Abstract:
The invention provides a method of viewing an image. Light is projected from the image. The projected light is split into first and second bundles of light focusing over a first and a second focal region respectively. The light at the first focal region is detected at a first resolution. The light at the second focal region is detected at a second resolution different from the first resolution.

Description:
[0001]    This patent application is a continuation-in-part of U.S. patent application Ser. No. 09/175,157 filed Oct. 19, 1998 (pending) which is a continuation-in-part of U.S. patent application Ser. No. 09/137,660 filed Aug. 20, 1998 (pending) which is a continuation-in-part of U.S. patent application Ser. No. 08/872,525 filed Jun. 11, 1997 (pending) which claims priority from U.S. Provisional Patent Application Ser. No. 60/020,292 filed Jun. 24, 1996. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1). Field of the Invention  
           [0003]    This invention relates to a imaging arrangement of the kind capable of capturing light received from a scene, and to a method of capturing an image of a scene, in particular at different resolutions.  
           [0004]    2). Discussion of Related Art  
           [0005]    Panoramic imaging arrangements have become popular in recent years for purposes of viewing 360° surrounding panoramic scenes. Older generations of panoramic imaging arrangements generally consisted of revolving periscope-like constructions having relatively complex mechanisms for revolving them. More recently, stationary panoramic imaging arrangements have been developed. A stationary panoramic imaging arrangement generally has one or more lenses, each having a vertically extending axis of revolution, which are used to refract or reflect light received from a 360° surrounding panoramic scene. The lenses alter the direction of the light, whereafter the light passes through a series of lenses which are located vertically one above the other and which further manipulate the light by, for example, focusing the light or altering the intensity of the light.  
           [0006]    In an imaging arrangement of the above kind an image of a very large view can be captured on a digital imaging detector array. The digital imaging detector array typically has pixels which are located relative to one another so that the image is digitized to a required resolution suitable for viewing, but not to a resolution which may be excessively high for purposes of transmitting data of the image and for processing the data.  
           [0007]    Software may be used for isolating specific portions of the image and then enlarging the portions for better viewing. When such an area is enlarged, detail of the portion of the image which is visible is usually limited because of the resolution at which the image is digitized. In certain instances, it may therefore be required that light from a portion of an image be captured at a higher resolution.  
         SUMMARY OF THE NVENTION  
         [0008]    The invention provides a method of viewing an image. Light is projected from the image. The projected light is split into first and second bundles of light focusing over a first and a second focal region respectively. The light at the first focal region is detected at a first resolution. The light at the second focal region is detected at a second resolution different from the first resolution.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention is further described by way of examples with reference to the accompanying drawings wherein:  
         [0010]    [0010]FIG. 1 is a side view illustrating apparatus, according to an embodiment of the invention, for capturing in a panoramic scene;  
         [0011]    [0011]FIG. 2 is an enlarged view of first and second lens blocks forming part of the apparatus of FIG. 1;  
         [0012]    [0012]FIG. 3 is a side view of a panoramic imaging arrangement forming part of the apparatus for capturing the panoramic scene of FIG. 1, which is complemented by a system of lenses positioned to receive light from a second scene which is located above the panoramic scene;  
         [0013]    [0013]FIG. 4 is an enlarged view illustrating the positioning of a virtual image plane created by the first lens block, and a focal plane of the system of lenses;  
         [0014]    [0014]FIG. 5 is a view illustrating how of light is focused on a digital detector array forming part of the panoramic imaging arrangement;  
         [0015]    [0015]FIG. 6 is a cross-sectional side view of the panoramic imaging arrangement of FIG. 1 which is modified to include apparatus for capturing a high resolution image;  
         [0016]    [0016]FIG. 7 is a view illustrating how light is focused and an image is rotated over another digital detector array used in the embodiment of FIG. 6.  
