optionally map level's level_index to GeoJSON Z coordinate

With a customisable mapping function?

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With this MBTA example, such a feature would really make sense!

pathway_id,from_stop_id,to_stop_id,facility_id,pathway_mode,is_bidirectional,length,wheelchair_length,traversal_time,wheelchair_traversal_time,stair_count,max_slope,pathway_name,pathway_code,signposted_as,instructions
grnst-004,door-grnst-main,node-grnst-fareunpaid,,1,0,11.8872000,11.8872000,,,,,"Green Street - Woolsey Sq, Green St, Amory St to Unpaid side of fare gates",,All trains,
grnst-005,node-grnst-fareunpaid,door-grnst-main,,1,0,11.8872000,11.8872000,,,,,"Unpaid side of fare gates to Green Street - Woolsey Sq, Green St, Amory St",,"Woolsey Square, Green Street, Amory Street, Franklin Park/Zoo",
grnst-006,node-grnst-fareunpaid,node-grnst-farepaid,,6,0,,,,,,,Unpaid side of fare gates to Paid side of fare gates,,,
grnst-007,node-grnst-farepaid,node-grnst-fareunpaid,,7,0,,,,,,,Paid side of fare gates to Unpaid side of fare gates,,,
grnst-008,node-grnst-farepaid,node-grnst-844-lobby,,1,0,10.3632000,10.3632000,,,,,Paid side of fare gates to Top of Elevator 844,,Elevator,
grnst-009,node-grnst-844-lobby,node-grnst-farepaid,,1,0,10.3632000,10.3632000,,,,,Top of Elevator 844 to Paid side of fare gates,,,
grnst-010,node-grnst-farepaid,node-grnst-131-lobby,,1,0,7.9248000,7.9248000,,,,,Paid side of fare gates to Top of Escalator 131,,,
grnst-011,node-grnst-131-lobby,node-grnst-farepaid,,1,0,7.9248000,7.9248000,,,,,Top of Escalator 131 to Paid side of fare gates,,,
grnst-012,node-grnst-farepaid,node-grnst-stairs-lobby,,1,0,7.9248000,7.9248000,,,,,Paid side of fare gates to Top of stairs,,,
grnst-013,node-grnst-stairs-lobby,node-grnst-farepaid,,1,0,7.9248000,7.9248000,,,,,Top of stairs to Paid side of fare gates,,,
grnst-014,node-grnst-844-lobby,node-grnst-844-platform,844,5,0,,,46,46,,,Top of Elevator 844 to Bottom of Elevator 844,844,Platform,
grnst-015,node-grnst-844-platform,node-grnst-844-lobby,844,5,0,,,46,46,,,Bottom of Elevator 844 to Top of Elevator 844,844,Lobby,
grnst-016,node-grnst-131-platform,node-grnst-131-lobby,131,4,0,,,25,,,,Bottom of Escalator 131 to Top of Escalator 131,131,,
grnst-017,node-grnst-stairs-lobby,node-grnst-stairs-platform,,2,0,,,,,-32,,Top of stairs to Bottom of stairs,,,
grnst-018,node-grnst-stairs-platform,node-grnst-stairs-lobby,,2,0,,,,,32,,Bottom of stairs to Top of stairs,,,
grnst-019,node-grnst-844-platform,70003,,1,0,15.2400000,15.2400000,,,,,Bottom of Elevator 844 to Orange Line (Oak Grove),,Inbound to Oak Grove via Downtown Crossing and State,
grnst-020,70003,node-grnst-844-platform,,1,0,71.0184000,71.0184000,,,,,Orange Line (Oak Grove) to Bottom of Elevator 844,,Elevator,
grnst-021,node-grnst-131-platform,70003,,1,0,12.1920000,12.1920000,,,,,Bottom of Escalator 131 to Orange Line (Oak Grove),,Inbound to Oak Grove via Downtown Crossing and State,
grnst-022,70003,node-grnst-131-platform,,1,0,65.5320000,65.5320000,,,,,Orange Line (Oak Grove) to Bottom of Escalator 131,,Exit to street,
grnst-023,node-grnst-stairs-platform,70003,,1,0,12.1920000,12.1920000,,,,,Bottom of stairs to Orange Line (Oak Grove),,Inbound to Oak Grove via Downtown Crossing and State,
grnst-024,70003,node-grnst-stairs-platform,,1,0,67.6656000,67.6656000,,,,,Orange Line (Oak Grove) to Bottom of stairs,,Exit to street,
grnst-025,node-grnst-844-platform,70002,,1,0,15.2400000,15.2400000,,,,,Bottom of Elevator 844 to Orange Line (Forest Hills),,Outbound to Forest Hills,
grnst-026,70002,node-grnst-844-platform,,1,0,71.0184000,71.0184000,,,,,Orange Line (Forest Hills) to Bottom of Elevator 844,,Elevator,
grnst-027,node-grnst-131-platform,70002,,1,0,12.1920000,12.1920000,,,,,Bottom of Escalator 131 to Orange Line (Forest Hills),,Outbound to Forest Hills,
grnst-028,70002,node-grnst-131-platform,,1,0,65.5320000,65.5320000,,,,,Orange Line (Forest Hills) to Bottom of Escalator 131,,Exit to street,
grnst-029,node-grnst-stairs-platform,70002,,1,0,12.1920000,12.1920000,,,,,Bottom of stairs to Orange Line (Forest Hills),,Outbound to Forest Hills,
grnst-030,70002,node-grnst-stairs-platform,,1,0,67.6656000,67.6656000,,,,,Orange Line (Forest Hills) to Bottom of stairs,,Exit to street,

