On 10/16/12 7:56 PM, "Jack de Valpine"
<je...@visarc.com<mailto:je...@visarc.com>> wrote:
Hi Tim,
I cannot test this right now, however I do know that it is possible for
gendaylit to fail in select conditions. If I recall correctly, one is if the
direct normal radiance is zero (not the case here). There are other cases where
it fails more dramatically, which is what you are facing I believe. In this
case I think that the thing to do is re-use a previous value from the data set
(eg the previous hour).
Unfortunately, what you really need to do is actually "test" if gendaylit is
going to produce valid output prior to actually getting the output. This can be
done by evaluating the result of:
gendaylit $myArgs > /dev/null 2>&1
which in your case would be
gendaylit 7 19 14.500 -W 924 65 -a 34.3 -o 116.17 -m 120 > /dev/null 2>&1
Assuming your are processing a complete weather file then you need to test
every time step that is not definitively at night, so that you can catch any
time steps that case an error for gendaylit and then do something in those
places.
This has been a constant headache for us as well, as we are trying to use
gendaylit in the OpenStudio annual simulation stuff. We do a test like Jack has
illustrated above, again cribbing from Axel's excellent tutorials. We have
found that bad sky descriptions can still be written (or nothing), and our test
can miss some. The error reporting in gendaylit seems inconsistent. We try to
scan for all the warnings/errors we have seen coming from gendaylit like so:
gendaylit_command = "gendaylit -ang #{tsSolarAlt} #{tsSolarAzi} -L
#{tsDirectNormIllum} #{tsDiffuseHorIllum} 2>&1"
tempIO = IO.popen(gendaylit_command)
gendaylit_output = tempIO.readlines.to_s
tempIO.close
tempSky = true
if /[wW]arning/.match(gendaylit_output) or
/[eE]rror/.match(gendaylit_output) or /valid/.match(gendaylit_output) or
/[cC]heck/.match(gendaylit_output) or /skyclearness/.match(gendaylit_output)
tempSky = false
End
…we fall back on gensky if found. Andy McNeil proposes scanning for a really
tiny file (one of the failure modes for gendaylit is it writes a blank file
with no errors generated). I implemented that in Ruby with the tempfile class,
but obviously I did a poor job because the tempfiles were not being properly
killed, so I took that out for now. But I do need to beef up this error
checking as we'd prefer to use gendaylit.
- Rob
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