Module simplify
Simplify or linearize a path.
Each of the simplify functions is based on a different
algorithm and produces different, simplified results in (very) different
run times for the same path of LatLon points.
Function simplify1 eliminates points based on edge lengths
shorter than a given tolerance.
The functions simplifyRDP and simplifyRDPm use the original, respectively modified
Ramer-Douglas-Peucker (RDP) algorithm, iteratively finding the
point farthest from each path edge. The difference is that function simplifyRDP exhaustively searches the most distant point
in each iteration, while modified simplifyRDPm stops at the first point exceeding the
distance tolerance.
Function simplifyRW use the Reumann-Witkam method, sliding
a "pipe" over each path edge, removing all subsequent points
within, closer than the pipe radius up to the first point outside the
pipe.
Functions simplifyVW and simplifyVWm are based on the original, respectively
modified Visvalingam-Whyatt (VW) method using the area of the
triangle formed by three neigboring points. Function simplifyVW removes only a single point per iteration,
while modified simplifyVWm eliminates in each iteration all points with
a triangular area not exceeding the tolerance.
Functions simplifyRDP, simplifyRDPm and simplifyRW provide keyword argument shortest to
specify of the distance between a point and a path edge. If
True, use the shortest distance to the path edge or
edge points, otherwise use the perpendicular distance to the
extended line through both path edge points.
Keyword argument radius of all fuctions is set to
the mean earth radius in meter. Other units can be used,
provided that the radius and tolerance are always specified in the same
units.
Use keyword argument indices=True in any function
to return a list of simplified point indices instead of the
simplified points. The first and last index are always the first and last
original index.
Finally, any additional keyword arguments options
to all functions are passed thru to function pygeodesy.equirectangular4 to specify the distance
approximation.
To process NumPy arrays containing rows of lat-,
longitude and possibly other values, use class Numpy2LatLon to wrap the NumPy array into
on-the-fly-LatLon points. Pass the Numpy2LatLon instance to any simplify function
and the returned result will be a NumPy array containing the
simplified subset, a partial copy of the original NumPy
array. Use keyword argument indices=True to return a
list of array row indices inlieu of the simplified array subset.
See:
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simplify1(points,
distance=0.001,
radius=6371008.771415,
indices=False,
**options)
Basic simplification of a path of LatLon points. |
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simplifyRDP(points,
distance=0.001,
radius=6371008.771415,
shortest=False,
indices=False,
**options)
Ramer-Douglas-Peucker (RDP) simplification of a path of
LatLon points. |
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simplifyRDPm(points,
distance=0.001,
radius=6371008.771415,
shortest=False,
indices=False,
**options)
Modified Ramer-Douglas-Peucker (RDPm) simplification of a path
of LatLon points. |
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simplifyRW(points,
pipe=0.001,
radius=6371008.771415,
shortest=False,
indices=False,
**options)
Reumann-Witkam (RW) simplification of a path of
LatLon points. |
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simplifyVW(points,
area=0.001,
radius=6371008.771415,
attr=None,
indices=False,
**options)
Visvalingam-Whyatt (VW) simplification of a path of
LatLon points. |
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simplifyVWm(points,
area=0.001,
radius=6371008.771415,
attr=None,
indices=False,
**options)
Modified Visvalingam-Whyatt (VWm) simplification of a path of
LatLon points. |
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__all__ = _ALL_LAZY.simplify
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simplify1 (points,
distance=0.001,
radius=6371008.771415,
indices=False,
**options)
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Basic simplification of a path of LatLon points.
Eliminates any points closer together than the given distance
tolerance.
- Arguments:
points - Path points (LatLon[]).distance - Tolerance (meter, same units as
radius).radius - Mean earth radius (meter).indices - If True, return the simplified point indices instead
of the simplified points (bool).options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]).
- Raises:
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simplifyRDP (points,
distance=0.001,
radius=6371008.771415,
shortest=False,
indices=False,
**options)
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Ramer-Douglas-Peucker (RDP) simplification of a path of
LatLon points.
Eliminates any points too close together or closer to an edge than the
given distance tolerance.
This RDP method exhaustively searches for the point with
the largest distance, resulting in worst-case complexity O(n**2) where n is the number of
points.
- Arguments:
points - Path points (LatLon[]).distance - Tolerance (meter, same units as
radius).radius - Mean earth radius (meter).shortest - If True, use the shortest otherwise the
perpendicular distance (bool).indices - If True, return the simplified point indices instead
of the simplified points (bool).options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]).
- Raises:
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simplifyRDPm (points,
distance=0.001,
radius=6371008.771415,
shortest=False,
indices=False,
**options)
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Modified Ramer-Douglas-Peucker (RDPm) simplification of a path
of LatLon points.
Eliminates any points too close together or closer to an edge than the
given distance tolerance.
This RDPm method stops at the first point farther than
the given distance tolerance, significantly reducing the run time (but
producing results different from the original RDP
method).
- Arguments:
points - Path points (LatLon[]).distance - Tolerance (meter, same units as
radius).radius - Mean earth radius (meter).shortest - If True, use the shortest otherwise the
perpendicular distance (bool).indices - If True, return the simplified point indices instead
of the simplified points (bool).options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]).
- Raises:
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simplifyRW (points,
pipe=0.001,
radius=6371008.771415,
shortest=False,
indices=False,
**options)
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Reumann-Witkam (RW) simplification of a path of
LatLon points.
Eliminates any points too close together or within the given
pipe tolerance along an edge.
- Arguments:
points - Path points (LatLon[]).pipe - Pipe radius, half-width (meter, same units as
radius).radius - Mean earth radius (meter).shortest - If True, use the shortest otherwise the
perpendicular distance (bool).indices - If True, return the simplified point indices instead
of the simplified points (bool).options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]).
- Raises:
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simplifyVW (points,
area=0.001,
radius=6371008.771415,
attr=None,
indices=False,
**options)
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Visvalingam-Whyatt (VW) simplification of a path of
LatLon points.
Eliminates any points too close together or with a triangular area not
exceeding the given area tolerance squared.
This VW method exhaustively searches for the single point
with the smallest triangular area, resulting in worst-case complexity O(n**2) where n is the number of
points.
- Arguments:
points - Path points (LatLon[]).area - Tolerance (meter, same units as
radius).radius - Mean earth radius (meter).attr - Optional, points attribute to save the area value
(str).indices - If True, return the simplified point indices instead
of the simplified points (bool).options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]).
- Raises:
AttributeError - If an attr is specified for Numpy2
points.LimitError - Lat- and/or longitudinal delta exceeds the
limit, see function pygeodesy.equirectangular4.ValueError - Tolerance area or radius
too small.
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simplifyVWm (points,
area=0.001,
radius=6371008.771415,
attr=None,
indices=False,
**options)
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Modified Visvalingam-Whyatt (VWm) simplification of a path of
LatLon points.
Eliminates any points too close together or with a triangular area not
exceeding the given area tolerance squared.
This VWm method removes all points with a triangular area
below the tolerance in each iteration, significantly reducing the run
time (but producing results different from the original VW
method).
- Arguments:
points - Path points (LatLon[]).area - Tolerance (meter, same units as
radius).radius - Mean earth radius (meter).attr - Optional, points attribute to save the area value
(str).indices - If True, return the simplified point indices instead
of the simplified points (bool).options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]).
- Raises:
AttributeError - If an attr is specified for Numpy2
points.LimitError - Lat- and/or longitudinal delta exceeds the
limit, see function pygeodesy.equirectangular4.ValueError - Tolerance area or radius
too small.
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