Emerging in recent years, fourth generation SfM is essentially digital photogrammetry, using highly overlapping digital imagery from consumer grade, non-metric cameras. With SfM, highly redundant image overlap allows for self-calibration of non-metric cameras and accurate mapping of point features visible in overlapping images. Has anyone had any experiences using UAVs and this fourth generation of photogrammetry? Or is their a preference for third generation digital photogrammetry introduced in 1991 by the U.S. army engineer topographic laboratories (ETL) that developed the Terrain Information Extraction System (TIES). Is one better for smaller areas of interest compared to the other??ÿ
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Thank you for starting this thread!!
I'm interested in hearing more about where and by whom the SfM generations have been defined. I have studied this subject and have used both types of processing with drone acquired images, but have never seen any references to SfM having been characterized as generational.
What I can share with you is that traditional aerial-triangulation bundle adjustment used in photogrammetry is the appropriate approach for survey-engineering purposes where elevation determinations are critical. Pix4D and Agisoft's Metashape fill that need. There may be other such suitable softwares available, but those are the two that I've used, and I do not know of any others.
SfM techniques are appropriate when non-critical terrain visualizations are acceptable. SfM processing, even when using different mitigation efforts including project-wide GCPs and camera modeling, still tend to distort the terrain. This is sometimes referred to as the bowl effect. There are several softwares available for SfM processing including Global Mapper Pro and Reality Capture, to name just the two I use.
There are also online processing services which I've not extensively tested; however, if you start looking at them, keep in mind the differences between SfM and the traditional aerial-triangulation bundle adjustment used in photogrammetry.
Kind regards,
Kelly
