def deinterleave_array(ndarray: numpy.ndarray, offset: int,
step: int) -> numpy.ndarray:
"""
Extracts a single channel type from an interleaved array.
An interleaved channel contains multiple channel types in a single payload. This is useful for situations where
a sensor produces several values for a single timestamp. For example, a GPS will produce a LATITUDE, LONGITUDE,
ALTITUDE, and SPEED values with every update. An interleaved channel is an encoding that encodes multiple channel
types into a single payload.
Every channel has a field channel_types that list the channel types contained within the payload. For a GPS sensor,
the channel_types array would look like [LATITUDE, LONGITUDE, ALTITUDE, SPEED]. The location of the channel type
in channel_types determines the offset into the payload and the length of channel_types determines the step size.
As such, a GPS channel payload would contain the following values:
[LAT0, LNG0, ALT0, SPD0, LAT1, LNG1, ALT1, SPD1, ..., LATn, LNGn, ALTn, SPDn]
This function will "deinterleave" the encoding and provide an array of a single channel type.
:param ndarray: Interleaved array.
:param offset: Offset into the array.
:param step: The step size.
:return: A numpy array of a single channel type.
"""
if offset < 0 or offset >= len(ndarray):
raise exceptions.ReaderException(
"offset {} out of range [{},{})".format(offset, 0, len(ndarray)))
if offset >= step:
raise exceptions.ReaderException(
"offset {} must be smaller than step {}".format(offset, step))
if step <= 0 or step > len(ndarray):
raise exceptions.ReaderException("step {} out of range [{},{})".format(
step, 0, len(ndarray)))
if len(ndarray) % step != 0:
raise exceptions.ReaderException(
"step {} is not a multiple of {}".format(step, len(ndarray)))
# pylint: disable=C1801
if len(ndarray) == 0:
return empty_array()
return ndarray[offset::step]
def payload_median(self) -> numpy.float64:
"""Returns the median of this channel's payload.
:return: The median of this channel's payload.
"""
payload_values = self.payload_values()
if len(payload_values) <= 0:
raise exceptions.ReaderException("Can't obtain median value of empty array")
median = numpy.median(self.payload_values())
if isinstance(median, numpy.ndarray):
return median[0]
elif isinstance(median, numpy.float64):
return median
else:
raise exceptions.ReaderException("Unknown type %s" % str(type(median)))
def get_value_std(self, channel_type: int) -> float:
"""
Returns the standard deviation value for a single channel type.
:param channel_type: The channel type to extract the std from.
:return: The standard deviation.
"""
idx = self.channel_index(channel_type)
if idx < 0 or len(self.value_stds) == 0:
raise exceptions.ReaderException("std DNE, is the payload empty?")
return self.value_stds[idx]
def get_value_mean(self, channel_type: int) -> float:
"""
Returns the mean value for a single channel type.
:param channel_type: The channel type to extract the mean from.
:return: The mean value.
"""
idx = self.channel_index(channel_type)
if idx < 0 or len(self.value_means) == 0:
raise exceptions.ReaderException("mean DNE, is the payload empty?")
return self.value_means[idx]
def interleave_arrays(arrays: typing.List[numpy.ndarray]) -> numpy.ndarray:
"""
Interleaves multiple arrays together.
:param arrays: Arrays to interleave.
:return: Interleaved arrays.
"""
if len(arrays) < 2:
raise exceptions.ReaderException(
"At least 2 arrays are required for interleaving")
if len(set(map(len, arrays))) > 1:
raise exceptions.ReaderException("all arrays must be same size")
total_arrays = len(arrays)
total_elements = sum(map(lambda array: array.size, arrays))
interleaved_array = numpy.empty((total_elements, ), dtype=arrays[0].dtype)
for i in range(total_arrays):
interleaved_array[i::total_arrays] = arrays[i]
return interleaved_array
def lz4_decompress(buf: bytes) -> bytes:
"""
Decompresses an API 900 compressed buffer.
:param buf: The buffer to decompress.
:return: The uncompressed buffer.
"""
uncompressed_size = calculate_uncompressed_size(buf)
if uncompressed_size <= 0:
raise exceptions.ReaderException(
"uncompressed size [{}] must be > 0".format(uncompressed_size))
return lz4.block.decompress(
buf[4:], uncompressed_size=calculate_uncompressed_size(buf))
def get_metadata(metadata: typing.List[str], k: str) -> str:
"""
Given a meta-data key, extract the value.
:param metadata: List of metadata to extract value from.
:param k: The meta-data key.
:return: The value corresponding to the key or an empty string.
"""
if len(metadata) % 2 != 0:
raise exceptions.ReaderException(
"metadata list must contain an even number of items")
idx = safe_index_of(metadata, k)
if idx < 0:
return ""
return metadata[idx + 1]
def get_metadata_as_dict(metadata: typing.List[str]) -> typing.Dict[str, str]:
"""
Since the metadata is inherently key-value, it may be useful to turn the metadata list into a python dictionary.
:param metadata: The metadata list.
:return: Metadata as a python dictionary.
"""
if not metadata:
return {}
if len(metadata) % 2 != 0:
raise exceptions.ReaderException(
"metadata list must contain an even number of items")
metadata_dict = {}
metadata_copy = metadata.copy()
while len(metadata_copy) >= 2:
metadata_key = metadata_copy.pop(0)
metadata_value = metadata_copy.pop(0)
if metadata_key not in metadata_dict:
metadata_dict[metadata_key] = metadata_value
return metadata_dict
