I need a Field Calculator script to select a feature (trees layer), if values from multiple fields, namely the amount of pine, spruce and birch, meet a specific condition: The values of pine "V101__m_3_", spruce "V201__m_3_" and birch "V302__m_3_" columns have to be at least 20% of the total wood volume column "Vtot__m_3_". The "Vxxx__x__x" is the name of the fields.

The values are integers.

How is this done?

I've tried this, but it doesn't work:

"V101__m_3_"+ "V201__m_3_"+ "V301__m_3_"+ "V302__m_3_" > 20/ "Vtot__m_3_"
  • 2
    Could you please edit your question, and add a sample of your data?
    – Berend
    Oct 19, 2021 at 10:42
  • 1
    It's hard to answer without seeing the actual data, but I notice that you are summing 4 values, rather that 3 (pine, spruce and birch). 20% (i.e. one fifth) of the total value would be "Vtot__m_3_" / 5 instead of 20 / "Vtot__m_3_"
    – Berend
    Oct 19, 2021 at 11:00

2 Answers 2


Assuming that you want the sum of the four columns to be greater than 20% (or 1/5) of the fifth, you could also say that 5 times the sum of the 4 columns should be greater than the fifth. The expression would be:

("V101__m_3_"+ "V201__m_3_"+ "V301__m_3_"+ "V302__m_3_") * 5 > "Vtot__m_3_"

It's actually very hard to answer the question by speculating how your data tree looks like. But I assume that you have three fields for pine, spruce, and birch; each has int values as a percentage.

So you could use:

("field_1" / "field_total" *100) >= 20 and ("field_2" / "field_total" *100) >= 20 and ("field_3" / "field_total" *100) >= 20

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