B-spline surface points does not correspond to model u, v parameter

[TobyBorland]

Describe the bug
u,v, parametric values of a closed Bspline surface do not appear to correspond with the anticipated model geometry.
This happens on a B-spline-with-knots surface exported by the FreeCAD STEP geometry engine, while other surfaces behave as anticipated. This surface is closed along one side.

S.evalpts[0]
S..evaluate_single((0., 0.))
S.derivatives(0.0, 0.0, 0)
do not return the same point.

I may have misunderstood some aspect to this library, please comment and reassign as appropriate.

To Reproduce
`from geomdl import BSpline
from geomdl import evaluators
import numpy as np
from geomdl import compatibility
from geomdl import helpers

knotUvector = [0.0, 0.0, 0.0, 0.0, 0.5, 1.0, 1.0, 1.0, 1.0]
knotVvector = [1.408501368196, 1.570796326795, 1.570796326795, 1.570796326795, 2.356194490192, 2.356194490192,
2.856730419592, 2.856730419592, 2.981864401942, 2.981864401942, 3.106998384292, 3.106998384292,
3.169565375467, 3.169565375467, 3.232132366642, 3.232132366642, 3.357266348992, 3.357266348992,
3.525162636266, 3.525162636266, 3.793796695902, 3.793796695902, 4.223611191322, 4.223611191322,
4.911314383992, 4.911314383992, 5.39291028181, 5.39291028181, 5.874506179628, 5.874506179628,
6.046294058204, 6.046294058204, 6.218081936781, 6.218081936781, 6.261028906425, 6.261028906425,
6.303975876069, 6.303975876069, 6.389869815357, 6.389869815357, 6.561657693933, 6.561657693933,
6.796162586065, 6.796162586065, 7.140594928107, 7.140594928107, 7.691686675375, 7.691686675375,
7.853981633974, 7.853981633974, 7.853981633974, 8.639379797371]

#knotVvector = [kv - min(_knotVvector) for kv in _knotVvector]

