Algorithm description Iso-Areas

Data Source: Stadt Wien – data.wien.gv.at

Iso-Area as Pointcloud (from Point)

The Iso-Area Pointcloud algorithms are the backbone of the QNEAT3 Iso-Area functionality. It queries the networks vertices inside a user-defined cost-range starting a single point that is chosen by the user. Doing so, the algorithm also accounts for entry-costs of the startpoints and adds it to the on-network cost. As a whole the vertices found inside the given cost-range amount to the Iso-Area Pointcloud. The output as vector points is especially useful when quering costs (eg. using the output in nearest-neighbor analysis)

#	Mandatory Parameters	Type	Info
1	Network Layer	Vector Layer	Geometry type must be LineString
2	Start Point (x, y)	Coordinate pair	obtain by clicking on map canvas
3	Size of Iso-Area	user input	dep. on strategy: max. distance / max. time(sec)
4	Optimization Criterion	Shortest \| Fastest	-
5	Pointcloud Layer	Output Vector Layer	-

Data Source: Stadt Wien – data.wien.gv.at

Iso-Area as Pointcloud (from Layer)

This algorithm extends the capabilities of his little brother above as it queries the networks vertices inside a user-defined cost-range starting from multiple points provided in a point vector layer. Doing so, the algorithm also accounts for entry-costs of the startpoints and assigns the nearest start-point ID to each vertex. As a whole the vertices found inside the given cost-range amount to the Iso-Area Pointcloud. The output as vector points is especially useful when quering costs (eg. using the output in nearest-neighbor analysis)

#	Mandatory Parameters	Type	Info
1	Network Layer	Vector Layer	Geometry type must be LineString
2	Startpoint Layer	Vector Layer	Geometry must be Point
3	Unique Point ID Field	Field	A unique identifier field for the startpoints (preferably Integer)
3	Size of Iso-Area	user input	dep. on strategy: max. distance / max. time(sec)
4	Optimization Criterion	Shortest \| Fastest	-
5	Pointcloud Layer	Output Vector Layer	-

Data Source: Stadt Wien – data.wien.gv.at

Iso-Area as Interpolation (from Point)

Warning: Algorithm will only work with data in projected coordinate systems (eg. no WGS84). This is due to a limitation of the QgsTinInterpolator class (see thread at gis.stackexchange.com).
You may use UTM-Coordinate zones matching your analysis area.

The Iso-Area as Interpolation algorithms take the Pointcloud approach a step further. It outputs an interpolated distance raster starting from a user-chosen point, applying the TIN-Interpolation method implemented in QGIS3 (QgsTinInterpolator). The resulting distance raster is especially useful in multi-criteria site-analysis that look at accessibility. It can be combined with fuzzy modeling methods.

#	Mandatory Parameters	Type	Info
1	Network Layer	Vector Layer	Geometry type must be LineString
2	Start Point (x, y)	Coordinate pair	obtain by clicking on map canvas
3	Size of Iso-Area	user input	dep. on strategy: max. distance / max. time(sec)
4	Optimization Criterion	Shortest \| Fastest	-
5	Interpolation Layer	Output Raster Layer	-

Data Source: Stadt Wien – data.wien.gv.at

Iso-Area as Interpolation (from Layer)

As the point-based interpolation algorithm, this one outputs an interpolated distance raster starting from multiple points provided by a vector layer, applying the TIN-Interpolation method implemented in QGIS3 (QgsTinInterpolator). The resulting distance raster is especially useful in multi-criteria site-analysis that look at accessibility. It can be combined with fuzzy modeling methods.

#	Mandatory Parameters	Type	Info
1	Network Layer	Vector Layer	Geometry type must be LineString
2	Startpoint Layer	Vector Layer	Geometry must be Point
3	Unique Point ID Field	Field	A unique identifier field for the startpoints (preferably Integer)
3	Size of Iso-Area	user input	dep. on strategy: max. distance / max. time(sec)
4	Optimization Criterion	Shortest \| Fastest	-
5	Interpolation Layer	Output Raster Layer	-

Data Source: Stadt Wien – data.wien.gv.at

Iso-Area as Contours (from Point)

The Iso-Area as Contours algorithm outputs contours (cost-break-lines) derived from an interpolated distance raster starting from a single points provided by a vector layer. For this it uses the matplotlib library, therefore the algorithm only is available when this library has been installed (see Installation and Setup). The contours are especially suited for visualization techniques of accessibility.

