Module simplify
Simplify or linearize a path of LatLon points.
Each of the 4 simplify functions is based on a different
algorithm and produces different, simplified results in (very) different
run times for the same path:
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Function simplify1 eliminates points with edge lengths
shorter than the given tolerance.
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Function simplifyRDP implements the
Ramer-Douglas-Peucker (RDP) algorithm, iteratively finding the
point farthest from each path edge. Original RDP exhaustively
searches the most distant point in each iteration, modified
RDP stops at the first point exceeding the distance tolerance.
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Function simplifyRW uses the Reumann-Witkam (RW)
method, sliding a "pipe" over each path edge, removing all
subsequent points within the pipe radius, up to the first point
outside the pipe.
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Function simplifyVW provides the Visvalingam-Whyatt
(VW) method using the area of the triangle formed by three neigboring
points. Original VW removes only a single point per iteration,
modified VW eliminates all points with a triangular area not
exceeding the tolerance in each iteration.
Keyword argument shortest of functions simplifyRDP and simplifyRW specifies 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) edge through both points.
Keyword argument radius of all fuctions is set to
the mean earth radius in meter, conventionally. Other units
may be used, provided that radius and tolerance are specified in the same
units.
Use keyword argument indices=True in any function
to return a list of indices of simplified point instead of the
simplified points with 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 by
eliminating any points closer together than the given distance
tolerance. |
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simplifyRDP(points,
distance=0.001,
radius=6371008.771415,
shortest=False,
indices=False,
modified=False,
**options)
Ramer-Douglas-Peucker (RDP) simplification of a path of
LatLon points by eliminating any points too close
together or closer to an edge than the given distance
tolerance. |
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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 by eliminating any points too close
together or within the given pipe tolerance along an edge. |
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simplifyVW(points,
area=0.001,
radius=6371008.771415,
indices=False,
attr=None,
modified=False,
**options)
Visvalingam-Whyatt (VW) simplification of a path of
LatLon points by eliminating any points too close or
with a triangular area not exceeding the given area tolerance
squared. |
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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 by
eliminating any points closer together than the given distance
tolerance.
- Arguments:
points - Iterable with the path points (LatLon[]).distance - Tolerance (meter, same units as
radius).radius - Mean earth radius (meter, conventionally).indices - If True, return points indices
instead of the simplified points (bool).options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]) or
points indices.
- Raises:
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simplifyRDP (points,
distance=0.001,
radius=6371008.771415,
shortest=False,
indices=False,
modified=False,
**options)
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Ramer-Douglas-Peucker (RDP) simplification of a path of
LatLon points by eliminating any points too close together
or closer to an edge than the given distance tolerance.
- Arguments:
points - Iterable with the path points (LatLon[]).distance - Tolerance (meter, same units as
radius).radius - Mean earth radius (meter, conventionally).shortest - If True, use the shortest otherwise the
perpendicular distance (bool).indices - If True, return points indices
instead of the simplified points (bool).modified - If True, use the modified RDP method
(bool), see the note.options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]) or
points indices.
- Raises:
Note:
The original RDP method exhaustively searches for the
point with the largest distance (resulting in complexity O(n**2) with n is the number
of points). The modified RDP
method stops at the first point farther than the
distance tolerance, significantly reducing the
run time (but producing results different from the original
RDP method).
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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 by eliminating any points too close together
or within the given pipe tolerance along an edge.
- Arguments:
points - Iterable with the path points (LatLon[]).pipe - Pipe radius, half-width (meter, same units as
radius).radius - Mean earth radius (meter, conventionally).shortest - If True, use the shortest otherwise the
perpendicular distance (bool).indices - If True, return points indices
instead of the simplified points (bool).options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]) or
points indices.
- Raises:
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simplifyVW (points,
area=0.001,
radius=6371008.771415,
indices=False,
attr=None,
modified=False,
**options)
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Visvalingam-Whyatt (VW) simplification of a path of
LatLon points by eliminating any points too close or with a
triangular area not exceeding the given area tolerance
squared.
- Arguments:
points - Iterable with the path points (LatLon[]).area - Tolerance (meter, same units as
radius).radius - Mean earth radius (meter, conventionally).indices - If True, return points indices
instead of the simplified points (bool).attr - Optional, points attribute to save the area
value (str).modified - If True, use the modified VW method
(bool), see the note.options - Optional keyword arguments passed thru to function pygeodesy.equirectangular4. - Returns:
- Simplified points (
LatLon[]) or
points indices.
- Raises:
AttributeError - An attr isinvalid for Numpy2
points.LimitError - Lat- and/or longitudinal delta exceeds the
limit, see function pygeodesy.equirectangular4.ValueError - Tolerance area or radius
too small.
Note:
The original VW method exhaustively searches for the
point with the smallest triangular area (resulting in
complexity O(n**2) with n
the number of points). The modified
VW 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).
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