get_lt
- acstools.utils_calib.get_lt(hdr)
Obtain the LTV and LTM keyword values.
Note that this returns the values just as read from the header, which means in particular that the LTV values are for one-indexed pixel coordinates.
LTM keywords are the diagonal elements of MWCS linear transformation matrix, while LTV’s are MWCS linear transformation vector (1-indexed).
Note
Translated from
calacs/lib/getlt.c
.- Parameters:
hdr (obj) – Extension header.
- Returns:
ltm, ltv –
(LTM1_1, LTM2_2)
and(LTV1, LTV2)
. Values are(1, 1)
and(0, 0)
if not found, to accomodate reference files with missing info.- Return type:
- Raises:
ValueError – Invalid LTM* values.