Pix4d Rapid and Full mode difference and fault

I saw a wonderful thing when I was practicing road capturing by my drone for road 3D simulation without GCP. I test several method for this case . one way path image capturing had not any fault if overlap was enough but go and return in a line near center of road had strange result.

in the video , first we see full mode method of image processing by pix4d pro . the road is like an arc . if we use rapid mode method , the road will be simulated correctly.