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Issue with DTM & Contour using Pix4D in a Quarry Area

Good Morning!

We were trying to process the Anafi Drone Data using Pix4D Software for a Quarry Area.

The Drone Mission contains 566 Images which were processed to get the Ortho Images, DTM, DSM & Contours.

After studying the data we have observed that the DTM / Contours generated by Pix4D have issues with the elevation information.

Figure-1 shows the Elevation in a cliffed zone where it should not be.


Figure-2 shows the Elevation Difference of 7 Meters along a ROAD (12 Meter width) which is practically impossible.

It would be great if someone can advise me where the error peeped in.

Thank you in advance and have a great day!

Regards,

1 Like

Hi Naresh,

Could you please attach your quality report (and log) to your reply using this:
image ?

Have you been using GCPs?

Looking forward to have a look on your QR.
Best

Anafi_Hafirah_Part2_report.pdf (556.4 KB)

Dear Marco,

Good Morning!
Thank you for your reply and please find attached the requested log file and the report file.

14 GCP’s have been used for this project.

Can you please throw some light on how the DEM is generated and from where the Elevation is taken (Is it from the Sensor / GPS of the Drone / the pre-defined Elevation Model in Pix4D) in generating the DEM.

Thank you and have a great day!

Regards,

Uploading: Anafi_Hafirah_Part.txt…

Kindly rename it to .zip as the file is too huge to be uploaded.

Hi Naresh,

The DSM and DTM are spatially interpolated using either the Inverse Distance Weighting or the Triangulation algorithm. Rather than assume one interpolation method is better than another, you should try both interpolation methods on your dataset and compare the results to determine the best interpolation method for your project.

After doing this, please make sure that the contour lines were generated from the right 3D model (DSM or DTM). If you intend to obtain also the DTM, please note that Pix4Dmapper generates the contour lines based on the DTM.

I would cross-check the contour lines generated in Pix4Dmapper by also extracting the contour lines using the free software QGIS (download link here) and following these steps:

  1. Open QGIS and create New Project.
  2. Open the DSM with the key combination Ctrl + Shift + R. This is how it should look like (top left is the New Project button):
    image
  3. Use the key combination Ctrl + Alt + T to enable the Processing Toolbox (as seen in the screenshot below), then type contour :slight_smile:
    image
  4. Select the tool from GDAL Raster extraction called Contour, set the desired options (Interval between contour lines =elevation interval in Pix4D, Offset from zero relative to which to interpret intervals =contour base in Pix4D), choose a folder where to save the contour lines and select the output format:
    image
  5. Click on Run .
  6. The results should be displayed in QGIS:
    image

Cheers,
Teodora

Good Morning Teodora,

Thank you for your email.

We could not achieve the expected results using both the options (Inverse Distance Weighting or the
Triangulation algorithm)

Anyways, thank you for your time and have a great day!

Regards,

Naresh Puripanda |****- Specialist IV - GIS | Office: +973 1714 8937 |www.tatweerpetroleum.com

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