As it looks like you are the one who created the poi_visibilities.txt file, maybe you can help me a bit.
Could you tell me what is the relationship between ultramar/turbo and uni-mart/ultramar?
Could you elaborate on the meaning of the trailing zeros? Sometimes the 1st 0 is replaced by 3000, 5000 or 15000 and the 2nd 0 by 500

2 lines from your poi_visibilities.txt file:

Petrol_StationUltramar|turbo|0|0
Petrol_StationUni-Mart|ultramar|0|0