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20051108: IDV extract image time

>From: "Valentijn Venus" <address@hidden>
>Organization: ITC
>Keywords: 200511081635.jA8GZT7s003999 IDV jython formula

Hi Valentijn-

>I'm trying to extend on your "IDV extract image time" example.
>Eventually I would like to  evaluating the image observation time (of an
>image object in an imageSequence) against the sunset hour for that
>particular day. We added a function that makes the hour of sunset
>available (UTC) available for a particular day in the year. If the image
>object is younger than the hour of sunset, then a certain bandmath
>formula (Land surface temperature) is used, and otherwise a nighttime
>LST algorithm should be used. I'm struggeling to get the two time
>objects in the same format in order to evaluate them:
>
>Traceback (innermost last):
>  File "<string>", line 1, in ?
>  File "<string>", line 22, in getImageTime
>AttributeError: 'None' object has no attribute 'setFormatPattern'

The problem is that you define dateTime as None and then
try to set the format pattern on it.  Essentially, you get
a NullPointerException.  If you comment out the :

    dateFormat = dateTime.setFormatPattern("yyyy")

then you'll not get the exception.  You set the pattern later and
that's what it will use.

Instead of calling:

     dateTime.setFormatPattern("yyyy")
     year = dateTime.toString()

I would call:

(set this before the loop)
     tz = TimeZone.getTimeZone("GMT");

then inside the loop:

     year = dateTime.formattedString("yyyy", tz)

When you are calling setFormatPattern, that sets a static
variable for any DateTime object.  The latter only formats
the output.

I couldn't test this because I don't have the atof
function, but hopefully you'll get the idea.

>The function looks like this:
>
>import java
>
>def getImageTime(imagesequence, i):
>   import sys;
>   sys.add_package('visad.meteorology');
>   sys.add_package('GridUtil');
>   #import java.text.SimpleDateFormat;
>   #import java.util.TimeZone;
>
>   from java.text import SimpleDateFormat
>   from visad import DateTime
>   from visad.meteorology import ImageSequence
>   from visad.meteorology import SingleBandedImage
>
>   lineValuesA = imagesequence.getFloats()
>   newd = imagesequence.clone()
>   dateTime = None
>   dateFormat = dateTime.setFormatPattern("yyyy")
>
>   if isinstance(imagesequence, ImageSequence):
>       sbi = imagesequence.getImage(int(i))
>       dateTime = sbi.getStartTime()
>   elif isinstance(imagesequence, SingleBandedImage):
>       dateTime = imagesequence.getStartTime()
>   for i in xrange(imagesequence.getDomainSet().getLength()):
>      dateTime.setFormatPattern("yyyy")
>      year = dateTime.toString()
>      lineValuesA[0][i] = atof(year)
>   newd.setSamples(lineValuesA)
> 
>   return newd 
>
>Any ideas?

Alternatively, you could use dateTime.getValue() to get
the seconds, multiply that by 1000 to get milliseconds
and create a Java Date object and use that for your
calculations if you are more familiar with manipulating
Java Date objects.

Don Murray
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