         [0017]    [0017]FIG. 8A is a cross-sectional side view of a portion of the panoramic imaging arrangement which is modified so that a set of lenses thereof is mounted to a support frame in the form of an interchangeable module;  
         [0018]    [0018]FIG. 8B is a plan view illustrating how an image is focused on a digital imaging detector array of the panoramic imaging arrangement utilizing the set of lenses of FIG. 8A;  
         [0019]    [0019]FIG. 9A is a cross-sectional side view of an alternative module including an alternative set of lenses; and  
         [0020]    [0020]FIG. 9B is a plan view which illustrates how an image is formed on the digital imaging detector array when the alternative module of FIG. 9A is used.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]    [0021]FIG. 1 of the accompanying drawings illustrates apparatus  10 , according to an embodiment of the invention, for capturing a panoramic scene. The apparatus  10  includes a vertically extending support structure  12 , and a panoramic imaging arrangement  14  which is secured to an upper end  16  of the support structure  12 .  
         [0022]    The support structure  12  may be any device having an upper end  16  which is high enough for purposes of providing a viewpoint of a panoramic scene. The support structure  12  is typically part of a housing for the panoramic imaging arrangement  14  and may, for example, include a vertically extending post, a tripod stand, or part of building structure.  
         [0023]    The panoramic imaging arrangement  14  includes a first, upper lens block  18 , a second, lower lens block  20 , and apparatus  22 , positioned below the second lens block  20 , for manipulating light so as to correct certain aberrations of the light and to focus the light (hereinafter generally referred to as the “light manipulation apparatus  22 ”).  
         [0024]    [0024]FIG. 2 is an enlarged view of the first and second lens blocks  18  and  20 .  
         [0025]    The first lens block  18  includes a transparent component or refractive lens  24  which has a substantially spherical convex outer and lower surface  26 , and a substantially spherical concave inner and upper surface  28 . Center points of the convex outer surface  26  and the concave inner surface  28  of the transparent lens  24  substantially coincide with one another.  
         [0026]    The concave inner surface  28  is covered with a thin layer of reflective material  30 . After the reflective material  30  is deposited, a substantially spherical convex reflective surface  32  (sometimes generally referred to herein as a “convex reflective lens”) is provided against the transparent lens  24 . The transparent lens  24  so covers the convex reflective surface  32 , thereby providing a shield protecting the convex reflective surface  32  against environmental conditions which may otherwise cause damage to the convex reflective surface  32 .  
         [0027]    The convex outer surface  26  of the transparent lens  24  and the convex reflective surface  32  have a common, substantially vertical axis of revolution  34 .  
         [0028]    The second lens block  20  is made out of cylindrical, transparent material. An upper end  36  of the second lens block  20  has a substantially spherical concave surface which conforms with the convex outer surface  26  of the transparent lens  24 .  
         [0029]    The transparent lens  24  and the second lens block  20  are secured to one another by means of a transparent optical cement (not shown) which is located between the upper end  36  of the second lens block  20  and the convex outer surface  26  of the transparent lens  24 . Transparent optical cements of the above kind are known in the art.  
         [0030]    Referring again to FIG. 1, the light manipulation apparatus  22  includes a system of lenses  38 , a digital detector array  40 , and a digital image corrector  42 .  
         [0031]    The system of lenses  38  includes a first set of lenses  44 , a second set of lenses  46 , and a third set of lenses  48 . The lenses work together to correct aberrations of light. Generally speaking the first set of lenses  44  is designed and configured to reduce astigmatism, the second set of lenses  46  for doing color correction, and the third set lenses  48  for creating an image of suitable scale and for fine-tuning certain other system aberrations as will further be discussed herein. One skilled in the art of optics will appreciate that the respective sets of lenses  44 ,  46 , and  48  are of conventional kind although their collective effect may be unique in completing the present embodiment. Further details of such lenses may be found in a handbook on modern optics such as in “Modern Optical Engineering” by Warren J. Smith (McGraw Hill, Inc.; 1990).  
         [0032]    The panoramic imaging arrangement  14  is secured to the upper end  16  of the support structure  12  by mounting the second lens block  20  directly to the upper end  16  of the support structure  12 . No metal or other components are therefore secured to the first lens block  18 .  
         [0033]    In use, light is received laterally from a 360° panoramic scene surrounding the first lens block  18  (see FIG. 2). Light from the panoramic scene enters the convex outer surface  26  of the transparent lens  24  of the first lens block  18  for an unbroken and continuous included angle  52  located in a vertical plane. The included angle  52  is about 110° covering more than a hemisphere and extends from an angle  54  which is about 55° below the horizon to an angle  56  which about 45° above the horizon. (The included angle  52  is therefore at least 60° and preferably at least 90°, and the angles  54  and  56  below and above the horizon are each therefore at least 30° below and above the horizon.)  
