Multi-Resolution Modeling

Multi-Resolution Modeling (MRM) is a modeling technology that creates a family of models that represent the same phenomenon or a set of questions at more than two different resolutions. The fine-grained spatial scales could cover corridors, roads, and lane representations, and the temporal resolution refers to the time interval (or time stamps) at which the dynamic state of the model is updated, typically ranging from days to seconds. Each type of model (macroscopic, mesoscopic, or microscopic) has its own advantages and disadvantages, and represents a trade-off between scales and resolution levels. The ultimate goal of MRM is to seamlessly integrate models with different temporal and spatial resolutions, while the focus of the cross-resolution approach is to bridge the gaps between macroscopic and microscopic levels, so as to provide strong theoretical support and deeper insights for both levels.

The osm2gmns package adopts the GMNS standard and further extends it to a inherently consistent multi-resolution network modeling standard. With a single line of code, osm2gmns can help users generate corresponding mesoscopic and microscopic networks for any given macroscopic networks in GMNS format, enabling practitioners and researchers to carry out various studies on transportation planning, designing, optimization, simulation, and computation under different spatial granularities. In this section, we mainly talk about the three levels of transportation network representation.

Multi-resolution network representation

Macroscopic Network

• node.csv

Field	Type	Required?	Comments
name	string
node_id	int	yes	unique key
osm_node_id	string or int		corresponding node id in osm data
osm_highway	string		point type in osm data
zone_id	int
ctrl_type	enum		signal; null
node_type	string
activity_type	string		defined by adjacent links
is_boundary	enum		-1: boundary node only with incoming links; 0: no; 1: boundary node only with outgoing links; 2: boundary node with both incoming and outgoing links
x_coord	double	yes	WGS 84 is used in osm
y_coord	double	yes	WGS 84 is used in osm
intersection_id	int		nodes belonging to one complex intersection have the same id
poi_id	int		id of the corresponding poi
notes	string

• link.csv

A link is an edge in a network, defined by the nodes it travels from and to. It may have associated geometry information^[2]. Similar to node.csv, We also added several new attributes to the link file. Detailed link data dictionary is listed below.

Field	Type	Required?	Comments
name	string
link_id	int	yes	unique key
osm_way_id	string or int		corresponding way id in osm data
from_node_id	int	yes
to_node_id	int	yes
dir_flag	enum		1: forward, -1: backward, 0:bidirectionial
length	float		unit: meter
lanes	int
free_speed	float		unit: kilometer/hour
capacity	float		unit: veh/hr/lane
link_type_name	string
link_type	int
geometry	Geometry		wkt
allowed_uses	enum		auto, bike, walk
from_biway	bool		1: link created from a bidirectional way, 0: not
is_link	bool		1: link connecting two roads, 0: not

There are two optional files including movement.csv and segement.csv that follow the exact same format as defined in the GMMS standard. Readers can check the GMNS website for details.

In addition to the above files defined in the GMNS standard, osm2gmns can also produce poi.csv files where point of interest information is stored. Detailed poi data dictionary is listed below.

Field	Type	Required?	Comments
name	string
poi_id	int	yes	unique key
osm_way_id	string or int		corresponding way id in osm data
osm_relation_id	string or int		corresponding relation id in osm data
building	string		building tag in osm data
amenity	string		amenity tag in osm data
way	string		way tag in osm data
geometry	Geometry	yes	wkt
centroid	Geometry		wkt
area	float		area of the poi. unit: square meter
area_ft2	float		area of the poi. unit: square feet

Mesoscopic Network

Compared to the original macroscopic network, the mesoscopic network has more detailed information of the intersections. In the mesoscopic network, the research team expanded each intersection represented by a node in the macroscopic network. The team built a connector link for each intersection movement to facilitate intersection modeling, especially for signalized intersections.

