Claims

1. A method (30, 350) for localizing, in a space containing at least one determined object (91, 101, 111, 141), an object element (93, 143, X) associated to a particular 2D representation element (XL) in a determined 2D image of the space, the method comprising:

deriving (351) a range or interval of candidate spatial positions (95, 105, 114b, 115, 135, 145, 361') for the imaged object element (93, 143, X) on the basis of predefined positional relationships (381a', 381b');

restricting (35, 36, 352) the range or interval of candidate spatial positions to at least one restricted range or interval of admissible candidate spatial positions (93a, 93a', 103a, 112', 137, 147, 362'), wherein restricting includes at least one of:

limiting the range or interval of candidate spatial positions using at least one inclusive volume (96, 86, 106, 376, 426a, 426b) surrounding at least one determined object (91, 101); and

limiting the range or interval of candidate spatial positions using at least one exclusive volume (279, 299a-299e, 375) surrounding non-admissible candidate spatial positions; and

retrieving (37, 353), among the admissible candidate spatial positions of the restricted range or interval, a most appropriate candidate spatial position (363') on the basis of similarity metrics.

2. The method of claim 1, wherein in the space there are contained at least one first determined object (91) and one second determined object (101, 111),

wherein restricting (35, 36, 352) includes limiting the range or interval of candidate spatial positions (95, 115) to:

at least one first restricted range or interval of admissible candidate spatial positions (93a', 96a) associated to the first determined object (91); and

at least one second restricted range or interval of admissible candidate spatial positions (103a, 112') associated to the second determined object (101, 111),

wherein restricting (352) includes defining the at least one inclusive volume (96) as a first inclusive volume surrounding the first determined object (91) and/or a second inclusive volume (106) surrounding the second determined object (101), to limit the at least one first and/or second range or interval of candidate spatial positions to at least one first and/or second restricted range or interval of admissible candidate spatial positions; and

wherein retrieving (353) includes determining whether the particular 2D representation element (93) is associated to the first determined object (91) or is associated to the second determined object (101, 111).

3. The method of claim 2, wherein determining whether the particular 2D representation element (X_{L}) Is associated to the first determined object (91) or to the second determined object (101) is performed on the basis of similarity metrics.

4. The method of claim 2 or 3, wherein determining whether the particular 2D representation element is associated to the first determined object (91) or to the second determined object (101) is performed on the basis of the observation that:

one of the at least one first and second restricted range or interval of admissible candidate spatial positions is void; and

the other (93a) of the at least one first and second restricted range or interval of admissible candidate spatial positions is not void, so as to determine that the particular 2D representation element (93) is within the other (93a) of the at least one first and second restricted range of admissible candidate spatial positions.

5. The method of any of claims 2-4, wherein restricting (352) includes using information from a second camera (114) or 2D image for determining whether the particular 2D representation element (93) is associated to the first determined object (91) or to the second determined object (101, 111).

6. The method of claim 5, wherein the information from a second camera (114) or 2D image includes a previously obtained localization of an object element (93) contained in:

the at least one first restricted range or interval of admissible candidate spatial positions (96a), so as to conclude that the object element (93) is associated to the first object (91); or

the at least one second restricted range or interval of admissible candidate spatial positions (112'), so as to conclude that the object element (93) is associated to the second object (111).

7. A method (350, 450) comprising:

as a first operation (451), obtaining positional parameters associated to a second camera position (424b) and at least one inclusive volume (424a, 424b);

as a second operation (452), performing a method (350) according to any of the preceding claims for a particular 2D representation element for a first 2D image acquired at a first camera position, the method including:

analyzing (457a, 457b), on the basis of the positional parameters obtained at the first operation (451), whether both the following conditions are met:

(457b) at least one candidate spatial position (425d") would occlude at least one inclusive volume (426a) in a second 2D image obtained or obtainable at the second camera position, and

(457a) the at least one candidate spatial position (425d") would not be occluded (457a") by at least one inclusive volume (426a) in the second 2D image, so as, in case the two conditions are met (457a", 457b'):

to refrain (457b', 457c) from performing retrieving (353, 458) even If the at least one candidate spatial position (425d") was in the restricted range of admissible candidate spatial positions for the first 2D image and/or

to exclude (457b', 457c) the at least one candidate spatial position (425d") from the restricted range or interval of admissible candidate spatial positions for the first 2D image even if the at least one candidate spatial position (425d") was in the restricted range of admissible candidate spatial positions.

