Long Roadway Corridor Question

PIX4Dmatic PIX4Dmatic Questions/Troubleshooting
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Not sure if this should go here or under Pix4DMatic category, so I’ll put it here.

Our company is purchasing a DJI Mavic 3E with RTK to photograph a 4.5-mile roadway corridor regularly for progress updates and earthwork volume quantifications. While Pix4DCapture can program this as a single flight, due to line of sight issues, even setting up in the midpoint of the corridor creates issues with VLOS. So I’m thinking that we need to run this as 2 or 3 missions then combine them. I guess the questions are is this the correct way to plan it, and once the missions are run, do we upload all of the photos to Pic4DMatic together as if they were one flight, or do we need to upload as if they were separate missions then merge them in Matic?

Also, slightly off topic, but DroneDeploy stated to me that with M3E RTK we’d only need 1 or 2 GCPs, is that the same with Pix?

TIA.

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You can upload all of the images together. Unless there was something drastic such as fading light or a storm you will be fine.

You will need more than 2 GCPs.

Don’t forget, a properly georeferenced map will also have check points to independently “check” the accuracy of your outputs.

Link to Pix4D GCPs info: Number and distribution of ground control points (GCPs) in corridor mapping

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Thanks for the reply. That article isn’t very helpful with giving an idea of number of GCPs needed. Is DroneDeploy using some special algorithm where they can get away with just a couple of incidental GCPs with an RTK drone that Pix4D doesn’t have? Part of the point of using a drone w RTK is to avoid setting a ton of GCPs, which in a roadway construction project, will need to constantly be reset as the phasing changes and the GCPs are destroyed.

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Hi @scavendish,

Thank you for your message.

Please note that we can’t provide an exact number of GCPs needed.
In case of a corridor project, please check the article suggested by @jaja6009.
In addition, I would suggest to have at least one at the beginning, one at the end, and one in the center of the corridor. However, this might depend on the shape of the project area.
Imagine the area as a large table and the GCPs as the legs that will support it. If all the “legs” are placed at the same location of the “table”, then it will tilt. If the “legs” are homogeneously spread, then the “table” will be stable. Additionally, it is also recommended to place one GCP in the center of the area in order to further increase the quality of the reconstruction.

Here is a generic guideline for placing GCPs:

  • A minimum number of 3 GCPs is required for them to be taken into account in the reconstruction. Each one should be marked in at least 2 images.
  • A minimum number of 5 GCPs is recommended. 5 to 10 GCPs are usually enough, even for large projects. More GCPs do not contribute significantly to increasing accuracy.
  • In cases that the topography of the area is complex, then more GCPs will, indeed, lead to better (more accurate) reconstruction.
  • It is recommended to use at least 5 GCPs, each of which is identified in 5 images, as it minimizes the measurement inaccuracies and helps to detect mistakes that may occur when inserting the GCPs.
  • The GCPs should be placed evenly on the landscape to minimize the error in scale and orientation.
  • Do not place the GCPs exactly at the edges of the area, as they will only be visible in a few images.

Hope this helps

Daniele

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Thanks Daniele, this is helpful. T

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