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.


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.


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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