controlPointsList = [[[5.00000000e-01, 4.89842542e-16, 1.94000000e+00], [0.5 , 0.34334628, 1.94],
[0.47970362, 0.69078459, 1.94], [0.39544685, 1.25001608, 1.94], [0.35363397, 1.46634455, 1.94],
[0.25173233, 1.73076161, 1.94], [0.22875243, 1.78300213, 1.94], [0.17014475, 1.88498053, 1.94],
[0.14147652, 1.93836645, 1.94], [0.03817818, 1.9990141 , 1.94], [-0.02525655, 2.00311907, 1.94],
[-0.09998333, 1.96538689, 1.94], [-0.12277512, 1.94064082, 1.94], [-0.18402992, 1.86740293, 1.94],
[-0.21140698, 1.81577046, 1.94], [-0.26822354, 1.69431319, 1.94], [-0.29350409, 1.62318021, 1.94],
[-0.35104497, 1.43583831, 1.94], [-0.37754281, 1.31929509, 1.94], [-0.43441625, 1.01719295, 1.94],
[-0.45762795, 0.8298337 , 1.94], [-0.4990324 , 0.34106292, 1.94], [-0.50564302, 0.03948469, 1.94],
[-0.48873301, -0.47279363, 1.94], [-0.4734661 , -0.68443663, 1.94], [-0.42093597, -1.10461872, 1.94],
[-0.38541925, -1.31292279, 1.94], [-0.30373212, -1.59271487, 1.94], [-0.2789671 , -1.66608308, 1.94],
[-0.21601647, -1.80952625, 1.94], [-0.18303939, -1.88172746, 1.94], [-0.098698 , -1.96187381, 1.94],
[-0.07931412, -1.97794075, 1.94], [-0.02281914, -2.00114215, 1.94], [ 0.01938063, -2.00183212, 1.94],
[ 0.10560777, -1.96848121, 1.94], [ 0.13224001, -1.93181438, 1.94], [ 0.20923139, -1.82931073, 1.94],
[ 0.24071689, -1.75812759, 1.94], [ 0.30781136, -1.58676168, 1.94], [ 0.33673456, -1.48501092, 1.94],
[ 0.39638483, -1.23617637, 1.94], [ 0.42187291, -1.08683116, 1.94], [ 0.4735693 , -0.69679181, 1.94],
[ 0.49067666, -0.4547692 , 1.94], [ 0.49905809, -0.14204254, 1.94], [ 0.5 , -0.0709492, 1.94 ],
[5.00000000e-01, 4.89842542e-16, 1.94000000e+00]],
[ [5.00000000e-01, 4.89842542e-16, 1.95570796e+00], [0.5 , 0.34318685, 1.95570796], [0.47966684, 0.69102865, 1.95570796],
[0.39547029, 1.24986054, 1.95570796], [0.35344318, 1.46683961, 1.95570796], [0.25178002, 1.73063785, 1.95570796],
[0.22861271, 1.78324524, 1.95570796], [0.17028446, 1.88473742, 1.95570796], [0.14012147, 1.93916201, 1.95570796],
[0.0388557 , 1.99861632, 1.95570796], [-0.02606528, 2.00271071, 1.95570796], [-0.0991746 , 1.96579525, 1.95570796],
[-0.1229573 , 1.940423 , 1.95570796], [-0.18366557, 1.86783855, 1.95570796], [-0.21148693, 1.81559954, 1.95570796],
[-0.26811626, 1.69454252, 1.95570796], [-0.29353978, 1.62306403, 1.95570796], [-0.35098788, 1.43602419, 1.95570796],
[-0.37756172, 1.31919464, 1.95570796], [-0.43438599, 1.01735367, 1.95570796], [-0.45763656, 0.82973205, 1.95570796],
[-0.49901862, 0.34122555, 1.95570796], [-0.50563829, 0.03934136, 1.95570796], [-0.48873633, -0.47269325, 1.95570796],
[-0.47344945, -0.68456984, 1.95570796], [-0.42095262, -1.10448551, 1.95570796], [-0.38532937, -1.31323062, 1.95570796],
[-0.30376417, -1.59260507, 1.95570796], [-0.27887457, -1.66629393, 1.95570796], [-0.216109 , -1.80931541, 1.95570796],
[-0.18221003, -1.88251557, 1.95570796], [-0.09890534, -1.96167678, 1.95570796], [-0.07863915, -1.97821795, 1.95570796],
[-0.02349411, -2.00086495, 1.95570796], [ 0.02008333, -2.00156033, 1.95570796], [ 0.10420237, -1.9690248 , 1.95570796],
[ 0.13243341, -1.9315569 , 1.95570796], [ 0.20884459, -1.8298257 , 1.95570796], [ 0.24078512, -1.75795331, 1.95570796],
[ 0.30771822, -1.58699958, 1.95570796], [ 0.336762 , -1.48489647, 1.95570796], [ 0.39634453, -1.23634447, 1.95570796],
[ 0.42188595, -1.08673276, 1.95570796], [ 0.47354843, -0.69694924, 1.95570796], [ 0.49067972, -0.45465521, 1.95570796],
[ 0.4990572 , -0.14207611, 1.95570796], [ 0.5 , -0.07091625, 1.95570796], [5.00000000e-01, 4.89842542e-16, 1.95570796e+00]],
[ [4.86998832e-01, 4.89046476e-16, 1.98699883e+00], [0.48699883, 0.342868 , 1.98699883], [0.46673723, 0.68957982, 1.98699883],
[0.38266109, 1.24761249, 1.98699883], [0.34093014, 1.46315448, 1.98699883], [0.23974395, 1.72571507, 1.98699883],
[0.21706105, 1.77725323, 1.98699883], [0.15929167, 1.87777298, 1.98699883], [0.13082889, 1.92954148, 1.98699883],
[0.03362825, 1.9866091 , 1.98699883], [-0.02182267, 1.9902884 , 1.98699883], [-0.09169706, 1.95500636, 1.98699883],
[-0.11334884, 1.9316463 , 1.98699883], [-0.17296406, 1.86036874, 1.98699883], [-0.19987048, 1.80974882, 1.98699883],
[-0.25612534, 1.68949231, 1.98699883], [-0.28118298, 1.61901445, 1.98699883], [-0.33844554, 1.43257872, 1.98699883],
[-0.36482281, 1.31658841, 1.98699883], [-0.42154875, 1.01526977, 1.98699883], [-0.44469901, 0.82843134, 1.98699883],