8. A method (350, 450) comprising:

as a first operation (451), obtaining positional parameters associated to a second camera position (424b) and at least one inclusive volume (424a, 424b);

as a second operation (452), performing a method (350) according to any of the preceding claims for a particular 2D representation element for a first 2D image acquired at a first camera position, the method including:

analyzing (457a), on the basis of the positional parameters obtained at the first operation (451), whether at least one admissible candidate spatial position (425e"') of the restricted range would be occluded by the at least one inclusive volume (426b) in a second 2D image obtained or obtainable at the second camera position, so as to maintain the admissible candidate spatial position (425e"') in the restricted range.

9. A method (430) including

as a first operation (431), localizing a plurality of 2D representation elements for a second 2D image,

as a second, subsequent operation (432), performing the deriving, the restricting and the retrieving of the method (350) according to any of the preceding claims for determining a most appropriate candidate spatial position for the determined 2D representation element ((x0, y0)) of a first determined 2D image, wherein the second 2D image and the first determined 2D Image are acquired at spatial positions in predetermined positional relationship,

wherein the second operation (432) further includes finding (435) a 2D representation element ((x',/)) in the second 2D image, previously processed in the first operation (431), which corresponds to a candidate spatial position (A') of the first determined 2D representation element ((x0, y0)) of the first determined 2D image,

so as to further restrict (436), in the second operation (432), the range or interval of admissible candidate spatial positions and/or to obtain similarity metrics on the first determined 2D representation element ((x0, y0)).

10. The method of claim 9, wherein the second operation (432) is such that, at the observation that the previously obtained localized position for the 2D representation element ((x',y')) in the second 2D image would be occluded to the second 2D image by the candidate spatial position (A') of the first determined 2D representation element ((x0, y0)) considered in the second operation:

further restricting (436) the restricted range or interval of admissible candidate spatial positions so as to exclude the candidate spatial position (A') for the determined 2D representation element ((x0, y0)) of the first determined 2D image from the restricted range or interval of admissible candidate spatial positions.

11. The method of claim 9 or 10, wherein, at the observation that the localized position (93) of the 2D representation element ((x',y')) ^{in} the second 2D image corresponds to the first determined 2D representation element ((x0, y0)):

restricting, for the determined 2D representation element ((x0, y0)) of the first determined 2D image, the range or interval of admissible candidate spatial positions so as to exclude, from the restricted range or interval of admissible candidate spatial positions (96a, 112'), positions more distant than the localized position (93).

12. The method of claim 9 or 10 or 11, further comprising, at the observation that the localized position (93) of the 2D representation element ((x',y')) in the second 2D image does not correspond to the localized position (112') of the first determined 2D representation element ((x0, y0)):

invalidating the most appropriate candidate spatial position (93) for the determined 2D representation element ((x0, y0)) of the first determined 2D Image as obtained in the second operation.

13. The method of any of claims 9-12, wherein the localized position (93) of the 2D

representation element ((x',y')) in the second 2D image corresponds to the first determined 2D representation element ((x0, y0)) when the distance of the localized position (93) is within a maximum predetermined tolerance distance to one of the candidate spatial positions of the first determined 2D representation element ((x0, y0)).

