Timing for shifting from wgs84 to projected NAD83/UTM with DJI cams

[Jake]

Hi,

We are flying DJI L2 and P1 missions in PPK,
We use emlids, and log a base, PPP it then PPK and retag the DJI pics with the PPP/PPK offsets in Emlid studio.
The PPP is in NAD83, but Geographic coordinates, so the retagged images are in same.  I found I can change the reference on importing in Agisoft from WGS84(4326) to NAD83(4617), and as long as i set the trnsform to none everything lines up.  Then I build as per and export as NAD83/ UTM..  This seems convoluted and when I do the switch to 4617 it drops the camera accuracy to 10m, which I have been resetting to .2m.. I was wondering if I should transform the cameras straight to NAD83/UTM and do all the processing in UTM's or?  We are looking for as close to cm level accuracy as we can get.
The output ortho/dense cloud and ortho products from Agisoft need to be in NAD83(CSRS) UTM's.

Anyone working a similar workflow with advice?


Thanks
Jake 

[BenW22]

Hi Jake,

I fly a using the M300  / P1 combo. I use RTK and reduce simiar (but not exactly) to the method outlined here https://pubs.usgs.gov/publication/ofr20211039 . See pages 3 to 5 for the quick start guide. It is a very good (comprehensive) publication

But yes, the way you import and transform to 4617 is similar to my method. I have carried out many many flights over the years with this combo and consistently obtain very accurate results (<30mm in horizontal) when using GCPs in the MS reductions and additional QA shots as further checks. The GCPs and QA shots are surveyed with Trimble R10 or R12 GPS.

Are you using GCPs and additional QA shots on the ground when capturing your photos? If yes,  I assume you have reduced these to 4617 positions and would then have imported these locations into metashape and transformed your sparse cloud to these locations. This would provide many checks on your final ortho that it is within cms of your GCP and QA checks.

as you probably know - If you dont use GCPs and additional QA shots you dont have any checks on the accuracy of your final data output (ortho etc ).

Hope this has helped.
Kind Regards,
Ben