Post

2 followers Follow
0
Avatar

Issues with scale in recent MME processing

I am in the field and processed a new map with three flights and the resulting ortho did not match up with the existing aerial imagery background.  I think I accidentally loaded the three ground photos to the uploads.  Would that cause the scaling to be off?  I would like to try the process again but wanted to see if i can get a refund of those points.  Thanks,

Timothy King

Official comment

Avatar

That is certainly an odd issue. Having more than one ground reference image wouldn't do that. 

The issue here is likely the data collection: there is too much of it. You used 80/75 overlap in a full grid. This corresponds to 40+ looks at everything in the scene but certain parts of it were taken at significantly different times which changes their appears due to shadow motion. The data collection started at 8:29 am and ended at 9:04 am. This means that the images in certain place had images taken with wildly different lighting (shadows move the fastest early and late in the day). This can cause all sorts of issues since it affects the system's ability to calculate a camera calibration. There are no tall leafy trees in the survey area so using that much overlap was total overkill.

The good news: You had way too much overlap so you can just upload half your data and it will likely be fine. It is always better to take too much as opposed to too little. 

The only time we ever actually recommend using the full grid layout is when you are covering a small area like a building to try to get all the angles and overhangs. It is usually accompanied with tipping the gimbal up a bit. When used over a large (20-ish acre) area like this it puts too much time between the photos. 

Since your data was collected using Map Pilot and this isn't specifically covered in the Data Collection guidelines (it is mentioned in the 3D capture article and the Data Collection guidelines mention avoiding motion and lighting changes) we will grant a one-time 50% refund which should be exactly what you need to process half the data. Images DJI_0011.JPG through DJI_0333.JPG would be a good start.

Side Note:

Technically you could fix it with the manual rereferencing tool. If you created a GCP file with coordinates of some real world landmarks from the basemap and then dragged the markers to the corresponding features in your map it would stretch it back out. 

Zane
Comment actions Permalink

Please sign in to leave a comment.

1 comment