14. The method of any of claims 9-13, further comprising, when finding a 2D representation element ((x',y')) in the second 2D image, analysing a confidence or reliability value of the localization of the first a 2D representation element ((x',y')) in the second 2D image, and using it only in case of the confidence or reliability value being above a predetermined confidence threshold, or the unreliability value being below a predetermined threshold.

15. The method of claim 14, wherein the confidence value is at least partially based on the distance between the localized position and the camera position, and is increased for a closer distance.

16. The method of claim 15, wherein the confidence value is at least partially based on the number of objects (91, 111) or inclusive volumes (96) or restricted ranges of admissible spatial positions (96b), so as to increase the confidence value if, in the range or interval of admissible spatial candidate positions, there are found a fewer number of objects (91, 111) or inclusive volumes (96) or restricted ranges of admissible spatial positions (96b).

17. The method of any of the preceding claims, wherein restricting (352) includes defining at least one surface approximation (92, 132, 142), so as to limit the at least one range or interval of candidate spatial positions to at least one restricted range or interval of admissible candidate spatial positions.

18. The method of claim 17, wherein defining includes defining at least one surface

approximation (142) and one tolerance interval (147), so as to limit the at least one range or interval of candidate spatial positions to a restricted range or interval of candidate spatial positions defined by the tolerance interval, wherein the tolerance interval has:

a distal extremity (143"') defined by the at least one surface approximation; and a proximal extremity (147') defined on the basis of the tolerance interval; and retrieving, among the admissible candidate spatial positions of the restricted range or interval, a most appropriate candidate spatial position (143) on the basis of similarity metrics.

19. A method for localizing, in a space containing at least one determined object (141), an object element (143) associated to a particular 2D representation element in a 2D image of the space, the method comprising:

deriving a range or interval of candidate spatial positions (145) for the imaged object element (143) on the basis of predefined positional relationships;

restricting the range or interval of candidate spatial positions to at least one restricted range or interval of admissible candidate spatial positions (147), wherein restricting includes:

defining at least one surface approximation (142) and one tolerance interval (147), so as to limit the at least one range or interval of candidate spatial positions to a restricted range or interval of candidate spatial positions defined by the tolerance interval, wherein the tolerance interval has:

a distal extremity (143'") defined by the at least one surface approximation; and a proximal extremity (147') defined on the basis of the tolerance interval; and retrieving, among the admissible candidate spatial positions of the restricted range or interval, a most appropriate candidate spatial position (143) on the basis of similarity metrics.

20. The method of claim 18 or 19, reiterated by using an increased tolerance interval, so as to increase the probability of containing the object element (143).

21. The method of 18 or 19, reiterated by using a reduced tolerance interval, so as to reduce the probability of containing a different object element.

22. The method of any of claims 18-21, wherein restricting includes defining a tolerance value (to) for defining the tolerance interval (147).

23. The method of any of claims 18-22, wherein restricting includes defining a tolerance interval value Dd obtained from the at least one surface approximation (142) based on where r½ is the normal vector of the surface approximation (142) in the point (143'") where the interval of candidate spatial positions (145) intersects with the surface approximation (142), and vector a defines the optical axis of the determined camera or 2D image.

24. The method of claim 23, wherein at least part of the tolerance interval value Dd is defined from the at least one surface approximation (142) on the basis of

where t_{0} is a predetermined tolerance value, where i s the normal vector of the surface approximation (142) in the point (143"') where the interval of candidate spatial positions (145) intersects with the surface approximation (142), where vector d

defines the optical axis of the considered camera, and F_{max} clips the angle between T

and 5

25. The method of any of the claims 24, wherein retrieving includes:

considering a normal vector (

of the surface approximation (142) located at the intersection (143"') between the surface approximation (142) and the range or interval of candidate spatial positions (145);

retrieving, among the admissible candidate spatial positions of the restricted range or interval (149), a most appropriate candidate spatial position (143) on the basis of similarity metrics, wherein retrieving includes retrieving, among the admissible candidate spatial positions of the restricted range or interval (149) and on the basis of the normal vector a most appropriate

candidate spatial position on the basis of similarity metrics involving the normal vector

