Using conventionally-collected 3D polylines as ground control

My firm is working on a proposal for detailed topographic mapping of three quarters of a mile of roadway for a city DPW. We plan to collect much of the data with our drone and process it in PIX4DMatic and PIX4DSurvey, but the city needs elevations on the curbs, gutters, etc. to an accuracy beyond what the drone can provide because they intend to install ADA ramps.

Since we plan to locate the curbs conventionally, we are wondering if there is a way to bring our conventional 3D polylines representing the curbs into PIX4DSurvey and use them to further “tie down” and improve the overall accuracy of the drone data. In other words, each vertex of the polyline would act like a GCP but rather than define a GCP every 50 feet (for example) along the curb, just define the beginning and end of the curb line with a GCP and have the software interpolate the intermediate shots to create GCPs. The curbs are all straight lines.

I assume this functionality isn’t native to PIX4DSurvey but can anyone think of a workflow that would allow us to do this? Thanks in advance!

Hello mspiegel

In Survey/Matic nowadays is not possible to do it :frowning:

I like this idea, but in order to use the curb vertices as a GCPs they should be clearly visible, and detected in the images to be measured. The initial and last curb points should be easy to locate in the images, but the interpolated points could be are not easy to found.

I’ve used a topographic as a reference to extract GCPs and not all the points are always well defined in the images.

Sorry for not being able to help you much. I’ll give it a look and see if I can think of anything.

All the best,


Hi @rafel.fibla

I appreciate you responding to me! Let me know if you think of anything!



Hello Matthew,

I have not found any way to automate this process. The only way I can think of is to do it manually.

Step 1: From cad to csv:

1- The command DIVIDE in order to the points belong the curbs.
2- The command DATAEXTRACTION to export the points to csv

I haven’t used autocad in a long time. Surely there is a better way to export points to csv or some other software to do it.

Another option would be to make a small routine that reads the dxf, seeks the lines. Using the initial and end points, calculates the interpolated points and exports them to csv.

Step 2: From csv to Pix4Dmatic GCPs:

1- Import GCPs from the csv
2- Mark the GCPs in the images, and discard the points that are not clearly identifiable or use them as Checkpoint

Sorry again, I can’t find the way to automate this process using the current features.

All the best!