General
SPC has the ability to weight different inputs into the solution.
These are controls by the uncertainty values and by INIT_LITHOS.TXT
spacecraft position and pointing
One of the key goals of SPC is to provide a solution of the spacecraft's position for the optical navigation team. This is done by using autoregister on OpNav images in which landmarks are associated with an image and the 3D position of the image is determined by the covariance of the position vectors (i.e. find a solution that has the smallest error).
In general, our focus in on the relative position of the landmarks to the image, but there are other factors:
- WB: body -- The solution controlled by the landmarks
- WS: nominals SCOBJ -- The solution provided by the SPICE kernels.
- WC: nominals Pointing -- The pointing solution provided by the SPICE kernels.
- WL: limbs -- The solution controlled by the limb data (for images that have limbs, the position of the landmarks gives a strong constraint on where the spacecraft can be).
- WT: dynamics -- The other images that were taken before and after the image in question. The position should be along a similar arc as these observations.
INIT_LITHOS.TXT contains the variable PICWTS. Normally the value is one, meaning no extra weighting is use beyond the default values in SPC. However, if you want to increase (or decrease) the impact that one of these constrains have, you can increase (or decrease) the number in PICWTS. Note: The values undergo a square root, so if you want to enhance the power of something by 10, the number needs to be 100.
PICWTS= 1, 1, 1, 1, 1 WB, WL, WC, WS, WT
landmark position
In general, our focus in on the relative position of the landmarks to the image, but there are other factors:
- WB: body -- The solution controlled by the connection between images and the landmark.
- WO: overlaps -- The position is impacted by the overlapping landmarks
- WL: limbs -- The solution controlled by the limb data (for images that have limbs, the position of the landmarks gives a strong constraint on where the spacecraft can be).
- WR: reference. It will use the existing shape model as a reference. This ensures it doesn't deviation too far from the existing solution.
INIT_LITHOS.TXT contains the variable LMKWTS. Normally the value is one, meaning no extra weighting is use beyond the default values in SPC. However, if you want to increase (or decrease) the impact that one of these constrains have, you can increase (or decrease) the number in PICWTS. Note: The values undergo a square root, so if you want to enhance the power of something by 10, the number needs to be 100.
LMKWTS= 1, 0, 1, 0 WB, WO, WL, WR