To obtain an ordered numpy array of stands connected to the DP system at a particular station:
1 2 3 | from lsl.common import stations
lwa1 = stations.lwa1
stands = lwa1.getStands()
|
This retrieves a lsl.common.stations.LWAStation instance for LWA-1 built using the SSMIF file included with the LSL release. To get the list of stands corresponding to a different SSMIF file:
1 2 3 | from lsl.common import stations
lwa = stations.parseSSMIF('your_ssmif.txt')
stands = lwa1.getStands()
|
Although the stand list is useful, it is more useful to have a list of lsl.common.stations.Antenna instances. This provide much more information about the station setup (stand, FEE, position, etc.) than the simple stands list. To get this list:
1 2 3 | from lsl.common import stations
lwa1 = stations.lwa1
antennas = lwa1.getAntennas()
|
It should be noted that this function returned the antennas in order of DP digitizer number so that it is easier to convert digitizer numbers to something useful.
LSL provides several interfaces for working with the contents of a MCS meta-data tarball without having to manually extract all of the files and identify the necessary files. For example, the SSMIF file contained in the tarball can be converted to a lsl.common.stations.LWAStation instance using:
1 2 | from lsl.common import metabundle
lwa1 = metabundle.getStation('obs_metadata.tar.gz', ApplySDM=True)
|
lsl.common.metabundle.getStation() hides all of the details of extracting the SSMIF file from the tarball and converting it to a LWAStation instance. The ApplySDM flag indicates the the station dynamic MIB file should be used to update the various antenna status values for the station based on their condition as defined by MCS.
The lsl.common.metabundle module also provides access to the actual settings (tuning, filter code, etc.) used for the individual observations. The lsl.common.metabundle.getSessionDefinition() function creates a filled lsl.common.sdf.Project instance containing all of the session-wide and observation- specific values used by MCS. This function also updates the individual lsl.common.sdf.Observation instances to include attributes storing the op. code name (for matching is data file names), the outcome status, and any MCS message relating to that observation:
1 2 3 4 5 | from lsl.common import metabundle
project = metabundle.getSessionDefinition('obs_metadata.tar.gz')
nObs = len(project.sessions[0].observations)
OpCode0 = project.sessions[0].observations[0].opcode
Outcome0 = project.sessions[0].observations[0].outcome
|
The above code reads all of the session and observation related files inside the meta-data tarball and creates a SDF Project instance. The individual observations are stored in the project.sessions[0].observations list.
Once a list of lsl.common.stations.Antenna instances has been retrieved, it is easy to get stand positions:
1 2 3 4 | xyz = numpy.zeros((3,))
xyz[0] = antennas[0].stand.x
xyz[1] = antennas[0].stand.y
xyz[2] = antennas[0].stand.z
|
Where x refers to the east-west difference of the antenna from the station’s center post, y refers to the north-south distance from the station’s center post, and z to the height above the center post. All of the coordinates are in meters.
The list of lsl.common.stations.Antenna also makes it easy to find out the cable delay for a particular antennas:
dly = antennas[0].cable.getDelay(49e6)
By default, delays are computed in seconds and the input frequencies are in Hz. The delays can be automatically converted to nanoseconds by setting the ns keyword to True.
Similarly, the cable loss for a particular antenna can be found:
los = antennas[0].cable.getGain(49e6)
The lsl.correlator.uvUtils.computeUVW() function allows for uvw coordinates to be computed for a all baselines formed from a collection of stands for a particular hour angle, declination, and frequency:
1 2 3 4 5 | from lsl.common import stations
from lsl.correlator import uvUtils
lwa1 = stations.lwa1
antennas = lwa1.getAntennas()
uvw = uvUtils.computeUVW(antennas, HA=1.0, dec=65.0, freq=50e6, IncludeAuto=True)
|
The above code block computes the uvw coordinates at 50 MHz for all stands used on JD 2,455,548.38 for an object at an hour angle of 1 hour and a declination of +65 degrees. The returned list of uvw coordinates will also include entries for autocorrelations. The order of the baselines is given by the function lsl.correlator.uvUtils.getBaselines().
The lsl.misc.geodesy modules includes functions to retrieve earth orientation parameters (EOP; x, y, and UT1-UTC) for a given modified Julian Date (MJD) or MJD range. To retrieve the parameters as a lsl.misc.geodesy.EOP object, use:
1 2 3 4 5 | from lsl import astro
from lsl.misc import geodesy
jd = 2455548.38787
mjd = jd - astro.MJD_OFFSET
eop = geodesy.getEOP(mjd)
|
For multiple MJDs, use lsl.misc.geodesy.getEOPRange() to return a list of EOPs, one for each day:
1 2 3 4 5 6 7 8 9 | from lsl import astro
from lsl.misc import geodesy
jd1 = 2455548.38787
jd2 = 2455552.38787
mjd1 = jd1 - astro.MJD_OFFSET
mjd2 = jd2 - astro.MJD_OFFSET
eops = geodesy.getEOPRange(mjd1, mdj2)
for eop in eops:
print str(eop)
|