Incorrect orthophoto geographical location (UK)

[David Quick]

Hi Andrea
I am using the Educational version of 3D Zephyr Aerial to create 3D models of our archaeological trenches in the UK. The source images are obtained from a DJI Inspire 1 drone. I am then trying to add the orthophoto created by Zephyr in our geographical information software (QGIS). In QGIS I use the CRS for British National Grid (27700) and when creating the model in 3DFlow Zephyr I instruct it to use 'British National Grid' as well.

Unfortunately when I import the orthophoto in QGIS the position of the orthophoto is incorrect; it is showing about 60 metres north and about 90 metres west of where it should be. I cannot understand why. I attach a screenshot from QGIS showing the surveyed position (yellow outline) and orthophoto position of our Trench 'U'. (The grid squares are 30 x 30 metres)

May I check please that the 'British National Grid' CRS I am using in Zephyr is EPSG 27700? Can you think of any other reason for the incorrect placement?

Kind regards
David

[Andrea Alessi]

Hi David,

in the next version (and well, in the current beta ) you can select the projection by their EPSG code.

The british national grid pcs seems slighlty different from EPSG27700 - can you try importing in Zephyr the following ProjCS and see if it helps? If not, can you sahre a subsample so we can do some testing?

Thank you!

Copy paste the below data ( taken from https://epsg.io/27700 )

PROJCS["OSGB 1936 / British National Grid", GEOGCS["OSGB 1936", DATUM["OSGB_1936", SPHEROID["Airy 1830",6377563.396,299.3249646, AUTHORITY["EPSG","7001"]], TOWGS84[446.448,-125.157,542.06,0.15,0.247,0.842,-20.489], AUTHORITY["EPSG","6277"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.0174532925199433, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4277"]], PROJECTION["Transverse_Mercator"], PARAMETER["latitude_of_origin",49], PARAMETER["central_meridian",-2], PARAMETER["scale_factor",0.9996012717], PARAMETER["false_easting",400000], PARAMETER["false_northing",-100000], UNIT["metre",1, AUTHORITY["EPSG","9001"]], AXIS["Easting",EAST], AXIS["Northing",NORTH], AUTHORITY["EPSG","27700"]]

[David Quick]

Hi Andrea
I used the data you provided for the CRS and unfortunately the TIF orthophoto is still showing in the wrong position in QGIS. However, the KML file I created at the same time appears to show in the correct position in Google Earth Pro. I have checked the location of the source photos using the MAP tab in Lightroom Classic and they are definitely in the right place.

My source photos are in my Dropbox at this link if you have time to do some testing please.
Thanks
David

[Roberto]

Hi David,

I've made a test with the current beta, using the CRS provided from Andrea (which is now already included by default). The orthophoto exported in QGis seems fine, and it's in the same location of the KML file. I've loaded your orthophoto, and it also looks fine. The KML file has lat-long coordinates, so there shouldn't be any coordinate system problems (left QGis, right google earth):




Maybe it's an importing issue in QGis? I drag-and-dropped the file without changing anything.

[David Quick]

Thanks very much Roberto.
I have come to the same conclusion - that the problem is with QGIS and not with 3DFlow Zephyr. I am grateful for all your help - please take no further action.

Kind regards
David