26. A method for localizing, in a space containing at least one determined object, an object element (143) associated to a particular 2D representation element in a determined 2D image of the space, the method comprising:

deriving a range or interval of candidate spatial positions (145) for the imaged object element (143) on the basis of predefined positional relationships;

restricting the range or interval of candidate spatial positions to at least one restricted range or interval of admissible candidate spatial positions (149), wherein restricting includes defining at least one surface approximation (142), so as to limit the at least one range or interval of candidate spatial positions (145) to a restricted range or interval of candidate spatial positions (149);

considering a normal vector

of the surface approximation (142) located at the intersection between the surface approximation (142) and the range or interval of candidate spatial positions (145);

retrieving, among the admissible candidate spatial positions of the restricted range or interval (149), a most appropriate candidate spatial position (143) on the basis of similarity metrics, wherein retrieving includes retrieving, among the admissible candidate spatial positions of the restricted range or interval (149) and on the basis of the normal vecto , a most appropriate

candidate spatial position on the basis of similarity metrics involving the normal vecto

27. The method of claim 25 or 26, wherein

retrieving comprises processing similarity metrics (c_{sum}) for at least one candidate spatial position (d) for the particular 2D representation element ((xO,gO),CL),

wherein processing involves further 2D representation elements ((x,y)) within a particular neighbourhood (N(cO,gO)) of the particular 2D representation element ((cq,gq)),

wherein processing includes obtaining a vecto n among a plurality of vectors within a predetermined range defined from vecto , to derive a candidate spatial position (D), associated to vector n, for each of the other 2D representation elements ((x,y)), under the assumption of a planar surface of the object in the object element, wherein the candidate spatial position (D) is used to determine the contribution of each of the 2D representation elements ((x,y)), in the neighbourhood (N(x0,y0)) to the similarity metrics (c_{Sum}).

28. The method of any of claims 25-27, wherein retrieving is based on a relationship of the type:

where (xo, yo) is the particular 2D representation element, (x, y) are elements in a neighbourhood of (xo, yo), K is the intrinsic camera matrix, d is a depth candidate representing the candidate spatial position,

is a function that computes a depth candidate for the particular 2D representation element (x,y) based on the depth candidate d for the particular 2D representation element (xo, yo) under the assumption of a planar surface of the object in the object element.

29. The method of claim 28, wherein retrieving is based on evaluating a similarity metric C_{sum}(d) of the type

where å_{(x},_{y)}Î N(x_{0},y_{0}) represents a sum or a general aggregation function.

30. The method of any of claims 25-29, wherein restricting includes obtaining a vector n normal to the at least one determined object (141) at the intersection (143) with the range or interval of candidate spatial positions (145) among a range or interval of admissible vectors within a maximum inclination angle relative to the normal vector

31. The method of any of claims 25-30, wherein restricting includes obtaining the vector normal to the at least one determined object (143) according to

where Q is the inclination angle around the normal vector q_{max} is a predefined maximum

inclination angle, F is the azimuth angle, and where

n is interpreted relative to an orthonormal coordinate system whose third axes (z) is parallel to and whose other two axes (x,y) are

orthogonal to

32. The method of any of claims 25-31, wherein the normal vecto ) is different for different

restricted ranges of admissible candidate spatial positions (96a, 112') associated to the same range of candidate spatial positions (115).

33. The method of any of claims 17-32, wherein restricting is only applied when the normal vector of the surface approximation (122a, 142) in the intersection (143"") between the surface

approximation (142) and the range or interval of candidate spatial positions (145) has a predetermined direction within a particular range of directions.

34. The method of claim 33, wherein the particular range of directions is computed based on the direction of the range or interval of candidate spatial positions (145) related to the determined 2D Image.

