Here are some examples of using tmatch2
:
stilts tmatch2 in1=obs_v.xml in2=obs_i.xml out=obs_iv.xml \ matcher=sky values1="ra dec" values2="ra dec" params="2"
stilts tmatch2 survey.fits ifmt2=csv mycat.csv \ icmd1='addskycoords fk4 fk5 RA1950 DEC1950 RA2000 DEC2000' \ matcher=skyerr \ params=10 values1="RA2000 DEC2000 POS_ERR" values2="RA DEC 0" \ join=2not1 omode=count
skyerr
matcher is
used, which takes account of this; the third entry in the
values1
parameter is the POS_ERR column (in arcsec).
Since the second input table has no positional uncertainty information,
0 is used as the third entry in values2
.
The params
gives a rough idea of the scale of the object
separations, but its value does not affect the result.
The join type is 2not1
, which means the output table
will only contain those entries which are in the second input table
but not in the first one.
The output table is not stored, but the number of rows it contains
(the number of objects represented in the CSV file but not the survey)
is written to the screen.
stilts tmatch2 ifmt1=ascii ifmt2=ascii in1=cat-a.txt in2=cat-b.txt \ matcher=2d values1='X Y' values2='X Y' params=5 join=1and2 \ suffix1=_a suffix2=_b \ ocmd='addcol XDIFF X_a-X_b; addcol YDIFF Y_a-Y_b' \ ocmd'keepcols "XDIFF YDIFF"' omode=stats
suffix*
parameters describe
how the input X and Y columns are to be renamed to avoid duplicate
column names in the output table.
To this result are added two new columns,
representing the X and Y positional
difference between the rows from one input table and those from the other.
The keepcols
filter then throws all the other columns away,
retaining only these difference columns.
The final two-column table is not stored anywhere,
but (omode=stats
)
statistics including mean and standard deviation
are calculated on its columns and displayed to the screen.
Having done all this, you can examine the average X and Y differences
between the two input tables for matched rows, and if they differ
significantly from zero, you can conclude that there is a systematic
error between the positions in the two input files.
stilts tmatch2 in1=mgc.fits in2=6dfgs.xml join=1and2 find=all \ matcher=sky+1d params='3 0.5' \ values1='ra dec bmag' values2='RA2000 DEC2000 B_MAG" \ out=pairs.fits
sky
and 1d
match criteria. This means that the only
rows which match are those which are
both within 3 arcsec of each other on the sky
and and within 0.5 blue magnitudes.
Note that for both the params
and the
values1
and values2
parameters,
the items for the sky
matcher (RA and DEC)
are listed first,
followed by those for the 1d
matcher (in this case,
blue magnitude).