[-0.4860363 , 0.34045341, 1.98699883], [-0.49263473, 0.03948361, 1.98699883], [-0.47574886, -0.47206357, 1.98699883],
[-0.4605154 , -0.68322344, 1.98699883], [-0.40808518, -1.10260628, 1.98699883], [-0.37266948, -1.31020261, 1.98699883],
[-0.29134814, -1.5887418 , 1.98699883], [-0.26678432, -1.66149098, 1.98699883], [-0.20438887, -1.80366908, 1.98699883],
[-0.17159547, -1.87466718, 1.98699883], [-0.09036418, -1.95185812, 1.98699883], [-0.07235017, -1.96674586, 1.98699883],
[-0.01990501, -1.98828408, 1.98699883], [ 0.01679873, -1.98889098, 1.98699883], [ 0.09670157, -1.95798619, 1.98699883],
[ 0.1224248 , -1.92323386, 1.98699883], [ 0.19767559, -1.82304756, 1.98699883], [ 0.22881526, -1.75286481, 1.98699883],
[ 0.2954256 , -1.58273541, 1.98699883], [ 0.3241739 , -1.48163681, 1.98699883], [ 0.38362096, -1.23364992, 1.98699883],
[ 0.40902358, -1.08482771, 1.98699883], [ 0.46061824, -0.69555585, 1.98699883], [ 0.47768933, -0.45407891, 1.98699883],
[ 0.48605889, -0.14179493, 1.98699883], [ 0.48699883, -0.07085037, 1.98699883], [4.86998832e-01, 4.89046476e-16, 1.98699883e+00]],
[ [4.55707963e-01, 4.87130526e-16, 2.00000000e+00], [0.45570796, 0.34144534, 2. ], [0.43546743, 0.68709594, 2. ],
[0.35192856, 1.24156264, 2. ], [0.31002992, 1.45632001, 2. ], [0.2109719 , 1.71335835, 2. ],
[0.18868458, 1.76383105, 2. ], [0.13340877, 1.86001193, 2. ], [0.1028943 , 1.90965694, 2. ],
[0.0238317 , 1.95607551, 2. ], [-0.01493569, 1.95871229, 2. ], [-0.0703763 , 1.93071838, 2. ],
[-0.09097223, 1.90962753, 2. ], [-0.1457104 , 1.84418108, 2. ], [-0.17224094, 1.79496496, 2. ],
[-0.22682497, 1.67828019, 2. ], [-0.25158964, 1.60879053, 2. ], [-0.3080243 , 1.42505025, 2. ],
[-0.33424087, 1.30990294, 2. ], [-0.39052806, 1.01091489, 2. ], [-0.41359665, 0.82488302, 2. ],
[-0.45473415, 0.33926352, 2. ], [-0.46131868, 0.03923685, 2. ], [-0.4445046, -0.4701355, 2. ],
[-0.42931762, -0.68053046, 2. ], [-0.37718462, -1.09753587, 2. ], [-0.3418306, -1.3041801, 2. ],
[-0.26159733, -1.57899248, 2. ], [-0.23730552, -1.65079797, 2. ], [-0.17656149, -1.78921303, 2. ],
[-0.14263981, -1.85901713, 2. ], [-0.07065974, -1.927417 , 2. ], [-0.05443979, -1.94027447, 2. ],
[-0.01404107, -1.95686544, 2. ], [ 0.01178166, -1.95728162, 2. ], [ 0.0728724 , -1.93365296, 2. ],
[ 0.09913126, -1.90214387, 2. ], [ 0.16920455, -1.80885073, 2. ], [ 0.20028696, -1.73990163, 2. ],
[ 0.26545723, -1.57345033, 2. ], [ 0.29398994, -1.47332114, 2. ], [ 0.35283258, -1.22785565, 2. ],
[ 0.37812037, -1.07983828, 2. ], [ 0.42941245, -0.69284936, 2. ], [ 0.44643695, -0.45222337, 2. ],
[ 0.45477123, -0.14125616, 2. ], [ 0.45570796, -0.07055639, 2. ], [4.55707963e-01, 4.87130526e-16, 2.00000000e+00]],
[ [4.40000000e-01, 4.86168722e-16, 2.00000000e+00], [0.44 , 0.34077118, 2. ], [0.41977928, 0.68578778, 2. ],
[0.336495 , 1.23856467, 2. ], [0.29456594, 1.45276485, 2. ], [0.19651641, 1.70718636, 2. ],
[0.1744747 , 1.75703212, 2. ], [0.12038053, 1.85115693, 2. ], [0.08921129, 1.89947525, 2. ],
[0.01874379, 1.94084753, 2. ], [-0.01127545, 1.94296363, 2. ], [-0.0598763 , 1.91842336, 2. ],
[-0.07969348, 1.89862881, 2. ], [-0.13212057, 1.83594557, 2. ], [-0.15835089, 1.78758639, 2. ],
[-0.21214317, 1.67259416, 2. ], [-0.23672487, 1.6036873 , 2. ], [-0.29276722, 1.42122432, 2. ],
[-0.31888405, 1.30657205, 2. ], [-0.37496332, 1.0086884 , 2. ], [-0.39798116, 0.82312728, 2. ],
[-0.43902399, 0.33862537, 2. ], [-0.44559926, 0.03914896, 2. ], [-0.42881919, -0.4691928 , 2. ],
[-0.41366057, -0.67914515, 2. ], [-0.36166841, -1.09502398, 2. ], [-0.32637208, -1.30107955, 2. ],
[-0.24665442, -1.57412589, 2. ], [-0.22253043, -1.64537717, 2. ], [-0.16256897, -1.78200904, 2. ],
[-0.12831229, -1.85096302, 2. ], [-0.0607161 , -1.91519705, 2. ], [-0.04561823, -1.9269163 , 2. ],
[-0.01092797, -1.94116291, 2. ], [ 0.00908672, -1.941482 , 2. ], [ 0.06126296, -1.92130129, 2. ],
[ 0.0873894 , -1.89162136, 2. ], [ 0.15500922, -1.80159469, 2. ], [ 0.18594868, -1.73343788, 2. ],
[ 0.25043654, -1.56872952, 2. ], [ 0.27883076, -1.46917541, 2. ], [ 0.33738697, -1.22490475, 2. ],
[ 0.36260374, -1.07735828, 2. ], [ 0.41375243, -0.69145119, 2. ], [ 0.43074754, -0.4513205 , 2. ],
[ 0.4390651 , -0.14097727, 2. ], [ 0.44 , -0.07041708, 2. ], [4.40000000e-01, 4.86168722e-16, 2.00000000e+00]]]

