Messages

16

General / Re: Depth scaling introduces huge error to scale bars

« on: October 14, 2022, 04:04:30 AM »

Hi there,

I also use Metashape for this purpose frequently! Like Alexey said, the best way to get around this is to set very low accuracy for the X and Y values and high accuracies for the Z coordinates. Your scale bar accuracies should be pretty high based on your measurements (probably an accuracy of .5mm is reasonable), and for the depth GCPs, your Z accuracy should probably be around 0.1 meters or thereabouts if you're using a dive watch to collect depths. The XY coordinates will be arbitrary (unless you're setting up some kind of specific local coordinate system) so you should set the accuracies of those to a very high value like 100m so that Metashape won't try to take those into account with the same "weight" as the scale and depth. To do this you'll want to type in something like 100/0.1 in the accuracy column for the depth GCPs. The / tells the program that you're setting the XY and Z accuracies separately. Then if you update the transform, you should get good depth and proper scaling at the same time!

17

Bug Reports / Historic Aerial Alignment

« on: November 17, 2021, 07:57:42 PM »

I'm having an interesting issue with the alignment of historic aerial imagery in Metashape 1.7.3. I have a set of 69 scanned photos for which I have the focal length and film size/scan resolution. Most of the scans include all the fiducial marks, but some of them have one of the marks (on the top) cropped just out of frame. They are all sized the same in terms of pixel dimensions, so Metashape automatically recognizes them as a single calibration group. If I do not check the box for film camera with fiducials, Metashape is able to align all the photos without any issue, as there is plenty of overlap to work with. This method introduces some significant errors, however, because while the scans are the same dimensions, they're not all aligned perfectly to the fiducials, and thus the camera calibration is not super accurate. When I try checking the box for film camera with fiducials, and then calibrating fiducials, it does a good job of predicting the location of the fiducials that aren't set manually, even if the 4th one appears out of frame. At that point in the process, it seems like Metashape is doing it's job well. When I try to run a camera alignment after doing all the fiducial work, it cannot successfully align the set. Sometimes I get up to 34 cameras aligned, and the program seems to do a good job with the calibration, but I am unable to get the rest of the set to align. I'm not sure how to proceed because the project requires a high degree of accuracy (~1m or so), so any help would be much welcome. I guess a part of the question is whether Metashape is able to deal with historic imagery where in some cases, one of the fiducials is out of frame. Thanks!

Will

18

Feature Requests / Re: Export report to machine-readable format

« on: August 18, 2021, 04:28:22 PM »

+1

19

Feature Requests / Median Orthomosaic Blending Mode

« on: August 16, 2021, 04:49:16 PM »

In most cases, the currently existing average and mosaic blending modes for orthomosaic generation work well. There are, however, circumstances where using a median blending mode instead of average would be incredibly useful. The example I've come across is creating drone-based orthomosaic maps where the water surface is present - if there's surface reflection / glare, then the mosaic blending mode produces very noisy results, because some images have extreme glare while others do not. The average blending mode solves the reflection problem, but introduces other issues, such as ghosting of objects that have poorly defined geometry, especially defoliated trees / shrubs, and the influence of especially bright spots or lighting changes on some image areas. A third blending mode, which simply uses the median pixel value for a given location, should help to solve some of those issues.  Median blending should be very easy to implement - it's already possible to accomplish in a GIS program by mosaicking exported orthophotos. It would save lots of time and effort to simply include it as an alternative blending mode within Metashape, though! If people have ideas about using Python scripting to accomplish this, that would work too  .

20

Feature Requests / Underwater Photogrammetry: Mask by Depth

« on: July 20, 2020, 06:13:04 PM »

When using Metashape with underwater datasets, dense cloud noise is sometimes generated from source imagery from more distant photos. Water clarity can be a real issue with underwater photogrammetry, and a simple solution to the problem would be enabling a way to generate masks from depth maps. If after setting scale, you could set a distance threshold (say 4 meters), and areas where depth maps indicate that the camera is more than 4m from the surface to be reconstructed would be masked out. It seems like this wouldn't be too hard to implement and would enable significant improvements in underwater model clarity.