Macroscopic and mesoscopic networks have different link-level coding schemes. Macroscopic networks often represent a road segment between two adjacent intersections as a link; however, lane changes sometimes occur within a link, especially when close to intersections. Changes in the number of lanes result in capacity changes, but the link attributes cannot properly reflect these changes. This situation may bring inconvenience or even potential errors when performing network modeling. In the GMNS standard, the comma-separated values (CSV) file, segment.csv, stores lane changes. The research team split and converted each link with lane changes from a macroscopic network to multiple mesoscopic links so that each mesoscopic link has a homogeneous capacity.

• node.csv

Field	Type	Required?	Comments
node_id	int	yes	unique key
zone_id	int
x_coord	double	yes	WGS 84 is used in osm
y_coord	double	yes	WGS 84 is used in osm
macro_node_id	int		id of its parent macroscopic node
macro_link_id	int		id of its parent macroscopic link
activity_type	string
is_boundary	enum		-1: boundary node only with incoming links; 0: no; 1: boundary node only with outgoing links

• link.csv

A link is an edge in a network, defined by the nodes it travels from and to. It may have associated geometry information^[2]. Similar to node.csv, We also added several new attributes to the link file. Detailed link data dictionary is listed below.

Field	Type	Required?	Comments
link_id	int	yes	unique key
from_node_id	int	yes
to_node_id	int	yes
dir_flag	enum		1: forward, -1: backward, 0:bidirectionial
length	float		unit: meter
lanes	int
free_speed	float		unit: kilometer/hour
capacity	float		unit: veh/hr/lane
link_type_name	string
link_type	int
geometry	Geometry		wkt
macro_node_id	int		id of its parent macroscopic node
macro_link_id	int		id of its parent macroscopic link
mvmt_txt_id	enum		NBL, NBT, NBR, NBU, SBL, SBT, SBR, SBU, EBL, EBT, EBR, EBU, WBL, WBT, WBR, WBU
allowed_uses	enum		auto, bike, walk

Microscopic Network

In the Maryland case study, microscopic networks used a lane-by-lane, cell-based representation. Instead of a conceptual line segment, lanes represented each link. The research team further discretized lanes into small cells to accurately describe vehicle motion status when moving on the road. The team also created changing cells to enable vehicles to switch trajectories between lanes. Users can customize the length of cells to accommodate different modeling needs.

• node.csv

Field	Type	Required?	Comments
node_id	int	yes	unique key
zone_id	int
x_coord	double	yes	WGS 84 is used in osm
y_coord	double	yes	WGS 84 is used in osm
meso_link_id	int		id of its parent mesoscopic link
lane_no	int		start from 1 from inner side to outer side
is_boundary	enum		-1: boundary node only with incoming links; 0: no; 1: boundary node only with outgoing links

• link.csv

A link is an edge in a network, defined by the nodes it travels from and to. It may have associated geometry information^[2]. Similar to node.csv, We also added several new attributes to the link file. Detailed link data dictionary is listed below.

Field	Type	Required?	Comments
link_id	int	yes	unique key
from_node_id	int	yes
to_node_id	int	yes
dir_flag	enum		1: forward, -1: backward, 0:bidirectionial
length	float		unit: meter
lanes	int
free_speed	float		unit: kilometer/hour
capacity	float		unit: veh/hr/lane
link_type_name	string
link_type	int
geometry	Geometry		wkt
macro_node_id	int		id of its parent macroscopic node
macro_link_id	int		id of its parent macroscopic link
meso_link_id	int		id of its parent mesoscopic link
cell_type	enum		1: traveling cell, 2: lane changing cell
additional_cost	float
lane_no	int		start from 1 from inner side to outer side
mvmt_txt_id	enum		NBL, NBT, NBR, NBU, SBL, SBT, SBR, SBU, EBL, EBT, EBR, EBU, WBL, WBT, WBR, WBU
allowed_uses	enum		auto, bike, walk

^[1] https://github.com/zephyr-data-specs/GMNS/blob/master/Specification/Node.md

^[2] https://github.com/zephyr-data-specs/GMNS/blob/master/Specification/Link.md