DSM Models and understanding the output!

PIX4Dmapper
1

Hello!
I am trying to do a 3D model with vegetation over a 50x50m grid over a specific point. I wasn’t able to collect a GCP so I am depending on only the camera/phantom altitude and geolocation data available. I have been noticing as I am processing the data that there is an overall shade gradient that I don’t necessarily think is an accurate depiction and leading to perhaps some inaccuracies in the data. Is there a way to get a better understanding of the vegetation heights/topography of the landscape without GCPs?

I have attached a couple images from a specific project. You can see the ridges of vegetation and water dispersed in the landscape but those instances aren’t necessarily depicted in the imagery/DSM because there is an overall gradient in the imagery and I have this is every single project!

Thank you so much for your help in advance!

dunlrh04 ortho and dsm
dunlrh04 ortho and dsm1708×771 454 KB

2

dunlno02 ortho and dsm
dunlno02 ortho and dsm1864×850 204 KB

3

Hi Callie,
I’m trying to understand where exactly you are seeing some discrepancies? Are you making reference to the color gradient of the DSM? Do you believe that you do not have the elevation changes in your project area?

As for improving your results without the use of GCPs, I would suggest using a scale constraint. If you have a known distance in your project area you can set that as a constraint so that it helps keep your project to scale and limits any distortions. Scale constraints can be set for the X,Y, and Z axis. You may have difficulty in the Z axis since your area is quite flat and homogenous. But take a look at the article below.

4

Fair enough! I was just trying to see if there was a way to see the vegetation elevation differences more clear rather than the shift in elevation over the whole landscape, can I isolate the vegetation features? Just curious if this was possible through pix4dmapper!
I will definitely take a look at the article you posted below though. Thank you!

5

What you can do is edit the point cloud and assign the points as vegetation. Depending on your project size and the vegetation types this might work.

6

hey michael! is there a way that I can draw a 50x50m processing area around a point on the map? In the imagery, I have a meter stick pointing towards a nest and I am trying to make a 50x50m plot around that point. I am hoping that creating a fully photographed plot around the point will remove any edge effect from the imagery and create a crisp image outline for the orthomosaic and dsm. I havent been able to find a solid way of doing this other than manually drawing a box? is there a different software where I can do this to edit the point cloud and mesh? I would like to be able to do this in pix4d if possible!

Thanks!

7

Hi Callie,
I would suggest using a processing area in PIX4Dmapper. You can import either a shapefile or KML file. Simply draw your area using ArcGIS, QGIS, or even Google Earth then import it into PIX4Dmapper.