35. The method of claim 34, wherein restricting is only applied when the dot product between the normal vector of the surface approximation (122a, 142) in the intersection (143"") between

the surface approximation (142) and the range or interval of candidate spatial positions (145) and the vector describing the path of the candidate spatial positions from the camera has a predefined sign.

36. The method of any of claims 14-35, wherein restricting (352) includes defining at least one surface-approximation-defined extremity (93'") of at least one restricted range or interval of admissible candidate spatial positions (93a), wherein the at least one surface-approximation-defined extremity (93'") is located at the intersection between the surface approximation (92) and the range or interval of candidate spatial positions (95).

37. The method of claims 17-36, wherein the surface approximation (92) is selected by a user.

38. The method of any of claims 17-37, wherein restricting (352) includes sweeping along the range of candidate positions (135) from a proximal position towards a distal position (135) and is concluded at the observation that the at least one restricted range or interval of admissible candidate spatial positions (137) has a distal extremity (17) associated to a surface approximation (132).

39. The method of any of claims 17-38, wherein at least one inclusive volume (96, 136d, 206) is defined automatically from the at least one surface approximation (92, 132, 202).

40. The method of any of claims 17-39, wherein at least one inclusive volume (186) is defined from the at least one surface approximation (182) by scaling the at least one surface approximation (182).

41. The method of any of claims 17-40, wherein at least one inclusive volume (186) is defined from the at least one surface approximation (182) by scaling the at least one surface approximation from a scaling center (182a) of the at least one surface approximation (182).

42. The method of any of claims 17-41, wherein restricting involves at least one inclusive volume or surface approximation to be formed by a structure (200, 206) composed of vertices or control points, edges and surface elements, where each edge connects two vertices, and each surface element is surrounded by at least three edges, and from every vertex there exists a connected path of edges to any other vertex of the structure.

43. The method of claim 42, where each edge is connected to an even number of surface elements.

44. The method of claim 43, where each edge is connected to two surface elements.

45. The method of any of claim 42-44, wherein the structure (200, 206) occupies a closed volume which has no border.

46. The method of any of claims 17-45, wherein at least one inclusive volume (96, 206) is formed by a geometric structure (200), the method further comprising defining the at least one inclusive volume (96, 206) by:

shifting the elements (200a-200i) by exploding the elements (200a-200i) along their normals ; and

reconnecting the elements (200b, 200c) by generating additional elements (210bc, 210cb).

47. The method of claim 46, further comprising:

inserting at least one new control point (220) within the exploded area (200');

reconnecting the at least one new control point (220) with the exploded elements (210bc) to form further elements (220bc).

48. The method of any of claims 42-47, wherein the elements (200a-200b) are triangle elements.

49. The method of any of claims 17-48, wherein restricting (352) includes:

searching for restricted ranges or intervals (137) within the range or interval of candidate spatial positions (135) from a proximal position to a distal position, and ending the searching at the retrieval of a surface approximation.

50. The method of any of claims 17-49, wherein the at least one surface approximation (92, 132,

142) is contained within the at least one object (91, 141).

51. The method of any of claims 17-50, wherein the at least one surface approximation (92, 132, 142) is a rough approximation of the at least one object.

52. The method of any of claims 17-51, further comprising, at the observation that the range or interval of candidate spatial positions obtained during deriving does not intersect with any surface approximation, defining the restricted range or interval of admissible candidate spatial positions as the range or interval of candidate spatial positions obtained during deriving.

53. The method of any of the preceding claims, wherein the at least one inclusive volume is a rough approximation of the at least one object.

54. The method of any of the preceding claims, wherein retrieving is applied to a random subset among the restricted range or interval of admissible candidate positions and/or admissible normal vectors.

55. The method of any of the preceding claims, wherein restricting (352) includes defining at least one inclusive-volume-defined extremity (96"'; 10, II, 12, 13, 14, 15, 16) of the at least one restricted range or interval of admissible candidate spatial positions (137).