stop_id,stop_code,stop_name,stop_desc,platform_code,platform_name,stop_lat,stop_lon,zone_id,stop_address,stop_url,level_id,location_type,parent_station,wheelchair_boarding,municipality,on_street,at_street,vehicle_type
place-grnst,,Green Street,,,,42.310525,-71.107414,,"150 Green St, Jamaica Plain, MA",https://www.mbta.com/stops/place-grnst,,1,,1,Boston,,,
door-grnst-main,,"Green Street - Woolsey Sq, Green St, Amory St","Green Street - Woolsey Sq, Green St, Amory St",,,42.310556,-71.107519,,,,level_in_street,2,place-grnst,1,Boston,,,
node-grnst-131-lobby,,Green Street,Green Street - Top of Escalator 131,,,42.310388,-71.107617,,,,level_in_street,3,place-grnst,1,Boston,,,
node-grnst-131-platform,,Green Street,Green Street - Bottom of Escalator 131,,,42.310297,-71.107676,,,,level_-1_platform,3,place-grnst,1,Boston,,,
node-grnst-844-lobby,,Green Street,Green Street - Top of Elevator 844,,,42.310370,-71.107662,,,,level_in_street,3,place-grnst,1,Boston,,,
node-grnst-844-platform,,Green Street,Green Street - Bottom of Elevator 844,,,42.310370,-71.107662,,,,level_-1_platform,3,place-grnst,1,Boston,,,
node-grnst-farepaid,,Green Street,Green Street - Paid side of fare gates,,,42.310462,-71.107597,,,,level_in_street,3,place-grnst,1,Boston,,,
node-grnst-fareunpaid,,Green Street,Green Street - Unpaid side of fare gates,,,42.310462,-71.107597,,,,level_in_street,3,place-grnst,1,Boston,,,
node-grnst-stairs-lobby,,Green Street,Green Street - Top of stairs,,,42.310406,-71.107673,,,,level_in_street,3,place-grnst,1,Boston,,,
node-grnst-stairs-platform,,Green Street,Green Street - Bottom of stairs,,,42.310317,-71.107743,,,,level_-1_platform,3,place-grnst,1,Boston,,,

level_id,level_index,level_name,level_elevation
level_-1_platform,-1.0000000,Platform,
level_in_street,0.0000000,On street,