One basic and very rough way to assess the alignment quality of your images is to look at the generated cameras' and points' count,
and at values in the Alignment report (see the figure below), as well.
Further, you have the possibility to display matches among your images, which is more accurate, provided that the connections found are correct. You can also display Lens Distortion in the 2D image view context ribbon and verify if the distortion grid is realistically bent. Another, even more apparent and thorough, (and probably the best) way to check the alignment quality is to use the Inspect (I) tool. All of them will be covered in the following lines.
This panel appears after clicking on a component in the 1Ds view:
Statistical values coming from alignment process are stored in the Alignment report. These values also say something about the alignment quality:
Total projections value tells you how many times are 3D points seen in images. For instance, if you have a 3D point visible in 3 pictures, 3 projections will be created. You get the Total projections number by multiplying the Average track length by Points count.
Average track length refers to projections. When you divide total projections by points count, you will get the number you can see in the average track length line. This number indicates in how many images, on average, a point appears. The higher the number, the better interconnected a scene is.
Maximal error (pixels) is the greatest error of a point projection.
Median error (pixels) Median error of all points. The smaller, the better. Ideally under 0.5px. In our example (picture at the top of the page): half of all projections' median error is better than 0.478360 pixels.
Mean error (pixels) Average error. The smaller, the better. Ideally under 0.5px.
Geo-referenced This field says whether a scene is geo-referenced or not.
Metric This one tells you whether a scene uses correct units of measurement.
Alignment time The time lapsed until the alignment completion.
Check dependencies between cameras
Display matching points between images