Soil and plant masking w/ Pix4Dfields

Agriculture Workflow and Application
21

Hi,
How to use the grid zonation map of QGIS in the video convert to a shape file with data (amount, area_ha, avg Value, rate_ha)as like Pix4dfields prescription map?

22

Hi, could you please re-phrase your question as I cannot understand it.

Best,
José

23

How to write the vra data (amount, area_ha, avg Value, rate_ha) into the zonation and convert it into a shape file by QGIS?

24

Hi,

Please open the attribute table of the layer in QGIS, or press “F6”, fill all the fields needed, afterward “save as” shapefile. You can search each step in youtube.

If you have a valid license of our software, please submit a support ticket in order to help you better,

Best.

25

Hi,
When I mask out the soil and grass using a vegetation index within the parameters of a boundary, it appears you can export those statistics to csv.
In the statistics it’s shows total area and then area visible. With these two numbers you can determine a percentage of plant cover or masked area.

Has this been a new addition to the software? As I have asked about this possibility before but was told it needed to go into QGIS to determine canopy percentages.

26

Hi,

You can always export statistics, not only when you masked a layer, you will see under Area visible the area that is covered by pixels inside the histogram (mix/max sliders). So it is strictly related to how you move the histogram
https://support.pix4d.com/hc/en-us/articles/4409231699345-Exporting-statistics-PIX4Dfields

This has been in PIX4Dfields for a while now…
Masking the layers is useful when you need to actually use only pixels with vegetation for analysis zonations etc.

Hope this clarifies your doubts.

Best,

27

Tree assessment and counting!!

Have a look at Tree asessment and counting in PIX4Dfields! 🌳

28

Hi,
How to mask the soil when it is covered with green grass and has about the same index value as the trees? Is it possible then to mask the soil based on height? For example to mask everything below 30 cm.

29

In PIX4Dfields such a function does not currently exist, but its a great idea! However this can be done with free QGIS:

To mask the vegetation index layer using the height information from the DSM (Digital Surface Model) in QGIS, you can follow these steps:

  1. Load the DSM and Vegetation Index Layers: Make sure both your DSM and the vegetation index layers are loaded into QGIS.

  2. Raster Calculator for Height Threshold: You’ll need to use the Raster Calculator to create a mask based on the height threshold from the DSM.

    • Open the Raster Calculator (Raster → Raster Calculator).
    • In the raster calculator, you will create an expression to identify areas where the DSM is greater than or equal to 30 centimeters. For example, if your DSM layer is named ‘DSM’, the expression might look like this: "DSM@1" >= 30. This expression will create a binary mask where values of 1 represent areas where the height is 30m or greater, and 0 where it’s less.
    • Run the calculation and you’ll get a new raster layer with the mask.

  3. Apply the Mask to the Vegetation Index Layer: Now, you can use this mask to filter the vegetation index layer.

    • Again, open the Raster Calculator.
    • This time, create an expression to apply the mask. If your vegetation index layer is named ‘VegetationIndex’, the expression will be something like: ("VegetationIndex@1" * "Mask@1"). Replace “Mask” with the name of the mask layer you generated in the previous step. This expression multiplies the vegetation index by the mask, effectively setting the vegetation index to 0 where the height is below 30 meters.

  4. Execute and Save the Result: Run the calculation. The output will be a new vegetation index layer, filtered based on the DSM height.

Remember, these steps assume that your DSM and vegetation index layers are properly aligned and have the same spatial resolution. If they don’t, you may need to do some preprocessing (like resampling or reprojecting) to make sure they align correctly.

1 Like
30

Hi Julius,

Thank you for your explanation. I discussed your method with my kollege Yves.
we think this method works when the field is flat. But when the fields goes upwards/downwards, then first you have to do DSM minus DTM to obtain a new layer with the absolute height
On this new layer you can do step 2 and 3. What is your opinion about this?
I think processing a dtm is not possible in fields?

greetings
Renaat

31

Hi Renaat,

you are absoulty right! But also that DTM can be cerated with QGIS. You have to sample your DSM (Point Layer, Extract DSM Height by Location) at the points where there is only soil/terrain and from those samples you can generate a TIN Interpolation for example to create your DTM.