# NIRISSForwardColumnGrismDispersion¶

class jwst.transforms.models.NIRISSForwardColumnGrismDispersion(orders, lmodels=None, xmodels=None, ymodels=None, theta=None, name=None, meta=None)[source]

Bases: astropy.modeling.core.Model

This model calculates the wavelengths for horizontally dispersed NIRISS grism data.

The dispersion polynomial is relative to the input x,y pixels in the direct image for a given wavelength.

Parameters
• orders (list) – The list of orders which are available to the model.

• xmodels (list[tuple]) – The list of tuple(models) for the polynomial model in x

• ymodels (list[tuple]) – The list of tuple(models) for the polynomial model in y

• lmodels (list) – The list of models for the polynomial model in wavelength.

• theta (float) – Angle [deg] - defines the NIRISS filter wheel position

Notes

Given the x,y, source location, order, it returns the tuple of x,y,wavelength,order on the dispersed image. It also requires FWCPOS from the image header, this is the filter wheel position in degrees.

Attributes Summary

Methods Summary

 __call__(*inputs[, model_set_axis, …]) Evaluate this model using the given input(s) and the parameter values that were specified when the model was instantiated. evaluate(x, y, x0, y0, order) Return the valid pixel(s) and wavelengths given center x,y and lam

Attributes Documentation

fittable = False
linear = False
n_inputs = 5
n_outputs = 4
standard_broadcasting = False

Methods Documentation

__call__(*inputs, model_set_axis=None, with_bounding_box=False, fill_value=nan, equivalencies=None, inputs_map=None, **new_inputs)

Evaluate this model using the given input(s) and the parameter values that were specified when the model was instantiated.

evaluate(x, y, x0, y0, order)[source]

Return the valid pixel(s) and wavelengths given center x,y and lam

Parameters
• x0 (int,float) – Source object x-center

• y0 (int,float) – Source object y-center

• x (int,float) – Input x location

• y (int,float) – Input y location

• order (int) – Spectral order to use

• theta (float) – input filter wheel rotation angle in degrees

Returns

• x, y, lambda, order, in the direct image for the pixel that was

• specified as input using the wavelength l and spectral order

Notes

There’s spatial dependence for NIRISS as well as rotation for the filter wheel