Prepared by Richard Hassler, Joe Blecha, Troy Brown, Ed Ryan
Trimble Business Center (TBC) calculates scale factors to correctly align different types of raw survey, scan, and point data in one project
New tools for collecting survey and scan data offer opportunities for completing large projects over challenging terrain more accurately and efficiently than ever before. However, there is added complexity involved when integrating data collected by multiple devices over large geographic areas, due to the curvature of the earth and projection distortions in commonly used coordinate systems.
For many years, scanning professionals have used software packages to process their projects using simple X,Y,Z coordinate systems in a CAD-like environment. The data are left mathematically "untouched" to produce virtual measurements and views that essentially match on-the-ground measurements of the scanned objects at the site. This approach is perfectly sound and yields great results as long as the project does not span vast areas or contain large differences in elevation. For many applications this is the best way to work with the data.
Today, scanning professionals are often asked to marry their scan data to observations from other sensors or to deliver their results in a predefined coordinate system from a government agency. A problem arises with aligning data from a terrestrial laser scanner because multiple scans are registered to each other for relative accuracy, but not georeferenced to a point on the ground. Meanwhile aerial imaging, mobile mapping, real-time kinematic (RTK) and total station data produce survey measurements tied to GPS/GNSS coordinates. To integrate scanned ground measurements with those from other devices that utilize GPS/GNSS coordinates and cover large areas, geodetic computations to scale the scan data are necessary to address positioning discrepancies.
Trimble Business Center (TBC) supports the combining of data from many sources by correctly applying the needed transformations and projections to obtain properly fitting and geodetically correct results. Together the grid and elevation scale factors define a combined scale factor, which is applied where appropriate to allow the scan data to agree with survey measurements or point cloud data from geodetically correct sources.
In TBC, scan data from smaller jobs can be processed using localized projections, resulting in nearly identical results to processing using a simpler X,Y,Z system. But the fact that a proper geodetic framework is utilized ensures that the computations are correct, and the final results allow for proper matching between data from many different sources. TBC automates the calculations to properly position, display, and model multi-source data types in a single-project environment.
For an in-depth explanation of how to use TBC to calculate scale factors, please refer to "Understanding and Applying Scale Factors in Scanning Workflows in Trimble Business Center". This white paper contains information not found anywhere else and is an excellent guide for customers, distributors, and Trimble staff.
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À propos de l’auteur
Trimble Geospatial propose des solutions matérielles et logicielles à la pointe de la technologie pour les professionnels du levé terrestre, du SIG, du scanning, du mobile mapping, de la télédétection, de la photogrammétrie et de l'expertise.