String. Choosing an pof function, Options:
pof_function = c(pof_cables_04kv_pex, pof_cables_10kv_pex, pof_cables_10kv_oil,
pof_cables_60_30kv, pof_ohl_cond_50kv, pof_submarine_cables_10kv_oil,
pof_submarine_cables_10kv_pex, pof_submarine_cables_30_60kv_oil,
pof_submarine_cables_30_60kv_pex, pof_transformer_04_10kv, pof_building,
pof_serviceline, "Default").