unresolved¶
This module provides a class which implements an unresolved center finding RelNav technique along with a new meta class that adds concrete center-of-brightness to center-of-figure correction methods.
Description of the Technique¶
Unresolved center finding is applicable when you observe a target that is dominated by the point spread function of the
camera rather than by the geometry of the object. Typically this occurs when the apparent diameter of the object in
the image is less than 5-10 pixels. Because these targets are dominated by the camera point spread function,
GIANT treats unresolved bodies the same way that stars are treated. In fact, all of the same algorithms and functions
are used from the image_processing module as are used for extracting potential star locations from images.
First, the area around the expected location of the target body is searched for all groupings of pixels that exceed a
specified threshold. Then, as long as there is 1 and only 1 grouping of pixels above the threshold in the search
region, the sub-pixel center of brightness is extracted by using the specified fitting function (typically a 2D gaussian
or a moment algorithm. This is all done in the ImageProcessing.locate_subpixel_poi_in_roi() method from the
image processing class.
This routine is generally used during early approach to an object, or for extracting Celestial Navigation (CelNav) observations to known targets from the solar system. It does not apply once the target’s apparent diameter begins to exceed 5-10 pixels and will begin failing at that point.
Tuning¶
The primary control for tuning this technique is through the tuning of the
ImageProcessing.locate_subpixel_poi_in_roi() method. There are a number of tuning parameters
for this method and we direct you to its documentation for more details.
In addition, there are a few tuning parameters for the class itself.
The search region is controlled by the search_distance attribute. This should be an
integer which specifies half of the square region to search around the predicted center, such that a 2*
search_distance by 2* search_distance pixels of the
image will be searched.
In addition, Whether the phase correction is applied or not is controlled by the boolean flag
apply_phase_correction. The phase correction computation can be controlled using the
phase_correction_type and brdf attributes.
Use¶
This class is not typically not used directly by the user, but instead is
called from the RelativeOpNav class using the technique name of unresolved. For more details on using
this class directly, refer to the following class documentation. For more details on using this class through the
RelativeOpNav user interface refer to the relnav_class documentation.
Classes
This enumeration provides the possible phase correction methods to use to convert the observed center-of-brightness to a center of figure observation. |
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This class adds phase correction capabilities to RelNavEstimator. |
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This class implements GIANT's version of unresolved center finding for extracting bearing measurements to unresolved targets in an image. |