         [0034]    It should be noted that the lens blocks  18  and  20  are mounted to the support structure  12  so that light from the panoramic scene is capable of passing over the upper end  16  of the support structure  12 , i.e., without the support structure obscuring light from the panoramic scene.  
         [0035]    Light from the panoramic scene is refracted slightly upwardly when entering the transparent lens  24 . The light then travels through the transparent lens  24  and is reflected downwardly from the convex reflective surface  32 . The light then passes downwardly through the transparent lens  24  and exits the transparent lens  24  downwardly through the convex outer surface  26 .  
         [0036]    The light then passes through the transparent optical cement located between the first and second lens blocks  18  and  20 , whereafter the light enters the second lens block  20  through the upper end  36  thereof. The second lens block  20  has a diameter which is sufficiently large so that light from the entire included angle  52 , after being reflected by the convex reflective surface.  32 , enters the second lens block  20  through its upper end  36 . The light then travels through the second lens block  20  and exits the second lens block through a lower end  60  thereof. Although not shown in particular detail in the figures, the cylindrical outer surface of the second lens block  20  is typically covered to prevent light from entering into the second lens block  20  in a sideways direction. This may be accomplished with the upper end  16  of the support structure shown in FIG. 2.  
         [0037]    Should an attempt be made to focus the light after leaving the second lens block  20 , certain aberrations would be noticed. These aberrations include astigmatism, abnormality in color, lack of image plane flatness, and a value of f-theta which is less than 1. The value f-theta is indicative of how much compression of view occurs in a vertical direction of an image view, resulting in more vertical compression in one area of the image view than in another area of the image view. Values of f-theta are expressed as fractions of 1 so that a value of f-theta approaching 1 would be indicative of more uniform compression, and a value of f-theta which is a smaller fraction of 1 would be indicative of more non-uniform compression.  
         [0038]    A number of factors, alone and in combination, contribute to these aberrations, including the relatively large size of the included angle  52 , the relatively low inclination of the angle  54  below the horizon, the relatively high inclination of the angle  56  above the horizon, and the particular choice of lenses, including the choice of a substantially spherical convex outer surface  26  of the transparent lens  24 , and the substantially spherical convex reflective surface  32 . These aberrations occur even though a reflective surface  32  is used which causes less aberrations in color than a refractive surface would and even though the transparent lens  24  has a convex outer surface  26  which assist greatly in reducing aberrations.  
         [0039]    The light manipulation apparatus  22  (see FIG. 1), however, functions to correct or at least to reduce these aberrations.  
         [0040]    In particular, the first set of lenses  44  is positioned so that light from the second lens block  20  passes through the first set of lenses  44 . The first set of lenses  44  then generally corrects or at least reduces astigmatism of the light to an acceptable level.  
         [0041]    The second set of lenses  46  is positioned to receive the light, after passing through the first set of lenses  44 , and generally functions so as to do color correction of the light.  
         [0042]    The third set of lenses  48  is positioned to receive light, after passing through the second set of lenses  46 , and generally functions to reduce the effect of compression so that the value f-theta is adjusted closer to 1, typically to a value above 0.5. The third set of lenses  48  also functions to flatten the image plane and focus the image on the digital detector array  40 .  
         [0043]    Certain aberrations may still exist, even after the light passes through the system of lenses  38 . For example, the value of f-theta, although adjusted to be closer to 1, may still be somewhat below 1.  
         [0044]    The digital image corrector  42  is coupled to the digital detector array  40  so as to receive the image captured by the digital detector array  40 . The digital image corrector  42  is capable of adjusting the image so as to correct for certain, still existing aberrations. For example, the digital image corrector  42  may adjust f-theta so as to be closer or substantially equal to 1. One skilled in the art would appreciate that the digital image corrector  42  typically has a processor and memory with an executable program which corrects the aberrations in the light referred to.  
         [0045]    As mentioned previously, one unique feature is that a substantially spherical convex reflective surface  32  is used which is protected from environmental conditions which may otherwise result in damage to the reflective surface  32 . Reflective lenses generally have the advantage that they reflect light with little or no aberrations in color of the reflected light and convex reflective lenses have the added advantage that they require less power than, for example, concave reflective lenses.  
