webbpsf_ext.coords.gen_sgd_offsets

webbpsf_ext.coords.gen_sgd_offsets(sgd_type, slew_std=5, fsm_std=2.5, rand_seed=None)[source]

Create a series of x and y position offsets for a SGD pattern. This includes the central position as the first in the series. By default, will also add random movement errors using the slew_std and fsm_std keywords. Returned values in arcsec.

Parameters

  • sgd_type (str) – Small grid dither pattern. Valid types are ‘9circle’, ‘5box’, ‘5diamond’, ‘3bar’, ‘5bar’, ‘5miri’, and ‘9miri’ where the first four refer to NIRCam coronagraphic dither positions and the last two are for MIRI coronagraphy.

  • fsm_std (float) – One-sigma accuracy per axis of fine steering mirror positions. This provides randomness to each position relative to the nominal central position. Ignored for central position. Values should be in units of mas.

  • slew_std (float) – One-sigma accuracy per axis of the initial slew. This is applied to all positions and gives a baseline offset relative to the desired mask center. Values should be in units of mas.

  • rand_seed (int) – Input a random seed in order to make reproduceable pseudo-random numbers.