switchyard from elegant to opal z value

[moellep]

When I use switchyard to convert output from an elegant sim to opal, it looks like the z value isn't what opal expects.

For example, using this elegant output file (from the Sirepo Los Alamos Proton Storage Ring example).
run_setup.output.sdds.gz

from rsbeams.rsdata import switchyard
sw = switchyard.Switchyard()
sw.read('run_setup.output.sdds', 'elegant')
sw.write('opal.dat', 'opal')

If I look at the first lines of opal.dat, the z value is around 139.36, rather than something closer to 0.

1000
-6.340713545584865688e-07 -8.766794044966910791e-05 -3.501193557502712281e-04 -8.219311411194487292e-05 1.393657565044637181e+02 8.494205066937067228e-01
-3.035502267016218497e-05 -8.404898146293522112e-05 3.509641817225703101e-04 2.626942294232129908e-06 1.393657075909387402e+02 8.494207845133487922e-01

If I try to run an opal sim with that input file, it fails silently almost immediately. If I subtract the mean(z) from that value, it works OK, but that probably isn't the right thing to do.