Home Articles Photogrammetric Workflows: Traditional, Digital and the future

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