to their target
DN. Overall this has the effect of resolving aforementioned
problems and “evening out” the radiometry of the imagery.
- Project setup: Most photogrammetric packages have an initial
step where the operator defines a coordinate system, adds
images, and provides the photogrammetric system with general
information about the project. Ancillary information may include
data such as flying height, sensor type, the rotation system, and
photo direction.
- Camera Information: The operator needs to provide information
about the type of camera used in the project. Typically the camera
information is stored in an external “camera file” and may be used
many times after it is initially defined. It contains information such
Until recently, the photogrammetric workflow has been relatively static. With the
advent of digital photogrammetry, numerous application tools are now dedicated to
various parts of the workflow.as focal length, principal point offset, fiducial
mark information, and radial lens distortion.Camera file information is typically
gathered from the camera calibration report associated with a specific camera.
- Interior Orientation (IO): The interior orientation
process relates film coordinates
to the image pixel coordinate system of
the scanned image. IO can often be performed
as an automatic process if it was
not performed during the scanning
process.
- Aerial Triangulation (AT): This process
serves to orient images in the project to one another and a ground coordinate system.The goal is to solve the orientation parameters (X, Y, Z, omega, phi, kappa)for each image. True ground coordinates for each measured point will also be established. The AT process can be a time-consuming and critical component of the digital photogrammetry workflow. Sub-components of the AT process
include:
- Measuring ground control points
(typically surveyed points)
- Establishing an initial approximation
of the orientation parameters (rough
orientation)
- Measuring tie points (this is often
an automatic procedure in digital
photogrammetry systems)
- Performing the bundle adjustment
- Refining the solution: removing or
re-measuring inaccurate points until
the solution is within an acceptable
error tolerance
Fig. 1 The ADS40 image of the Miura Peninsula area of Japan was captured by PASCO in 2001
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