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Author Topic: Collect Ground Control from Existing Georeferenced Imagery  (Read 2570 times)

StevenF

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Collect Ground Control from Existing Georeferenced Imagery
« on: September 21, 2014, 12:24:09 AM »
Collecting ground control points from georeferenced images of known accuracy directly within Photoscan could greatly reduce the time and difficulty of collecting ground control for images.

It's often the case that people don't have the time or resources (i.e. expensive gps) to collect good ground control but may have access to existing ortho photos or lidar intensity images of high accuracy that would be sufficient for ground control. Control points can be collected from this imagery in existing GIS software and then imported into photoscan. But why not incorporate this functionality directly in Photoscan?

It would provide two primary advantages to a GIS+Photoscan workflow.

1. Simplification of adjustments to control point location: If ground control points are collected in a GIS program and then imported into Photoscan they need to be re-imported every time you want to adjust the location of the control point on the control image. If collection of ground control from existing imagery was implemented in Photoscan it would greatly increase the speed and ease of this process.

2. Automated control point collection: Feature point detection should already be incorporated into Photoscan as part of the SFM process. Why not use the existing algorithm to auto detect potential ground control point locations in the control/reference image and the images you want to georeference? It's baffling to me that all photogrammetry programs have auto-tie point generation but none have auto-control point generation. Photoscan could possibly be the first to implement this feature which would speed up the ground control collection process immensely.

Photoscan is amazing at simplifying the photogrammetric process with its self-calibrating bundle adjustment procedure, but collecting control points is STILL the most time consuming and difficult part of the photogrammetric workflow. I think Photoscan has the potential to make this part of the process significantly easier which would make it a very attractive alternative to other photogrammetry programs.