smoother contour lines

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

is there a way to smooth out the contour lines a client was concerned about jagged lines compared to a traditional survey done with smooth contours.

will adjusting surface smoothing in step 3 effect contours generated from the DTM ?

2

Hello Ramiro,

Since the contour lines are based on the DSM and the DTM is based on the DSM. So the contour lines generated by the DTM, will also depend on the DSM. 

What you could do is to modify is the Processing options of the Contour Lines to make them smoother. 
To do so, 

  1. On the Menu bar > Process > Processing Options
  2. Click 3. DSM, Orthomosaic and Index and select the tab Additional Outputs
  3. In the section Contour Lines change the Resolution.
  4. Click OK.
  5. On the Menu bar > Process > Generate Contour Lines…

Make sure you have processed Step 3 and the DTM is generated so that the contour lines will be based on the DTM. 

The Resolution defines the horizontal distance for which an altitude value is registered. 
You can adjust this value and the higher it is the smoother the contour lines will be. 

You will find all the analytical information here:
https://support.pix4d.com/hc/en-us/articles/202558419#label2

 

Best Regards, 

3

I have the converse problem

I have run a DTM generation, with a resolution of 5 x GSD (recommended values) - but the surface that comes from this is very rounded / soft - to such an extent that surfaces I am certain are horizontal, such as roads, have a significant rounding into a slope.

Are there any recommended parameters to control this? - it seems a little of a black box solution

I have read the paper on the Pix4D algorithm, I just don’t see much granularity of control for this in the settings

 

My alternative method is to use cloudcompare from the original and progressively use the CSF filter assuming steep processed slopes and resolution at varying values to remove vegetation / upstanding materials

I then re-raster this surface at a modest resolution to produce a lowest point per 0.5m grid say.

A bit time consuming

4

Hi,

 

Unfortunately, there are no parameters that would control the smoothness algorithms. To better understand your case could you post here the quality report and a screenshot of the DSM vs. DTM?

 

Thank you,

Ina

5

The recommendation in step 3 “change the resolution” has not recommendation on typical settings to try using based on common interval settings. The software defaults to 10 m with a resolution of 100 cm, this default seems appropriate for environments with large elevation changes. In many cases the contour elevation intervals are closer to 1 m (3 feet) and even leaving the resolution at 100 cm, the contours still do not approach the smoothness of a traditional contour map produced by a Land Surveyor. Although I would point out this is going to be more accurate that most traditional methods other than a terrestrial Lidar scan.

Would you not agree that if your intervals are 1 m that the resolution should not be increased to larger than the default 100 cm for something like a 50 hectare area with no more than 25 m of elevation change?

I think this is an area Pix4D can improve on both in the documentation (add some recommendations for some common scenarios and in the software settings themselves.)