         [0046]    It should also be evident from the aforegoing description that another advantage is that the panoramic imaging arrangement  14  can be mounted to the support structure  12  in a manner wherein the support structure  12  does not obscure light from a panoramic view from reaching the first lens block  18 .  
         [0047]    A further advantage of the invention is that lenses having substantially spherical surfaces are used. Spherical surfaces are easier to manufacture than paraboloidal, hyperboloidal, ellipsoidal or other aspheric surfaces and are therefore less expensive to manufacture.  
         [0048]    Yet a further advantage is that a relatively large included angle  52  can be received which extends from a relatively large angle  54  below the horizon to a relatively large angle  56  above the horizon.  
         [0049]    Although spherical surfaces are used, at least one of which having a reflective surface, and regardless of the choice of angles  52 ,  54 , and  56 , a final image is created which is corrected for astigmatism and color, which is flattened, and in which the value of f-theta is controlled.  
         [0050]    It can be seen from FIG. 1 that the upper lens block  18  is capable of receiving light directly from a surrounding panoramic scene up to an angle  56  which is about 45° above the horizon. The upper lens block  18  therefore has a “blind spot” of about 90° located above the angle  56 . The first lens block  18  is therefore capable of receiving light from the first, 360° surrounding panoramic scene but is unable to receive light from a second scene, perhaps the sky, which is located above the panoramic scene. FIG. 3 is a sectioned side view of the panoramic imaging arrangement  14  wherein the upper lens block  18  is complemented by a system of lenses  66 ,  68 ,  70  and  72  located above the upper lens block  18 , each having a vertical axis of revolution which substantially coincides with the axis of revolution  34  of the convex outer surface  26  and the convex reflective surface  32 .  
         [0051]    The lens  66  is located above the lenses  68 ,  70  and  72  and is positioned to receive light directly from the second scene which is located above the panoramic scene. The lens  66  receives light from the second scene for an unbroken included angle  74 , located in a plane of the axis of the revolution  34 , of about 90° extending from an angle  76  which is located about 45° below vertical, over vertical, to an angle  78  on an opposing side of about 45° below vertical. The lens  66  therefore receives light from the blind spot of the upper lens block  18 . The total included angle of light received by the first lens block  18  and the lens  66  is therefore 310° (twice in the unbroken included angle  52  of about 110° plus the unbroken included angle  54  of about 90°).  
         [0052]    After passing through and being refracted by the lens  66 , the light from the second scene then passes through and is refracted by the lenses  68 ,  70  and  72 . The lenses  66 ,  68 ,  70  and  72  may be shown in conceptual detail only. One of ordinary skill in the art would however appreciate that the configuration of the lenses  66 ,  68 ,  70  and  72  may be of conventional kind and may be similar to a conventional wide angle lens arrangement.  
         [0053]    [0053]FIG. 4 is an enlarged view illustrating in particular an area between the reflective surface  32  and the system of lenses  66 ,  68 ,  70  and  72 . From a perspective below the reflective surface  32 , a virtual image of the surrounding panoramic scene may be perceived in a planar zone  80  which is located between the reflective surface  32  and the system of lenses  66 ,  68 ,  70 , and  72 . When light reflected by the reflective surface  32  is then further manipulated as hereinbefore described, it would be the same as if light directly from the virtual image is further manipulated.  
         [0054]    The system of lenses  66 ,  68 ,  70  and  72  is configured so as to project and focus light from the second scene on a virtual planar zone  82  which coincides with, or is located within the planar zone  80  of the virtual image. Although the zone  82  is shown as being flat, it should be understood that it may be curved, perhaps to conform with the zone  80  of the virtual image of the surrounding panoramic scene. The light from the second scene is then further refracted and further manipulated together with and in a similar manner to light reflected from the reflective surface  32 , thus facilitating eventual focusing of light from both the first, surrounding panoramic scene and from the second scene.  
         [0055]    Referring again to FIG. 3, an opening  84  is formed in the reflective material  30 , forming the reflective surface  32 , through which light, after leaving the lens  72 , may pass into the transparent lens  24 . The light from the second scene then passes through the transparent lens  24  and the second lens block  20  and exits the second lens block  20  through the lower surface  60  thereof.  