56. The method of any of the preceding claims, wherein the inclusive volume (96, 106) is defined by a user.

57. The method of any of the preceding claims, wherein retrieving (37, 353) includes determining whether the particular 2D representation element is associated to at least one determined object (91, 101) on the basis similarity metrics.

58. The method of any of the preceding claims, wherein at least one of the 2D representation elements is a pixel (XL) in the determined 2D image (22).

59. The method of any of the preceding claims, wherein the object element (93, 143) is a surficial element of the at least one determined object (91, 141).

60. The method of any of the preceding claims, wherein the range or interval of candidate spatial positions (95, 105, 114b, 115, 135, 145) for the imaged object element is developed in a depth direction with respect to the determined 2D representation element.

61. The method of any of the preceding claims, wherein the range or interval of candidate spatial positions for the imaged object element (93, 143) is developed along a ray (95, 105, 114b, 115, 135, 145) exiting from the nodal point of the camera with respect to the determined 2D representation element.

62. The method of any of the preceding claims, wherein retrieving (353) includes measuring similarity metrics along the admissible candidate spatial positions of the restricted range or interval (93a; 93, 103; 93a; 96a, 112'; 137) as obtained from a further 2D image (23) of the space and in predefined positional relationship with the determined 2D image (22).

63. The method of claim 62, wherein retrieving includes measuring similarity metrics along the 2D representation elements, in the further 2D image, forming an epi-polar line (21) associated to the at least one restricted range (45).

64. The method of any of the preceding claims, wherein restricting (35, 36, 352) includes finding an intersection (13-19, 13'-I9') between the range or interval of candidate positions (135, 295, 375) with at least one of the inclusive volume (136a-136f), exclusive volume (299a-299e, 379), and/or surface approximation (132, 172).

65. The method of any of the preceding claims, wherein restricting includes finding an extremity (13-19, 13'-I9') of a restricted range or interval of candidate positions (135, 295, 375) with at least one of the inclusive volume (136a-136f), exclusive volume (299a-299e, 379), and/or surface

approximation (132, 172).

66. The method of any of the preceding claims, wherein restricting includes:

searching for ranges or intervals (137) within the range or interval of candidate spatial positions (135) from a proximal position towards a distal position.

67. The method of any of the preceding claims, wherein defining (351) includes:

selecting a first 2D image (335) of the space and a second 2D image (335') of the space, wherein the first and second 2D images (335, 335') have been acquired at camera positions in a predefined positional relationship with each other;

displaying at least the first 2D image (335),

guiding a user to select a control point in the first 2D image (335), wherein the selected control point (330) is a control point (210) of an element (200a-200i) of a structure (200) forming a surface approximation or an exclusive volume or an inclusive volume;

guiding the user to selectively translate the selected control point (330), in the first 2D image (335), while limiting the movement of the control point (330) along the epi-polar line (331) associated to a second 2D-image-control-point (330') in the second 2D image (335'), wherein the second 2D-image-control-point (330') corresponds to the same control point (210, 330) of the element (200a-200i) in the first 2D image,

so as to define a movement of the element (2Q0a-200i) of the structure (200) in the 3D space.

68. The method of any of the preceding claims, wherein defining (351) includes:

selecting a first 2D image (345) of the space and a second 2D image (345') of the space, wherein the first and second 2D images have been acquired at camera positions in a predefined positional relationship with each other;

displaying at least the first 2D image (345),

guiding a user to select a control point (340) in the first 2D Image (345), wherein the selected control point is a control point (210) of an element (200a-200i) of a structure (200) forming a surface approximation or an exclusive volume or an inclusive volume;

obtaining from the user a selection associated to a new position (341) for the control point (340) in the first 2D image (345);

restricting the new position in the space of the control point (340) as a position on the epi-polar line (342), in the second 2D image (345'), associated to the new position (341) of the control point in the first 2D image (345), and determining the new position (34G) in the space as the position (341') on the epi-polar line (342) which is the closest to the initial position (340') in the second 2D image (345'),

wherein point (340') corresponds to the same control point (210, 340) of the element (200a-200i) of a structure (200) of the selected control point (340),

so as to define a movement of the element (200a-200i) of the structure (200).

