Trouble with Control Points

Hi All!

Currently processing a model with 3 GCP's. I have imported the co-ordinates and selected the relevant co-ordinate reference system. When I pick the points in the editor for 2-3 photos, they appear in red. The GCP's successfully import after I pick my points. However, after running AT, the model appears to be floating along the Z axis. Is there something I am missing?

Parents
  • Couple of things .. 2 to 3cm accuracy from drone for this sort of job is optimistic .. the basic rule-of-thumb is Accuracy = 3 x GSD ... so you are shooting sub-cm pixels - for 15km of road .. probably with cheap(er) cameras/lenses .. that is keen.

    Secondly - you can only be as good as your control .. how are you getting the values for the control? RTK GPS? Static GPS for 6 hours+? Total station? If RTK - you have more than 2 to 3cm in the control alone .. 2 to 3cm in X/Y .. up to 4cm in Z.

    Moving on - try running the AT first up on the imagery without the control - this assumes there is at least some level of GPS on the drone(s). You should at least get an AT that resolves ..

    Now add your control to the block .. you should get red circles in the 3D view where the control should be .. are they at least in roughly the right place? If not - check eastings versus northing - numbers in the correct columns? Correct coordinate systems? Hover over the red circle you should get the control mark ID - the one your are expecting?

    If this works .. try nominating 4 control marks in 4 photos each and run it .. this should plonk it roughly in the right place .. makes the hints easier to pick in the imagery.

    Pick more on the next AT etc ..

Reply
  • Couple of things .. 2 to 3cm accuracy from drone for this sort of job is optimistic .. the basic rule-of-thumb is Accuracy = 3 x GSD ... so you are shooting sub-cm pixels - for 15km of road .. probably with cheap(er) cameras/lenses .. that is keen.

    Secondly - you can only be as good as your control .. how are you getting the values for the control? RTK GPS? Static GPS for 6 hours+? Total station? If RTK - you have more than 2 to 3cm in the control alone .. 2 to 3cm in X/Y .. up to 4cm in Z.

    Moving on - try running the AT first up on the imagery without the control - this assumes there is at least some level of GPS on the drone(s). You should at least get an AT that resolves ..

    Now add your control to the block .. you should get red circles in the 3D view where the control should be .. are they at least in roughly the right place? If not - check eastings versus northing - numbers in the correct columns? Correct coordinate systems? Hover over the red circle you should get the control mark ID - the one your are expecting?

    If this works .. try nominating 4 control marks in 4 photos each and run it .. this should plonk it roughly in the right place .. makes the hints easier to pick in the imagery.

    Pick more on the next AT etc ..

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