Advanced settings for peeled images

Peeloff origin

First, it is possible to change the origin relative to which the peeling-off, and therefore the image extent, are defined. This is set to (0., 0., 0.) by default, but you can change it using:

image.set_peeloff_origin((x, y, z))

where x, y, and z are floating-point values giving the cartesian coordinates of the peeloff origin. This can be used for example when doing radiative transfer calculations on a simulation, in order to create images centered on different sources.

Inside observers

It is also possible to specify that the images should be calculated from the point of view of an observer that is inside the coordinate grid, rather than at infinity. For example, if you are calculating a model of the Milky-Way Galaxy, you could place yourself at the position of the Sun using:

from hyperion.util.constants import kpc
image.set_inside_observer((8.5 * kpc, 0., 0.))

Note that in this case, the peeloff origin cannot be set, and the image limits, rather than being in cm, should be given in degrees on the sky. Note also that, like sky coordinates, the x range of the image limits should be inverted. For example:

image.set_image_limits(65., -65., -1., 1.)

will produce an image going from l=65 to l=-65, and from b=-1 to b=1. Note that only images (not SEDs) can be computed for inside observers.

Image depth

Finally, it is possible to restrict the depth along the line of sight from which photons should be included, with the default being:

image.set_depth(-np.inf, np.inf)

The minimum and maximum depth are measured in cm. For standard images, the depth is taken relative to the plane passing through the origin of the peeling-off. For images calculated for an observer inside the grid, the default is:

image.set_depth(0., np.inf)

where the depth is measured relative and away from the observer.

Note that in this mode, the optical depth used to calculate the peeling off is the total optical depth to the observer, not just the optical depth in the slab considered. The slab is only used to determine which emission or scattering events should be included in the image.