Metashape supports processing of analog aerial images scanned to digital files. On uploading, all the scanned images from the same analog camera should be placed in a designated calibration group. Metashape will automatically put the images to the same calibration group, providing that they have been scanned with same resolution. 


In case scanned analog images from different cameras have been uploaded to the same chunk, it is required to divide them manually into different calibration groups. It could be done in Camera Calibration dialog available from Tools menu. 


Camera calibration (for data sets of scanned images) is performed basing on the fiducial marks information. That is why camera calibration starts with fiducial marks detection in this workflow.


The first step is to load scanned photos

1. Add scanned photos to the project using Add Folder... command from the Workflow menu (Workflow > Add Folder...). 


2. In the Add Folder dialog box browse to the parent folder containing subfolders with images. Then click Select Folder button. 


3. Click OK button to close the dialog. Display of images in Metashape window.




Fiducial marks detection can be only performed for film cameras. Don't forget to enable the Film camera with fiducial marks option in the Camera Calibration dialog box for all the groups which contain corresponding scanned images. 


1. Select Camera Calibration... command from the Tools menu (Tools > Camera Calibration...).


2. In the Camera Calibration dialog box check Film camera with fiducial marks option.



3. Click OK button.


Starting Metashape 2.0, you can specify the Transformation type for scanned images. You need to open Fiducials tab and choose Conformal, Affine or Projective transformation type in the Camera calibration dialog window:



By default Metashape uses Conformal transformation type. Conformal transformation is a linear fractional transformation (please note that is not an affine transformation). Thus the generation of a special conformal transformation involves use of multiplicative inversion, which is the generator of linear fractional transformations. 


Affine transformation is a geometric transformation that preserves lines and parallelism, but not necessarily Euclidean distances and angles. Projective transformation is the composition of a pair of perspective projections. Projective transformations do not preserve sizes or angles but do preserve incidence and cross-ratio: two properties which are important in projective geometry.

Automatic detection fiducial marks

Metashape enables automatic detection of the majority of the fiducial marks types. See the illustration below:



In case your fiducial marks type is not among those supported for automatic detection, please place a feature request with Agisoft support team: support@agisoft.com. 


Run Detect Fiducials... command from the Markers submenu from the Tools menu. You need to specify Detection type of markers (Generic, Right angle, 45 degrees cut, Frame) in the Detect Fiducials dialog window: 



  • Generic: if the fiducial marks in your images are like the examples below (circle with dot, dot, crosshair, and so on), then you need to use Generic type: 


  • Right angle: if fiducial marks represent angles, then you need to select Detection type - Right angle:


  • 45 degrees cut: сhoose this type for fiducial with a cut and with a clearly visible circle above the cut.


  • Frame: use this type as a workaround. In this case the boundaries of the scanned images frame (corners or midpoints of the sides) will be detected.


Also for the Right angle type of fiducial marks you need to specify Fiducials position (Corners and sides, Corners, Sides), according to where fiducial marks are located on the images:



In the Camera Calibration dialog print in coordinates of the automatically detected fiducial marks on the image according to the analog camera certificate. They should be measured in coordinate system associated with the sensor: origin - in the center of the sensor; axes X - to the right, axes Y - downwards; in millimeters (mm).


In the current version of the software camera calibration for the scanned images with fiducial marks that are not supported can be performed manually following the procedure outlined below. 


To calibrate scanned images with non-standard fiducial marks manually

First of all it is necessary to set Fiducials properties in Camera calibration dialog for each camera used for data capturing.


1. Select Camera Calibration... command from the Tools menu (Tools > Camera Calibration...). 


2. In the Camera Calibration dialog box check Film camera with fiducial marks option. 


3. On the Fiducials tab add fiducial mark instances, the number of such instances should be equal to the number of fiducial marks used on the original photos.




4. Print in coordinates of the fiducial marks on the image according to the analog camera certificate. 



They should be measured in coordinate system associated with the sensor: origin - in the center of the sensor; axes X - to the right, axes Y - downwards; in millimeters (mm). 


If there is no camera certificate with fiducial marks coordinates information for the data set in question, then it is necessary to Calibrate Fiducials. For the purpose in the Camera Calibration dialog box run Calibrate Fiducials... command from the context menu of the selected images. All the images from the respective calibration group should be selected.



Specify scanning resolution (mm/pix) in the dialog window so that the program can calculate the position of fiducial marks on the images.


5. Close Camera Calibration dialog with OK button. 


Place all the fiducials on each photo

Then it is necessary to place all the fiducials on each photo from the calibration group. This process includes the following steps:


1. Open a photo in Photo view (double click on the image in the Workspace pane or Photo pane).

). 


2. Zoom in to a fiducial mark center. 


3. Right button click on the targeted fiducial mark and use Place Fiducial command from the context menu. You will need to choose a corresponding fiducial mark instance from the dropdown list. 



4. In case you need to replace one fiducial mark with another right-click fiducial mark and use Replace Fiducial command from its context menu. You will need to choose a corresponding fiducial mark instance from the dropdown list. 


5. After placing all the fiducial mark instances, you can proceed to general Metashape processing workflow. The software will automatically scale and orientate all the photos according to the fiducial marks information.


It is recommended to mask out all the margins with auxiliary information on scanned photos to avoid negative effect on the stability of the processing results:



Use Place Fiducial tool

Metashape supports an intelligent placement of fiducial marks on the images starting Metashape 2.0.


1. Enable Place Fiducial button on the Toolbar:




2. Placing fiducial marks on the images. An intelligent placement of markers will be used:



Place all 4 fiducials:



3. After all 4 fiducials are placed Metashape will switch the image to the next one automatically to continue measurement of fiducial marks on the next image.