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Return a tuple of locations of x and y spline knots
SYNOPSIS
print(mrcal.knots_for_splined_models('LENSMODEL_SPLINED_STEREOGRAPHIC_order=2_Nx=4_Ny=3_fov_x_deg=200'))
( array([-3.57526078, -1.19175359, 1.19175359, 3.57526078]),
array([-2.38350719, 0. , 2.38350719]))
Splined models are defined by the locations of their control points. These are
arranged in a grid, the size and density of which is set by the model
configuration. This function returns a tuple:
- the locations of the knots along the x axis
- the locations of the knots along the y axis
The values in these arrays correspond to whatever is used to index the splined
surface. In the case of LENSMODEL_SPLINED_STEREOGRAPHIC, these are the
normalized stereographic projection coordinates. These can be unprojected to
observation vectors at the knots:
ux,uy = mrcal.knots_for_splined_models('LENSMODEL_SPLINED_STEREOGRAPHIC_order=2_Nx=4_Ny=3_fov_x_deg=200')
u = np.ascontiguousarray(nps.mv(nps.cat(*np.meshgrid(ux,uy)), 0, -1))
v = mrcal.unproject_stereographic(u)
# v[index_y, index_x] is now an observation vector that will project to this
# knot
ARGUMENTS
- lensmodel: the "LENSMODEL_..." string we're querying. This function only makes
sense for "LENSMODEL_SPLINED_..." models
RETURNED VALUE
A tuple:
- An array of shape (Nx,) representing the knot locations along the x axis
- An array of shape (Ny,) representing the knot locations along the y axis
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