coordinates

Methods for dealing with coordinates.

hsr4hci.coordinates.cartesian2polar(position, frame_size)

Convert a position in Cartesian coordinates (in pixels) to astronomical polar coordinates.

Parameters:

• position (Tuple[float, float]) – A tuple (x, y) containing a position in Cartesian coordinates.

• frame_size (Tuple[int, int]) – A 2-tuple (width, height) of integers specifying the size of the frame that we are working with.

Returns:

A 2-tuple (separation, angle), where the separation is a Quantity in pixels, and angle is a Quantity in radian. The angle uses the astronomical convention for polar coordinates, that is, 0 is “up”, not “right” (unlike in mathematical polar coordinates).

Return type:

Tuple[Quantity, Quantity]

hsr4hci.coordinates.get_center(frame_size)

Using the frame size of an image, determine the precise position of its center in the usual coordinate system that we place on our data: The center of the pixel in the bottom left corner of the image is defined as (0, 0), so the bottom left corner of the image is located at (-0.5, -0.5).

This function is essentially a simplified port of the corresponding PynPoint function pynpoint.util.image.center_subpixel().

Parameters:

frame_size (Tuple[int, int]) – A tuple of integers (x_size, y_size) specifying the size of the images (in pixels).

Returns:

A tuple of floats, (center_x, center_y) containing the position of the center of the image.

Return type:

Tuple[float, float]

hsr4hci.coordinates.polar2cartesian(separation, angle, frame_size)

Convert a position in astronomical polar coordinates to Cartesian coordinates (in pixels).

Parameters:

• separation (Quantity) – Separation from the center (as a Quantity object that can be converted to pixels).

• angle (Quantity) – Angle, measured from the up = North direction (this corresponds to a -90° offset compared to “normal” polar coordinates), as a Quantity object that can be converted to degrees or radian.

• frame_size (Tuple[int, int]) – A 2-tuple (x_size, y_size) of integers specifying the size of the frame that we are working with.

Returns:

A 2-tuple (x, y) containing the Cartesian representation of the position specified by the (separation, angle) tuple. The Cartesian representation uses the astropy convention for the position of the origin, and the numpy convention for the order of the dimensions.

Return type:

Tuple[float, float]