[opendtv] Re: The Challenge

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Thu, 24 May 2007 20:47:45 -0400

John,

I took your given times, and I created correct and valid <system_time> values.

I showed you exactly the method I used to arrive at those times. I gave you references to all of the web resources I used so you could do what any scientist does when verifying someone else's claim: repeat the experiment for themselves.

Much more than a though experiment, John, I did what you asked me to do to the best of my feeble abilities. You gave me times, and asked for <system_time> values. I think you were surprised that I even tried to answer your questions.

I also gave you a time, and asked you what you thought should be the valid <system_time> value. I know my example was right, because the starting time in UTC, and the ending <system_time> value came straight out of A/65C Annex D Section 7 Page 125.

Paul Freeman took another example from Mark Eyer's book, starting with a current time of day as 30 December 2001 13:00:00 UTC, and ending up with a <system_time> value of 0x2959D25D.

He worked through the problem using a website that gives the number of days between dates, and he came up with the same <system_time> value as Mark Eyer did. Does my technique also do that? Let's find out, shall we?

1) - Convert UTC to GPS time by adding the then current GPS_UTC offset value of 13 = 30 December 2001 13:00:13 UTC

2) - Plug in that date and time into Unix time stamp generator. Unix time stamp = 1009717213

3) - Subtract the Unix to GPS offset to get GPS seconds = 693752413

4) - Convert decimal to hex   <system_time> = 0x2959D25D

It worked. Again. That now confirms my method by two independent sources: The authors of A/65C Annex D Part 7, and Mark Eyer. That's also two independent methods (mine and Paul Freeman's) that uses GPS time to arrive at a <system_time> variable.

If you now want line by line computer code to do the same process just to re-prove the obvious yet again, then you're barking up the wrong tree. I am not a programmer and I never claimed to be. But that doesn't change the underlying facts.

This whole three day drawn out mess that has wasted over 10 of my hours arguing with you both on and off the OpenDTV list was simply because I said:

"<system_time> is expressed in GPS seconds."

I showed you that exact phrase in A/65C, Annex D, Part 7. I've pointed you to the definition of GPS time and the definition of UTC time so that there would be no mistake as to which is which.

Even the quote from Mary Eyer's book that Paul posted used the phrase "GPS seconds."

Please continue to insist that <system_time> is expressed as a UTC time. You are a light in the wilderness, John, when all around you are in the GPS dark.

John


----- Original Message ----- From: "johnwillkie" <johnwillkie@xxxxxxxxxxxxx>

No, you did a thought problem which is the start. I want the math; I trust
my interpretation, I trust my code, I want to see yours.

John Willkie




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