Compute zero-mean values for polygon regions of interest (ROI) and count pixels below a threshold (default threshold: mean, can be adjusted by an offset). This model was developed for agricultural field trials (ROI were plots) but can be used in other contexts, too.

Inputs: * ROI polygon layer (regions of interest, e.g. field trial plots) * single band image (e.g. surface model, vegetation index) * threshold offset to adjust default mean

The algorithm computes the mean of each ROI, substracts it from the input and thresholds values below (mean+threshold_offset).

Useful to compare relative differences within ROIs.

Atttention: this model converts the inputs to a common metric CRS (UTM, EPSG:25832), this is hardcoded and needs to be changed, if you want to use different one.