         [0056]    The light from the second scene then passes through the respective sets of lenses  44 , 46 , and  48  together with light from the first, surrounding panoramic scene. Light requiring more correction for astigmatism or other aberrations generally passes through edge regions of the sets of lenses  44 , 46  and  48  and light requiring less correction generally passes through central regions of the sets of lenses  44 ,  46  and  48 . For example, light from the angle  56  above the horizon requires more correction after being reflected from the reflective surface  32  than light from the angle  54  below the horizon, and accordingly passes through the sets of lenses  44 ,  46  and  48  further towards the edges thereof than light from the angle  54  below the horizon. Light coming from the system of lenses  66 ,  68 ,  70  and  72  may also require less correction than light reflected from the reflective surface  32 , and accordingly passes through central regions of the sets of all lenses  44 ,  46  and  48  with correspondingly less correction of aberrations. Light from the second scene is then focused on the image capturing apparatus  40  together with light from the first, surrounding panoramic scene.  
         [0057]    [0057]FIG. 5 illustrates the manner in which light from the first, surrounding panoramic scene and the second scene are focused on the digital detector array  40 . Light from the first, surrounding panoramic scene focuses on an outer ring  86  with an inner edge of the ring  86  corresponding to the angle  54  located about 55° below the horizon and an outer edge of the ring  84  corresponding to the angle  56  located about 45° above the horizon. Light from the second scene focuses on a circle  88  located within the ring  86  with an outer edge of the circle  88  corresponding to the angles  76  and  78  located about 45° below vertical and a center of the circle corresponding to vertical.  
         [0058]    [0058]FIG. 6 now illustrates one modification of the panoramic imaging arrangement  10  of FIG. 1 which, in addition, includes apparatus  110  for capturing a high resolution image of the panoramic scene. The apparatus  110  includes a half silvered mirror  112 , an electric motor  114 , a Pechan prism  116  and, in addition to the first digital imaging detector array  40 , also a second digital imaging detector array  118 .  
         [0059]    The electric motor  114  is mounted to the support structure  12  and the Pechan prism  116  is rotatably mounted to the support structure  12 . The electric motor  114  is connected to an external control  120  which is capable of operating the electric motor  114  so that the electric motor  114  rotates the Pechan prism  116 .  
         [0060]    The half silvered mirror  112  is located at about 45° relative to horizontal in a position between the third set of lenses  48  and the first digital imaging detector array  40 . The half silvered mirror  112  is partially transmissive so that the light, after leaving the first set of lenses  48  is split into a first bundle of light  122  and a second bundle of light  124 . The first bundle of light is a portion of the light which is transmitted through the half silvered mirror  112  and the second bundle of light is a portion of the light which is reflected by the half silvered mirror  112  in substantially a horizontal direction towards the Pechan prism  116 .  
         [0061]    The first bundle of light  122  focuses on the first digital imaging detector array  40  as hereinbefore described with reference to FIG. 1. The first digital imaging detector array  40  is large enough to capture the entire image focused thereon of the 360° surrounding panoramic scene for the entire included angle  52 , and is connected to an output  128  so that data of the image focused thereon can be provided to the output  128 . The output  128  typically includes a screen on which the entire panoramic scene, or at least a substantial portion thereof can be viewed. Because such a large area of the panoramic scene is viewed, it is not necessary to view smaller portions of the panoramic scene at high resolution. The first digital imaging detector array  40  therefore typically has a resolution of about 1,000 pixels on an X axis thereof and 1,000 pixels on a Y axis thereof, which is sufficient for purposes of viewing the entire panoramic scene at a reasonable resolution. The resolution of the first digital imaging detector array is however not so high as to substantially burden data transmission and processing of data of the image created thereon.  
         [0062]    The second bundle of light  124  passes through the Pechan prism  116  and focuses in a focal region  126  in a plane of the second digital imaging detector array  118 .  
         [0063]    The second digital imaging detector array  118  has a much higher resolution than the first digital imaging detector array  40 , typically about 2,000 pixels on an X axis thereof and 2,000 pixels on a Y axis thereof, and is used for viewing isolated areas of the 360° surrounding panoramic scene at high resolution. The second digital imaging detector array  118  is also connected to the output  128  so that the isolated regions of the 360° surrounding panoramic scene can be viewed on the screen thereof. The first digital imaging detector array  40  thus has an array of detectors positioned relative to one another to detect the image of the 360° surrounding panoramic scene at a first resolution, and the second digital imaging detector array  118  as an array of detectors positioned relative to one another to detect only a portion of the 360° surrounding panoramic scene at a second resolution which is higher than the first resolution.  
