MPO Connections:
Working with MPO Canopus
If you're also using MPO Canopus for your measuring images, you should be aware of some
interrelations between Connections and Canopus. This allows you to make the most of
Connections for astrometry and photometry.
When Canopus loads a FITS image, the format used by Connections, it attempts to use the
values saved under the OBJECT keyword and/or the OBJCTRA and OBJCTDEC keyword pair. If one
or both sets are found, then when Canopus generates a chart, it first tries to determine
the position of the object (if an asteroid). If it can’t, it uses the RA and
Declination values to center the chart.
By having the RA and Declination values available, Canopus can automatically generate
and match a chart to the image for measuring reference stars and the target.
Canopus and the OBJECT Field
Canopus attempts to interpret the OBJECT field in the following ways.
Example: A1417
If the value starts with ‘A’ and is followed by a number, the ‘A’
is removed and Canopus attempts to convert the rest of the value to a number.
If that succeeds, the assumption is that the object is a numbered asteroid and chart
center is based on the computed position using the date and time in the FITS header,
adjusted as necessary by the configuration settings to Universal Date/Time.
If the conversion to a number does not succeed but the OBJCTRA/DEC keywords have valid
entries, then Canopus uses those fields to center the chart.
Example: 1417
If the first and second characters are a number and there is no space in the value,
then Canopus attempts to convert the value to a number. It then proceeds as outlined in
Example 1.
Example: 1999 CZ1
If the first and second characters are numbers and there is a space in the value, the
assumption is that the value is an unpacked MPC designation. Canopus converts the value to
the packed form and then back to unpacked. If the original value and the returned unpacked
string are the same, then Canopus tries to find the asteroid in the MPC database and, if
found, proceeds as in the case of a numbered asteroid. If the packed-to-unpacked test
fails or the asteroid is not in the MPC database but the OBJCTRA/DEC fields have valid
values, the chart is centered on the position in those fields.
Example: Ceres
Canopus attempts to do a name lookup in the MPC data. If found, then Canopus proceeds
as in the case of a numbered asteroid. If not found but there are valid entries for the
OBJCTRA/DEC keywords, the chart is centered on the position indicated in those fields.
How does this all fit into Connections? When you set the Default Base Name in the
Configuration settings or Arg2 of a TakeImage command in a script, the OBJECT field is set
with one or the other value. Thus, if you properly set one and/or both, Canopus can
automatically determine which asteroid you were working, numbered or unnumbered, and
generate the chart based on the asteroid’s position at the time that the image was
taken.
This has the particular advantage that when using the AutoMeasure feature of Canopus,
where it matches a chart to the image (as the AutoMeasure method does in Connections),
then Canopus can try to measure the position of the asteroid for you. If the chart is
based on position only, no such attempt is made.
Canopus and the OBJCTRA/OBJCTDEC Fields
If the OBJECT field does not contain a valid entry as defined above, then Canopus uses
the settings in these two fields. Connections sets these fields for you.
Whenever you take an image with the telescope linked, the RA and Declination reported
by the scope are recorded into the FITS header under these two keywords. This is
particularly important if you are working a target other than an asteroid since, most
likely, the OBJECT field will not be interpreted as an asteroid.
If there is no telescope linked, you can still have Connections insert the position
into the FITS header by using the "RA/DEC from GoTo" checkbox in the
Configuration settings. This means that the RA and Declination are taken from the two
fields used to manually slew the scope to a given position. Naturally, you need to be sure
these two fields are set correctly before taking each image.
If all else Fails
If for some reason your image(s) don’t have entries that can be properly
interpreted by Canopus, you can use the Image Header editor in either Connections or
Canopus to enter values into the appropriate fields. This could be rather tedious if you
have a lot of images so your best bet is to follow the guidelines above to the maximum
benefit of using Canopus and Connections together.
Valid Formats for OBJCTRA and OBJCTDEC
The entries for these two fields in the FITS header must be in the following format so
that Canopus can convert them correctly.
OBJCTRA HHxMM[xSS[.ss]]
OBJCTDEC ħDDxMM[xSS[.ss]]
Where ‘x’ represents either a space or colon ( : ) and the entries within the
square brackets are optional. For declination, you must enter the sign ( +
or – ) as appropriate, i.e., the sign symbol is not optional. |
