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In a QField project, I have two layers:
When an agent wishes to record a point on a parcel in the field, if the agent's geographical position does not correspond to the location of the parcel where he is, the entry will not be executed.
Unfortunately, QGIS does not treat geometry like any other attribute of a feature class - it should, but it doesn't.
A possible workaround is to create a field, e.g. a uuid field. Do not use the UUID generator widget type, use a text edit. Make the widget uneditable. Set constraints of the field to NOT NULL and 'enforce constraint'.
Under default value use overlay_intersects() expression or similar to check the current point feature is within your target polygon. Be aware that depending on how you use overlay_intersects() it may return a boolean or an array. (Check out the syntax and options for overlay_intersects() in the manual). Assuming your point can be within any polygon of your target layer, you can simply use overlay_intersects('myTargetLayer'), which returns a boolean: true if it is inside a polygon, false if not. You can then put this in a case statement something like
case
when overlay_intersects('myTargetLayer') then uuid()
else null
end
If the expression returns null, then you will not be able to save the feature.
EDIT: Screenshots of it working. In this case I am using tree_pt as my point layer and tgtnote_ar as my polygon layer. For 'tree_pt' I have a text field with default set to
case
when overlay_intersects('tgtnote_ar') then uuid
else null
end
(Note: the 'when' clause, could be written as when overlay_intersects('tgtnote_ar') = True then uuid, but the '= True' is implicit.)
I have constraints set to 'Not null' and 'Enforce not null constraint' checked.
Here is a short GIF of it working. First two attempts at plotting a point are outside of a polygon: the feature form opens but can't be saved. Third attempt is inside a polygon. The feature form opens and the save button is enabled - I save the feature.
