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Core
Technical Expertise
Digital Close-Range
Photogrammetry
Sewall now
offers advanced digital close-range photogrammetry (DCRP) services
to clients in municipal government, transportation, pulp and paper,
and the shipbuilding industry. A precision measurement technology,
DCRP combines digital photography with computing power to capture
highly accurate three-dimensional (3D) data on large objects and
facilities. Precise to thousandths of an inch, DCRP enables companies
to align critical machinery, inspect components of large structures,
and record as-built conditions of facilities and historic sites.
The system of measurement is portable; the process is fast and safe;
and the data are comprehensive. Integrated with computer-aided design
(CAD), quality control, and robotics software, DCRP can be used
to inspect, model, and map civic and industrial facilities; to measure
critical features of bridges, roads, and tunnels; and to reverse
engineer machinery in all phases of construction. For each application,
Sewall is prepared to acquire and process precision 3D spatial information
that meets both immediate project and overall life-cycle requirements.
PREPARATION:
REVIEWING THE SITE
In the
DCRP measurement process, Sewall uses a range of camera systems
to measure targets or features of an object or facilities, including
off-the-shelf digital cameras, high-resolution industrial cameras,
and ultra-high resolution image scanning systems. Because individual
project requirements vary, a preliminary review of the site helps
Sewall determine the specific approach and equipment to use for
proper coverage and the most appropriate method of survey control.
An accurate solution may require only a single image, a sequence
of images, or a series of overlapping images from different perspectives.
The camera platform can vary from such extremes as a standing position
on the ground to a helicopter as needed to access the features.
For
more information on Sewall camera systems, see Cardinal
Points.
TARGETING:
ESTABLISHING DIMENSIONAL CONTROL
At the site,
Sewall targets specific control points that will be visible in the
subsequent imagery. When possible, Sewall uses pre-existing survey
data for this purpose. If new data are required to identify coordinates
of additional points, Sewall utilizes a range of equipment, from
traditional surveying tools to geodetic-grade real-time kinematic
(RTK) GPS receivers. These data are critical for orienting and scaling
the images.
IMAGING:
DEVELOPING DIMENSIONAL STABILITY
For each project,
Sewall acquires an appropriate number of images of sufficient quality,
overlap, and symmetry to develop a stable image network for both
measurement and documentation purposes. From this image network,
Sewall is able to measure very precisely the individual attributes
and geometry of the specific object or facilities. The images can
be processed either within the camera system or downloaded to a
workstation on site or at our production facilities.
MEASUREMENT:
DETERMINING OBJECT GEOMETRY
In the measurement
process, Sewall utilizes close-range photogrammetry software to
determine the x, y, and z coordinates of the key features
of the object or facilities. Automated scaling and error-detection
procedures further refine these measurements. To ensure that the
data portray accurate object geometry within project parameters,
Sewall analyzes the measurements on each point for proper triangulation
closure and image quality closure. From these data, Sewall can derive
additional points or hidden attributes of the object geometry, including
planes, surfaces, lines, points, and cylinders, without actually
touching, or manually measuring, these attributes. In addition,
Sewall can review and reprocess the imagery at a later date without
revisiting the site.
APPLICATION:
INTEGRATING TECHNOLOGIES
Sewall integrates
DCRP measurement images and coordinate data with complementary technologies
for a wide range of applications. To meet specific client needs,
Sewall imports measurement data into spreadsheets for reporting
and point cloud distribution. Linked with CAD software, Sewall visually
enhances measurement data for 3D modeling, reverse engineering,
and facilities mapping. Sewall integrates DCRP measurements with
numerical control software to drive robotic applications, such as
high-precision machining in ship construction, or with SPC software
to automate product and process quality control in industrial environments.
LIFE-CYCLE
BENEFITS
With the use
of DCRP, Sewall provides clients with cost-saving benefits that
can extend beyond the requirements of a specific project.
Unlike other
measurement methods, the DCRP process is rapid and unobtrusive,
creating minimal impact on workflow or other surrounding activity.
In harsh or dangerous environments, DCRP makes previously impractical
measurement tasks both possible and safe.
The large number
of images Sewall captures in the process produces highly precise
measurements of project-specific features. At the same time, these
data form a comprehensive visual record of the site and can be reprocessed
later for additional purposes on other projects. In this way, Sewall
uses DCRP to help clients reduce maintenance and overall life-cycle
costs of the specific object or facilities. Integrated with such
other tools as CAD, quality control, and robotics software, Sewall
offers clients 3D measurement capabilities with unlimited functionality.
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