No, it is only referring to individual markers.
A marker placed in only one photo simply defines a 'ray' i.e. a line originating at the camera location and extending to infinity on the direction of the position it was placed on the photo.
That same marker placed in a second photo defines another 'ray' and where those rays intersect, is the 'position' of the marker in 3d space.
These rays are also referred to as projections in metashape/photoscan and the same applies to image tie points as well.
Without having two rays/projections defined by the same marker in at least two images, there is no way to infer the 3d position, and so any marker with less than two projections (occurrence in two images) is basically useless.
Furthermore, it is most likely that two rays will actually not intersect at all, due to imprecision in placement and inaccuracy of estimated camera orientations, so the 3d point is actually the point where the rays come closest to intersecting. If you then go on to place that same marker in a third, forth, fifth image and so on, the number of projections increases respectively and so the 3d point is where these multiple projections come closest to all intersecting. If the markers are placed precisely, then this greater number of projections/rays should help to increase the accuracy of the marker.
If the cameras were not well aligned then after adding a marker to multiple images in this way hitting the optimise button should adjust alignment to bring the projections to a closer intersection.
All this only applies to a single marker, placed in multiple photos. I.e. "point 1" in photos "DSC_0001.JPG", "DSC_0002.JPG" and "DSC_0003.JPG" means that "point 1" has 3 projections.
It will generally be necessary to use multiple markers in a project but how many you need, and how many you need in each photo will depend on what you are trying to achieve and what kind of photo set you are working with.
Topic: Placing markers (Read 7105 times)
