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DTM generated contours missing a contour.

Perhaps someone can point out where I might be going wrong. I have a project (first project with Pix4D) that I have finally gotten to output contours. The results look great and I am still ‘playing’ around with the settings to determine what resolution, etc. I want to use to the produce contours. I’m noticing that, for some reason, the dxf file with the contours skip a contour. In this case, I have a 2177 and a 2179 contour line, but I do not have a 2178 contour line. When I run the contours with a 0.5’ resolution, still no 2178 contour, but if I run the resolution at 0.25’, I get a 2178 line, but no 2178.25, I do have a 2178.5.

Am I doing something incorrectly? I followed the guidelines on this site and I know that my results compare vary favorably with other contours that I have generated on this project.

Should I just use the 2178 contour from the 0.25 resolution and put it into my 1’ contours and call it good?

Any advise or tips would be appreciated.

Hello Andrew,

Could you please try to export the contour lines as a shapefile (.shp)? Do you observe the same behavior?

In case that there is no missing line in the file format, you could export the shapefile as .dxf from any GIS software. Please let me know if this solves the issue.

Regards,

We have noticed a single missing contour line from the DXF output on two separate projects now. Was there a solution to this issue?

Jeff,

The easiest solution that we came up with was to export as a SHP file and then import the SHP file into, in our case, Carlson Survey, but I’m pretty sure that you can import a SHP file into AutoCAD as well.

You might want to look into the Global Mapper software. It gives you a powerful suite of tools that you can use to clean up point clouds (i.e. remove noise from the point cloud from sources like vegetation or buildings) and then create your resulting surface. I found that Pix4D doesn’t work so well in contouring with flat-pitched roofs (I live in a desert area and most buildings around here have very flat roofs, it confuses the classification scheme) and tends to want to contour up to the roof, and the point cloud editing tools in Pix4D tended to be a bit difficult to use effectively for the purposes of smoothing the point cloud.

Good luck!

Hello Jeff,

Please review your contour lines settings as explained here. Maybe there was something not well defined.

As for the editing tools in Pix4D, please read this article.

Another tool which helps to improve the point clouds and therefore the DSM/DTM is to draw a surface as it is described here.

Regards.

Hi Daniel,

I’m having the same problem with my models.

There is a bug on PIX4D on generating .dxf Contour Lines. There is always one line missing.

Please verify this issue and fix it on the next update.

Regards

 

Hi Marcos,

You are right, I reviewed our documentation and indeed it is a known issue.

We will try to fix it in future releases.

Thank you very much.