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Nautical vector chart

I have information in a point layer with one Z-value per point. It is displayed in the screenshot as a label. I have made an polygon layer with a "min Z value" per polygon. The polygons are displayed in the screenshot in brown, green and orange(ish). I have stored the "min Z value in the database of the polygonlayer.

I want to check if there are Z-values in the pointlayer that are less than specified in the "min Z value" column of the polygon layer.

Example: the "min Z value" for the orange(ish) polygon is 7.00; I want to check if there are any values in the pointlayer within the perimeters of the orange polygon that are less then 7.00.

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Transfer Elevation values to attribute using expression z($geometry) for point and polygon layer(shown in screenshot below).

Attribute Table

Install MMQGIS plugin in Qgis, Go to MMQGIS -> Combine -> Spatial join. In this case Z is polygon Z1 is point.

MMQGIS

So that you will get another point layer with the attributes of both point and polygon.

Then use expression "Z1" - "Z" to subtract Z values and store it in separate field

Final Attribute Table

Values that are in Negative range are the points that are having less Z value when compared to covered polygon. '0' value denotes the point and polygon are having same Z value.

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