Number and distribution of ground control points (GCPs) in corridor mapping

Corridor mapping includes project areas that are significantly larger in one dimension than another, e.g. railways, roads, rivers, etc. For more information about capturing a corridor: Step 1. Before Starting a Project > 1. Designing the Image Acquisition Plan > a. Selecting the Image Acquisition Plan Type.

We recommended that corridor projects include ground control points (GCPs) to ensure an accurate reconstruction. The minimum number of GCPs required for a corridor project depends on the same factors as many other types of projects, including the relative accuracy of the image geolocation, the amount of image overlap, and the length and width of the corridor.

We recommend that you allocate your GCPs so that they are offset from one another, regardless of the number of GCPs that you include your project. You can consider including a pair of GCPs at each end of the corridor in addition to the set of offset GCPs that you collected along the length of the corridor.

corridor_mapping_1.png
Figure 1. Recommended distribution of the GCPs in corridor mapping.
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4 comments

  • AP Procurement

    please update or delete this page

    a lot of confirmation has now been made that this is NOT the correct layout for corridor mapping...

    GCPs should be set out in pairs, like ladder rungs as you go along the corridor

  • Teodora (Pix4D)

    Hi,

    Thanks for the feedback. A heterogeneous distribution of GCPs is the general best practice that we recommended and worked for numerous users. If you experimented with more types of GCP arrangements that yielded better results, feel free to share your recommendations with us.

    Cheers,

    Teodora

     

     

  • AP Procurement

    I have first hand experience of induced rolling cumulative errors in pix4D with the layout proposed here.

    If you are going to use a chevron pattern like this, then you really need to close down the spacing to something like 1.5 to 2x your flight height.

    My advice is to lay ground control in pairs, with the pairs positioned at direction changes in the alignment, and not greater than 2.5 to 3x the flight altitude apart.

    Kind of like aeropoints recommend here
    https://www.propelleraero.com/blog/quality-drone-data-part-4-long-corridors/

  • Teodora (Pix4D)

    Hi,

    I am sorry to hear that this GCP distribution did not yield the best results for your projects, there is no "one-size-fits-all" when it comes to georeferencing. The suggestion provided by Propeller Aero is indeed very useful and I will consider it for our future recommendations. I would suggest posting on our community (https://community.pix4d.com/) and sharing your empirical insights to other users who have similar interests. 

    Hope to see you there :)

    Best,

    Teodora

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