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jsf_reader.m
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jsf_reader.m
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## Copyright (c) 2017 OceanScan - Marine Systems & Technology, Lda.
##
## This file is subject to the terms and conditions defined in file
## 'COPYING', which is part of this source code package.
##
## Author: Ricardo Martins <rasm@oceanscan-mst.com>
## Keywords: jsf sonar ping
## usage: PING = jsf_reader(FD)
##
## Read one ping from the JSF file specified by the file descriptor
## FD. This code is based on the information given in the document "JSF
## Data File Description Rev. 1.20".
##
## Return values:
## - Structure with ping metadata and raw data.
## - 0 if the end of file was reached while parsing a frame.
##
## If a parsing error is encountered an error will be raised.
function ping = jsf_reader(fd),
persistent saved_ping = 0;
% We have a saved ping, return that.
if isstruct(saved_ping)
saved_ping = 0;
ping = saved_ping;
return;
end
while (!feof(fd)),
ping = jsf_read_ping(fd);
if !isstruct(ping),
% Not sonar data.
if ping == 0,
continue;
end
% Incomplete frame (i.e., end of file reached while parsing).
if ping == 1,
ping = 0;
return;
end
end
% Read next ping.
saved_ping = jsf_read_ping(fd);
% Next ping contains the missing channel.
if ping.number == saved_ping.number && ping.cfreq == saved_ping.cfreq,
ping.data_stbd = saved_ping.data_stbd;
saved_ping = 0;
end
return;
end
end
function ping = jsf_read_ping(fd),
persistent last_ping = struct();
header_bytes = fread(fd, 16, "*uint8");
if size(header_bytes) != 16,
ping = 1;
return;
end
header = jsf_decode_message_header(header_bytes);
payload_bytes = fread(fd, header.payload_size, "*uint8");
if size(payload_bytes) != header.payload_size,
ping = 1;
return;
end
if header.type == 80,
ping = jsf_decode_sonar_data(payload_bytes, header.channel);
return;
end
ping = 0;
end
function header = jsf_decode_message_header(bytes),
marker = typecast(bytes([1:2]), "uint16");
if marker != 0x1601,
error("jsf: invalid message marker: %04X\n", marker);
end
header = struct();
header.version = bytes(3);
header.type = typecast(bytes([5:6]), "uint16");
header.subsys = bytes(8);
header.channel = bytes(9);
header.payload_size = typecast(bytes([13:16]), "uint32");
end
function ping = jsf_decode_sonar_data(bytes, channel),
ping = struct();
msbs = double(typecast(bytes([17:18]), "uint16"));
lsbs = double(typecast(bytes([19:20]), "uint16"));
% Time.
seconds = double(typecast(bytes([1:4]), "uint32"));
millis = double(typecast(bytes([201:204]), "uint32"));
ping.time = seconds + mod(millis, 1000.0) / 1000.0;
% Channel.
ping.channel = channel;
% Ping number.
ping.number = typecast(bytes([9:12]), "uint32");
% Longitude.
ping.lon = double(typecast(bytes([81:84]), "int32")) / 34377467.707849;
% Latitude.
ping.lat = double(typecast(bytes([85:88]), "int32")) / 34377467.707849;
% Depth.
ping.depth = double(typecast(bytes([137:140]), "int32")) / 1000.0;
% Altitude.
ping.alt = double(typecast(bytes([145:148]), "int32")) / 1000.0;
% Heading.
ping.heading = double(typecast(bytes([173:174]), "uint16")) / 100.0;
% Roll.
ping.pitch = double(typecast(bytes([175:176]), "int16")) * 180 / 32768;
% Pitch.
ping.roll = double(typecast(bytes([177:178]), "int16")) * 180 / 32768;
% Speed.
ping.speed = ((double(typecast(bytes([195:196]), "int16"))) / 10) * 0.54444444444;
% Number of samples.
num_samples = double(typecast(bytes([115:116]), "uint16"));
ping.num_samples = bitor(num_samples, bitshift(bitand(msbs, 0xf00), 8));
% Range.
sample_interval = double(typecast(bytes([117:120]), "uint32"));
ping.range = ((sample_interval / 1e9) * num_samples * 1500) / 2;
% Transmit pulse starting frequency.
sfreq = double(typecast(bytes([127:128]), "uint16"));
sfreq = bitor(sfreq, bitshift(bitand(msbs, 0xf), 16)) * 10;
% Transmit pulse ending frequency.
efreq = double(typecast(bytes([129:130]), "uint16"));
efreq = bitor(efreq, bitshift(bitand(msbs, 0xf0), 12)) * 10;
% Trasmit pulse center frequency.
ping.cfreq = sfreq + ((efreq - sfreq) / 2.0);
% Weighted data samples.
weight_factor = 2^-double(typecast(bytes([169:170]), "int16"));
data = double(typecast(bytes([241:end]), "uint16")) * weight_factor;
if channel == 0,
ping.data_port = data;
else
ping.data_stbd = data;
end
end