BsplineKnotSurface = BSpline.Surface()
#BsplineKnotSurface = BSpline.Surface(normalize_kv=False)

BsplineKnotSurface.degree_u = 3
BsplineKnotSurface.degree_v = 3
BsplineKnotSurface.ctrlpts_size_u = len(controlPointsList)
BsplineKnotSurface.ctrlpts_size_v = len(controlPointsList[0])
BsplineKnotSurface.ctrlpts2d = controlPointsList
BsplineKnotSurface.knotvector_u = knotUvector
BsplineKnotSurface.knotvector_v = knotVvector
#BsplineKnotSurface.evaluator = evaluators.SurfaceEvaluator2()

Set evaluation delta

deltaFactor = 4
BsplineKnotSurface.delta_u = 1/(BsplineKnotSurface.ctrlpts_size_u * deltaFactor)
BsplineKnotSurface.delta_v = 1/(BsplineKnotSurface.ctrlpts_size_v * deltaFactor)

#BsplineKnotSurface.delta = 0.025

Evaluate surface points

BsplineKnotSurface.evaluate()

test_A = BsplineKnotSurface.evalpts[0]
test_B = BsplineKnotSurface.evaluate_single((0., 0.))
test_C = BsplineKnotSurface.derivatives(0.0, 0.0, 0)

if np.allclose(test_A, test_B) and np.allclose(test_A, test_C[0][0]) and np.allclose(test_B, test_C[0][0]):
print("PASS")
else:
print("FAIL")

pass`

Expected Behavior
It is anticipated that the surface point calculated from a (0.0, 0.0) u,v parametric description is at the corresponding zero corner of the model. While the point generated within evalpts[0] corresponds to this corner, a similar search using

Configuration:

• OS: Ubuntu 20.04
• Python distribution: [e.g. OS default, python.org, Anaconda]
• Python version: 3.8
• geomdl install source: GitHub PyCharm 2024
• geomdl version/branch: v5.3.1

Screenshots (Optional)
(Green dot is anticipated position, red dot is calculated zero-derivative position)

Additional Details (Optional)
Add any other context about the problem here.

[TobyBorland]

Seems the inline code has overflowed or I've used the wrong formatting, here's a link to the same code in my test repository.

https://github.com/TobyBorland/STEPaffine/blob/main/src/tests/UV_surface_issue.py

Another view,

[TobyBorland]

Surface and control points showing unusual behaviour of closed B-spline surface evalpoints,

[TobyBorland]

Present workaround is to generate a knotvector from supplied control points rather than using the knotvector generated within the FreeCAD OpenCASCADE kernel.

Evaluated evalpts surface point generation, evaluate() appears to use incomplete basis points set.