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Orthomosaic of low voltage class powerline corridor

Hello!

I would like to get some advice on how to approach my ongoing project.

I need to map power line corridor of 10kV lines (poles are 10m high and have three thin wires).
Pictures are collected at 50m AGL (camera synced to lidar, so I have coordinates and all the relevant angles, also used PPK). Frontal overlap 85% and sideoverlap 80%, did a grid flight vica-versa.

After processing, when looking at the output orthomosaic the wires are doubled and do not align at all. Also poles are almost not seen, they seem to be transparent or something.

Any advice would be much appreciated. Thanks in advance.

Forgot to mention that GSD is average of 1.5cm

Hey Madis,

Thank you very much for sharing information about what you want to do and your reaction to your latest results. Please read the entire message before you return to working with your project and don’t hesitate to let us know if you have any questions or if a concept is not intuitive.

After processing, when looking at the output orthomosaic the wires are doubled and do not align at all.

It is possible the wires in the orthomosaic are doubled and do not align with other things in the project area due to inaccuracies in the optimization of the camera’s internal and external parameters. However, considering your initial image positions were measured with PPK, I think it is reasonable to safely assume, for now, the camera’s internal and external parameters are not the first things we should try to troubleshoot.

Instead, I anticipate the wires are doubled and do not align with other things in the project area because the geometry of the wires is not reconstructed in the digital surface model (DSM). I recognize you may already be aware of how Pix4Dmapper generates an orthomosaic, but to make sure you and I have the same understanding; Pix4Dmapper does not stitch images together at the edges.

Instead, Pix4Dmapper projects image content on the surface of the DSM to ensure the orthomosaic is as geometrically accurate as possible. You can see what your DSM looks like either by opening it with the Mosaic Editor in Pix4Dmapper or by opening the DSM GeoTIFF with a third-party GIS or CAD software.

Unfortunately, I believe you will see the geometry of the wires is either missing in some places or does not exist at all. Please let me know if you can clearly see the geometry of the wires in the DSM.

In this case, if the geometry of the wires is not represented in the DSM, Pix4Dmapper projects the image content that represents the wires on the ground. When there is a discrepancy between the image content and the geometry of the project area according to the DSM, a common outcome is you will see the same thing reconstructed in multiple places or not aligning with itself and other things in the orthomosaic.

Pix4Dmapper does not support stitching images together. Therefore, to salvage the project and generate an accurate reconstruction of the wires, you must produce a DSM that accurately represents the geometry of the wires.

Generally speaking, there is more than one way to troubleshoot a project, and this project is no exception. I anticipate the most reasonable method is to increase the density of the dense point cloud while also maintaining a reasonable amount of noise or false-positive points, i.e., points that do not accurately represent the project area, in the dense point cloud.

To increase the density of the dense point cloud, you can manipulate one or more of the processing options and then process the corresponding step or steps. I suggest that you start by considering the processing options for step 2. Point Cloud and Mesh. More information about each of the processing options is available in the support documentation.

I suggest you change one option at a time and then generate a new dense point cloud, instead of changing multiple options at the same time. However, I recognize that it may take a long time to process step 2. Point Cloud and Mesh, so it will be tempting to change more than one option before processing the step.

I understand you may feel that changing one processing option at a time feels tedious. I hope that changining one processing options at a time will help you get a better grasp of how you can influence the way Pix4Dmapper interprets your image content and generates your results.

After you believe the dense point cloud is as dense as possible without containing too much noise, you can generate a new DSM and orthomosaic by processing step 3. DSM, Orthomosaic and Index.

Please note that the original DSM and orthomosaic you generated will be deleted or overwritten if you process either step 2. Point Cloud and Mesh or 3. DSM, Orthomosaic and Index. If you want to maintain a copy of the original DSM and orthomosaic, you can create a copy of the GeoTIFFs and save them in a separate folder before you manipulate your project.

Also poles are almost not seen, they seem to be transparent or something.

I anticipate the poles appear to be transparent, as if they are fading in the ground beneath them, for the same reasons the wires are duplicated and not aligned with other things in the project area. Therefore, I believe you will address the issue you have with the poles at the same time you address the issue you have with the wires.

Please let us know if you have any questions.

Have you looked at Pix4DSurvey? Assuming you are using the ortho to digitize the power lines and poles, it’s much easier to accomplish this using Pix4DSurvey.