#	Mandatory Parameters	Type	Info
1	Network Layer	Vector Layer	Geometry type must be LineString
2	Start Point (x, y)	Coordinate pair	obtain by clicking on map canvas
3	Size of Iso-Area	user input	dep. on strategy: max. distance / max. time(sec)
4	Contour interval (distance or time value)	user input	dep. on strategy: max. distance / max. time(sec), determines number of contours in output.
5	Cell Size	user input	set higher for faster but more inacurate results
6	Optimization Criterion	Shortest \| Fastest	-
7	Interpolation Layer	Output Raster Layer	optional
8	Contour Layer	Output Vector Layer	-

Data Source: Stadt Wien – data.wien.gv.at

Iso-Area as Contours (from layer)

#	Mandatory Parameters	Type	Info
1	Network Layer	Vector Layer	Geometry type must be LineString
2	Start Point Layer	Vector Layer	Geometry must be Point
3	Size of Iso-Area	user input	dep. on strategy: max. distance / max. time(sec)
4	Contour interval (distance or time value)	user input	dep. on strategy: max. distance / max. time(sec), determines number of contours in output.
5	Cell Size	user input	set higher for faster but more inacurate results
6	Optimization Criterion	Shortest \| Fastest	-
7	Interpolation Layer	Output Raster Layer	optional
8	Contour Layer	Output Vector Layer	-

Data Source: Stadt Wien – data.wien.gv.at

Iso-Area as Polygon (from Point)

The Iso-Area as Polygon algorithm outputs filled polygons (spreding to cost-break-lines) derived from an interpolated distance raster starting from a single point. For this it uses the matplotlib library, therefore the algorithm only is available when this library has been installed (see Installation and Setup). The contours are especially suited for quering spatial objects that lie inside a specific driving distance or time range from multiple start points.

#	Mandatory Parameters	Type	Info
1	Network Layer	Vector Layer	Geometry type must be LineString
2	Start Point Layer	Vector Layer	Geometry must be Point
3	Size of Iso-Area	user input	dep. on strategy: max. distance / max. time(sec)
4	Contour interval (distance or time value)	user input	dep. on strategy: max. distance / max. time(sec), determines number of contours in output.
5	Cell Size	user input	set higher for faster but more inacurate results
6	Optimization Criterion	Shortest \| Fastest	-
7	Interpolation Layer	Output Raster Layer	optional
8	Polygon Layer	Output Vector Layer	-

Data Source: Stadt Wien – data.wien.gv.at

Iso-Area as Polygon (from Layer)

The Iso-Area as Polygon algorithm outputs filled polygons (spreding to cost-break-lines) derived from an interpolated distance raster starting from a multiple points provided by a vector layer. For this it uses the matplotlib library, therefore the algorithm only is available when this library has been installed (see Installation and Setup). The contours are especially suited for quering spatial objects that lie inside a specific driving distance or time range from multiple start points.

#	Mandatory Parameters	Type	Info
1	Network Layer	Vector Layer	Geometry type must be LineString
2	Start Point Layer	Vector Layer	Geometry must be Point
3	Size of Iso-Area	user input	dep. on strategy: max. distance / max. time(sec)
4	Contour interval (distance or time value)	user input	dep. on strategy: max. distance / max. time(sec), determines number of contours in output.
5	Cell Size	user input	set higher for faster but more inacurate results
6	Optimization Criterion	Shortest \| Fastest	-
7	Interpolation Layer	Output Raster Layer	optional
8	Polygon Layer	Output Vector Layer	-

#	Optional Parameters	Type	Info
1	Direction field	Field containing direction values	-
2	Value for forward direction	user input	input must be referenced to Direction field
3	Value for backward direction	user input	input must be referenced to Direction field
4	Value for both directions	user input	input must be referenced to Direction field
5	Default direction	Both Directions \| Forward Direction \| Backward Direction
6	Speed Field	Field containing speed values	must be numerical
7	Default speed	user input	(!) sets network entry- and exit-speed
8	Topology tolerance	user input	Tolerate gaps in network (crs units)