         [0064]    The focal region  126  of the second bundle of light  124  is larger than the second digital imaging detector array. By operating the external control  120 , the electric motor  114  can rotate the Pechan prism  116  about an axis  129  extending in the direction of travel of the second bundle of light  124 . Rotation of the Pechan prism  116  causes rotation of the image created at the focal region  126 .  
         [0065]    [0065]FIG. 7 illustrates the positioning of the image  130  created at the focal region  126 , and the positioning of the second digital imaging detector array  118 . As with the image created on the first digital imaging detector array  40 , the image  130  is also in the shape of a ring. Rotation of the Pechan prism  116  causes rotation of the image  130  about a center point thereof and angular displacement of the second bundle of light  124  about the axis  128  by an angle which is twice the angle of rotation of the Pechan prism  116 . A portion of the 360° surrounding panoramic scene which is to be viewed at high resolution can, by rotating the image  130 , be selectively positioned over the second digital imaging detector array  118 . The digital imaging detector array  118  may then detect the required portion of the 360° surrounding panoramic scene at high resolution and provide data of the image to the output  128 .  
         [0066]    [0066]FIG. 8A illustrates another modification of the panoramic imaging arrangement of FIG. 1 or FIG. 6 which allows for capturing of an image of the 360° surrounding panoramic scene at a higher resolution. FIG. 8A illustrates a portion of the panoramic imaging arrangement, including a portion of the support structure  12 , and a module  150  which includes a support frame  152  and the third set of lenses  48 .  
         [0067]    The third set of lenses  48  is permanently mounted to the support frame  152 . The support frame  152  is subsequently releasably mounted to the support structure  12 . As previously mentioned, the support structure is typically part of a housing for the panoramic imaging arrangement. The support frame  152  may be located within the housing and be releasably attached thereto or may be in the form of an extension of the housing.  
         [0068]    As illustrated in FIG. 8B and previously described with reference to FIG. 5, an image is formed on the digital imaging detector array  40  which is in the form of a ring which includes light from 55° below the horizon to 45° above the horizon. An image so created may be advantageous when it is required to capture an image of a scene which includes a large included angle in a vertical plane.  
         [0069]    In other instances it may be required to view a smaller included angle at a higher resolution. FIG. 9A illustrates an alternative module  150 A which can be interchanged with the module  150  of FIG. 8A. The module  150 A includes a support frame  152 A which is identical to the support frame  152  of FIG. 8A, and an alternative third set of lenses  48 A mounted to the support frame  152 A. When the support frame  152 A is mounted to the support structure  12 , the alternative third set of lenses  48 A is located in a position wherein the alternative third set of lenses  48 A receives a portion of the light passing through the series of lenses including the upper lens block  12 , the lower lens block  20 , the first set of lenses  44 , and the second set of lenses  46 . The alternative third set of lenses  48 A is configured so that light leaving the alternative third set of lenses  48 A includes light only from an included angle which is smaller than and located within the included angle  52  of FIG. 1.  
         [0070]    For example, FIG. 9B illustrates that the alternative third set of lenses  48 A forms an image on the digital imaging detector array  40  in the form of a ring which includes light only from an included angle extending from 35° below the horizon to 35° above the horizon. An image of a smaller portion of the scene is thus formed on the digital imaging detector array  40 . The ring of FIG. 9B is substantially the same size as the ring of FIG. 8B so that, although the image captured in FIG. 9B is captured at the same resolution as the image captured in FIG. 8B, a smaller portion of the image is captured in FIG. 9B over the same area as in FIG. 8B. The portion of the image captured in FIG. 9B is thus captured at a higher resolution than the same portion of the image captured in FIG. 8B.  
         [0071]    In the same manner, another module may be used which, for example, ensures that only light is captured from an included angle extending from 45° below the horizon to 45° above the horizon, or from 40° below the horizon to 40° above the horizon, depending on requirement.  
         [0072]    While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described, since modifications may occur to those ordinarily skilled in the art.