ACCURACYComing soon
Stream Capture's quality report separates the fit at the points used from the error at points it never saw, states an accuracy class from those independent check points only, and flags what it could not verify.
Stream Capture is in development and not released yet. At launch it will come in the same download as its sister program Stream Terrain; today's download contains Stream Terrain.
The honest measure is the error at check points: surveyed points that were kept out of the adjustment and compared with the finished model afterwards. A model that fits the control points it was forced through says little; the error at independent points says what a user can expect elsewhere.
Reprojection error, in pixels, measures how well the photos agree with each other. It is a sign of a healthy alignment, not an accuracy in metres. Accuracy standards such as the ASPRS Positional Accuracy Standards for Digital Geospatial Data express accuracy as RMSE at check points, and ask for at least 30 of them.
GCP RMS is the internal fit at the points used in the adjustment. Check RMS is the error at independent check points — the real accuracy evidence. The report shows both and never presents one as the other.
The report states a horizontal and a vertical RMSE class under the ASPRS Positional Accuracy Standards, 2nd edition (2023). For Turkish projects it also states the map scale implied by the large-scale mapping regulation, BÖHHBÜY Article 91.
With fewer than 30 check points the report still states the class but adds a warning that it was tested with only that many points and is insufficient.
Reprojection RMS is reported at full image resolution, not at the reduced scale the engine may have worked at, together with tie-point count, ground sampling distance, overlap and elevation range.
DSM and DTM height minus surveyed height is measured at the control and check points and written to the report.
The self-calibrated focal length, principal point and distortion terms are listed with their uncertainty. When the lens data written by the drone is reliable, a self-calibrated focal length that strays more than 2% from it is not adopted.
Written products are read back and checked for outlier heights, no-data mismatches, a DTM above its DSM and stale product files; findings go to the log and the report.
Open PDF Report produces the document you hand to the client, with your company name and logo, in the interface language. Six languages are supported.
It depends on the camera, the ground sampling distance, the overlap, the positioning method and the control. Height is normally weaker than horizontal position. Rather than quoting a rule of thumb, Stream Capture measures your project at independent check points and prints the result.
GCP RMS measures how well the model fits the points that were used to build it, so it is optimistic by construction. Check RMS measures the error at points that were never used, which is the number to quote.
No. Reprojection error in pixels says the photos agree with one another. It does not tell you whether the model is in the right place on the ground. Only check points can.
The ASPRS standard asks for at least 30 for an accuracy class statement. Fewer still give a useful estimate, and the report warns that the class was tested with only that many points.
ASPRS Positional Accuracy Standards for Digital Geospatial Data, 2nd edition (2023), for horizontal and vertical RMSE class. Turkish projects also get the scale class under BÖHHBÜY Article 91.
Stream Capture is in development and not released yet. At launch it will come in the same download as its sister program Stream Terrain; today's download contains Stream Terrain.
About Stream Capture