Add missing sampling_offset_time for EK60 & set EK60/80 beam_direction_x/y/z to nan as needed

[emiliom]

• sampling_offset_time is missing from EK60! I've added it. See #1097
• Set EK60/80 beam_direction_x/y/z to nan when all 3 are zero

[codecov-commenter]

Codecov Report

Merging #1114 (fae819e) into dev (6671fec) will decrease coverage by 0.42%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev    #1114      +/-   ##
==========================================
- Coverage   78.24%   77.83%   -0.42%     
==========================================
  Files          65       18      -47     
  Lines        6255     2950    -3305     
==========================================
- Hits         4894     2296    -2598     
+ Misses       1361      654     -707     

Flag	Coverage Δ
unittests	77.83% <100.00%> (-0.42%)	:arrow_down:

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Files Changed	Coverage Δ
echopype/convert/set_groups_ek60.py	93.02% <100.00%> (+0.28%)	:arrow_up:
echopype/convert/set_groups_ek80.py	97.56% <100.00%> (+0.04%)	:arrow_up:

... and 49 files with indirect coverage changes

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[emiliom]

Thanks!

Thinking about it again, the (0, 0, 0) combination is invalid, but all combinations that do not give a length=1 vector would also be invalid, but I could see how people might put a non-normalized vector in the (x,y,z), so the check has to handle something else or determine whether to normalize the length by default, etc, etc.

Agreed. More generally, echopype doesn't do any conversion or checking (other than what I just added) of the ek60 and ek80 datagram values that are fed into beam_direction_x/y/z. That may be true for other parameters, too.