69. A method for localizing, in a space containing at least one determined object, an object element associated to a particular 2D representation element in a determined 2D image of the space, the method comprising:

obtaining a spatial position for the imaged object element;

obtaining a reliability or unreliability value for this spatial position of the imaged object element;

in case of the reliability value does not comply with a predefined minimum reliability or the unreliability does not comply with a predefined maximum unreliability, performing the method of any of the preceding claims so as to refine the previously obtained spatial position.

70. A method for refining, in a space containing at least one determined object, a previously obtained localization of an object element associated to a particular 2D representation element in a determined 2D Image of the space, the method comprising:

graphically displaying the determined 2D image of the space;

guiding a user to define at least one inclusive volume and/or at least one surface

approximation and/or at least one surface approximation;

performing a method according to any of the preceding claims so as to refine the previously obtained localization.

71. The method of any of the preceding claims, further comprising, after the definition of at least one inclusive volume (376) or surface approximation, automatically defining an exclusive volume (379) between the at least one inclusive volume (376) or surface approximation and the position of at least one camera.

72. The method of any of the preceding claims, further comprising, at the definition of a first proximal inclusive volume (426b) or surface approximation and a second distal inclusive volume or surface approximation (422, 426a), automatically defining:

a first exclusive volume (C) between the first inclusive volume (426b) or surface

approximation and the position of at least one camera (424b);

at least one second exclusive volume (A, B) between the second inclusive volume (426a) or surface approximation (422) and the position of at least one camera (424b), with the exclusion of a non-excluded region (D) between the first exclusive volume (C) and the second exclusive volume (A,

B).

73. The method of any of the preceding claims, applied to a multi-camera system.

74. The method of any of the preceding claims, applied to a stereo-imaging system.

75. The method of any of the preceding claims, wherein retrieving comprises selecting, for each candidate spatial position of the range or interval, whether the candidate spatial position is to be part of the restricted range of admissible candidate spatial positions.

76. A system (360, 380) for localizing, in a space for containing at least one determined object (91, 101, 111, 141), an object element (93, 143) associated to a particular 2D representation element in a determined 2D image of the space, the system comprising:

a deriving block (361) for deriving a range or interval of candidate spatial positions (95, 105, 114b, 115, 135, 145) for the Imaged object element (93, 143) on the basis of predefined positional relationships;

a restricting block (35, 36, 352) for restricting the range or interval of candidate spatial positions to at least one restricted range or interval of admissible candidate spatial positions (93a, 93a', 103a, 112', 137, 147), wherein the restricting block is configured for:

limiting the range or interval of candidate spatial positions using at least one inclusive volume (96, 86, 106) surrounding at least one determined object; and/or

limiting the range or interval of candidate spatial positions using at least one exclusive volume (279, 299a-299e, 375) including non-admissible candidate spatial positions; and

a retrieving block (37, 353) for retrieving, among the admissible candidate spatial positions of the restricted range or interval, a most appropriate candidate spatial position on the basis of similarity metrics.

77. The system of claim 76, further comprising a first and a second cameras for acquiring 2D images in predefined positional relationships.

78. The system of claim 76 or 77, further comprising at least one movable camera for acquiring

2D images from different positions and in predefined positional relationships.

79. The system of any of claims 76-78, further comprising a constraint definer (364) for rendering or displaying at least one 2D image to obtain an input (384a) for defining at least one constraint.

80. The system of any of claims 76-79, further configured to perform a method according to any of claims 1-76.

81. A non-transitory storage unit including instructions which, when executed by a processor, cause the processor to perform a method according to any of claims 1-75.