peterlu14
109 lines
3.8 KiB
Python
109 lines
3.8 KiB
Python
"""
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The MIT License (MIT)
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Copyright (c) 2015 Olivier Devoisin
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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"""
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import math
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class LttbException(Exception):
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pass
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def largest_triangle_three_buckets(data, threshold):
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"""
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Return a downsampled version of data.
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Parameters
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----------
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data: list of lists/tuples
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data must be formated this way: [[x,y], [x,y], [x,y], ...]
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or: [(x,y), (x,y), (x,y), ...]
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threshold: int
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threshold must be >= 2 and <= to the len of data
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Returns
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-------
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data, but downsampled using threshold
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"""
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# Check if data and threshold are valid
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if not isinstance(data, list):
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raise LttbException("data is not a list")
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if not isinstance(threshold, int) or threshold <= 2 or threshold >= len(data):
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raise LttbException("threshold not well defined")
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for i in data:
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if not isinstance(i, (list, tuple)) or len(i) != 2:
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raise LttbException("datapoints are not lists or tuples")
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# Bucket size. Leave room for start and end data points
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every = (len(data) - 2) / (threshold - 2)
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a = 0 # Initially a is the first point in the triangle
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next_a = 0
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max_area_point = (0, 0)
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sampled = [data[0]] # Always add the first point
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for i in range(0, threshold - 2):
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# Calculate point average for next bucket (containing c)
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avg_x = 0
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avg_y = 0
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avg_range_start = int(math.floor((i + 1) * every) + 1)
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avg_range_end = int(math.floor((i + 2) * every) + 1)
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avg_rang_end = avg_range_end if avg_range_end < len(data) else len(data)
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avg_range_length = avg_rang_end - avg_range_start
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while avg_range_start < avg_rang_end:
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avg_x += data[avg_range_start][0]
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avg_y += data[avg_range_start][1]
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avg_range_start += 1
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avg_x /= avg_range_length
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avg_y /= avg_range_length
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# Get the range for this bucket
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range_offs = int(math.floor((i + 0) * every) + 1)
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range_to = int(math.floor((i + 1) * every) + 1)
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# Point a
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point_ax = data[a][0]
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point_ay = data[a][1]
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max_area = -1
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while range_offs < range_to:
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# Calculate triangle area over three buckets
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area = math.fabs(
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(point_ax - avg_x)
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* (data[range_offs][1] - point_ay)
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- (point_ax - data[range_offs][0])
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* (avg_y - point_ay)
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) * 0.5
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if area > max_area:
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max_area = area
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max_area_point = data[range_offs]
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next_a = range_offs # Next a is this b
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range_offs += 1
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sampled.append(max_area_point) # Pick this point from the bucket
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a = next_a # This a is the next a (chosen b)
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sampled.append(data[len(data) - 1]) # Always add last
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return sampled
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