Aligning Historic Imagery
Metashape has greatly improved in its ability to align historic Aerial imagery. Here , I outline the steps to get the images aligned properly.
Load Photos
Georeference Photo Location (Optional)
You can georeference photo locations by using the rough location provided by LINZ (Aerial footprints on LINZ Data Service). My preferred method is to overwrite the GPSLongitude and GPSLatitude EXIF tags, but you can also do this manually after the images have been loaded into Metashape. Make sure to set the location accuracy to a reasonable value (I usually opt for 5000m).
You do not need to take this step, you can geo-reference the model later.
Images with referenced location
Load Photos
Load the photos using the GUI:
- Open Metashape.
- Go to
Workflow>Add Photos. - Select and load your images.
Place Fiducials
Identify fiducials on the images and place them. The Tools > Markers > Detect Fiducials tool might be handy if the number of photos is large. This step is crucial to the succesful alignment of the images, so manually adjust fiducials if necessary to ensure accuracy.
- An image with fiducial marks. Note the camera number (20902) is visible below the bullseye in the image, and the focal length (615,70) is legible above it.
Calibrate Camera
In the Tools > Camera Calibration menu, select all images, tick the Film with camera fiducial marks checkbox, and then merge all groups into one camera by selecting all groups, right clicking and choosing Merge Groups. Either auto-calibrate the camera fiducials by right clicking on a photo ( see image) , or get the values from the calibration certificates located at: \\file\Shared\SEESPhotoDatabase\Archive\LINZ_Camera_calibration
You can also obtain the focal length of the camera from the LINZ data.
Note that the y-axis points down
The Camera Calibration Interface
Align Photos
Align the photos as you normally would.
Steps:
- Go to
Workflow>Align Photos. - Adjust settings as needed for your specific project.
- Run the alignment process.
Place Markers
If you need a precise location of your model, you will have to identify points in your image and georeference the model. This ensure greatest accuracy, however you could also do this step in a GIS application. Make sure to reset image location and re-align photos ( I prefer this over optimising cameras).
Generate Outputs
Create the point cloud, DEM, or orthomosaic, export, and bask in the beauty of your historic landscape.