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Bruce Rowen wrote:
<blockquote cite="mid455A0FAF.8060201@aoc.nrao.edu" type="cite">Barry
Clark wrote:
<br>
<blockquote type="cite">There's a lot of content here, and I suspect
I'll have much more to say
<br>
when I've had time to do some work on these (I'm a bit tied up at the
<br>
moment in my other hat as scheduling officer). However, a couple of
remarks that occurred to me on a rather cursory reading.
<br>
<br>
1. Number of derivatives. We are working with two derivatives
<br>
at the moment. This seems to work pretty well for VLA antennas
tracking
<br>
translunar objects. (And the code can be easily changed to handle NMA
antennas.) The cases that probably require more (VLBI and satelite
tracking) have not had any serious design work done on them, so it's a
little unclear how we want to handle them. I strongly suspect that
they also will turn out to have a number of derivatives set by the
application, not something decided on the fly. My preference would be
that the number of derivatives be moved to a setup message, not sent
with every delay model.
<br>
(Presuming that it's needed at all, that it's inconvenient to just use
<br>
whatever arrives.)
<br>
<br>
2. Double. Why the preference for a hex encoded double, instead of
the
<br>
native 'double' form? (Just in case somebody decided to read one of
these
<br>
godawful things.)
<br>
<blockquote type="cite">Each coefficient is 64 bit (8 byte)
floating-point number encoded as hexBinary.
<br>
</blockquote>
<br>
</blockquote>
<br>
As a partial answer to #1 & #2, the coefficient encoding is nicely
compact and XML-able when all coefficients are encoded in
<br>
hexBinary. As part of the XML, an attribute specifying the length
(number of coefficients) is handy.
<br>
</blockquote>
<small>After some discussion here in DRAO we came to conclusion that,
at least for the testing, it would be useful to have readable format
for the coefficients (derivatives). Can we agree to use ASCII encoded
double as defined by the XML Schema Recommendations:<br>
<a class="moz-txt-link-freetext" href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/datatypes.html#double">http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/datatypes.html#double</a><br>
<br>
When the full system is deployed we can switch to optimized format if
we find that "verbose" models are generating to much traffic. <br>
And, in the spirit of "readability", I will keep the number of
derivatives in the model (for now).</small><br>
<blockquote cite="mid455A0FAF.8060201@aoc.nrao.edu" type="cite"><br>
<blockquote type="cite">3. Timestamps. We work internaly in a
double precision MJD and fraction
<br>
system (LSB is about one microsecond). Converting that to ISO 8601
form is easy of course, but I rather suspect that you also will be
working in some similar system internally, and it might save a few a
little bother at both ends just to send that.
<br>
</blockquote>
<br>
Internally our time is in seconds since the "epoch" with a time
resolution of 10ms. These are internally carried in
<br>
two unsigned integers (32 bits) as that works very nicely with the OS.
<br>
</blockquote>
<small>One of the decision from the face-to-face meeting was that time
in the XML messages is always UTC displayed as defined by ISO 8601. <br>
<br>
<br>
Sonja </small><br>
<br>
<blockquote cite="mid455A0FAF.8060201@aoc.nrao.edu" type="cite">
<blockquote type="cite">4. Delays. Who organizes the delay center?
Do I send numbers which might
<br>
be negative, or should I add something to them to make them always
positive?
<br>
If so, what?
<br>
</blockquote>
<br>
TBD, but my feeling is the correlator is "dumb" in the sense it doesn't
care about signs or offsets from its delay buffer
<br>
"center" (If the delay buffer center is somehow tied to the array delay
center). My only concern (the correlator speaking here) is that the
delay never exceeds the buffer range.
<br>
<br>
-Bruce
<br>
<br>
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</blockquote>
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</blockquote>
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