Abstract:
A measuring system includes an optical site reference, such as a reference line within a scope used in surveying, and a calibrated reference scale which provides measurements by optical comparison to the optical site reference. The calibrated reference scale includes centimeter sections which in turn include upper and lower stepped sections. The upper and lower stepped sections are symmetrical with respect to one another such that the upper and lower stepped sections can be easily distinguished from one another from significant distance. Each of the steps of each stepped section indicates a specific, corresponding offset within the stepped section. The symmetry of the upper and lower stepped sections is in the relative positions of the long and short reference members. The calibrated reference scale includes a number of digit reference sections which are spaced a predetermined distance from a reference point along the calibrated reference scale and include an alphanumeric representation of that predetermined distance. The alphanumeric representation has a predetermined height such that the alphanumeric representation itself provides a reference for offsets from a base of the alphanumeric representation. In particular, those alphanumeric representations which have horizontal components place those horizontal components so as to provide relatively evenly spaced references which the digit reference section.

Description:
FIELD OF THE INVENTION 
     The present invention relates to measurement systems and, in particular, to a particularly effective calibration system for measuring with greater precision when optical comparison to a calibration is used for measuring. 
     BACKGROUND OF THE INVENTION 
     Surveying is as old as the art of civil engineering itself and predates even recorded history. One of the primary objectives of surveying is accuracy and precision in measurements made. In measuring an elevation, for example, a calibrated reference is placed at a point of interest while a scope is placed at a second point of reference. The second point of reference, and thus the scope, has a known elevation. The scope is leveled and aimed at the calibrated reference. A horizontal reference line is positioned within the view through the scope such that visual comparison of the reference line as viewed through the scope to the calibrated reference provides a measurement of the difference in elevation between the first and second points of interest. 
     At times, the distance between the first and second points of reference is considerable and accurate optical comparison between the reference line and the calibrated reference is difficult. For example, conventional calibration systems mark centimeters and perhaps half centimeters such that millimeters are merely estimated by a surveyor. Despite high quality optical magnification within the scope, comparison of the reference line within the scope to marked half-centimeters to estimate a measurement to the nearest millimeter is quite difficult. However, simply marking the calibrated reference with reference marks spaced by one millimeter is ineffective. Specifically, reference marks so close to one another appear as a single, indistinguishable mark from a distance notwithstanding high quality optical magnification. 
     Another problem with current surveying calibration references is that the view of the scope frequent has insufficient information to make a complete assessment of a current measurement. For example, it is common that only half-centimeter marks of the calibrated reference are visible through the scope at a particular measurement. Such generally requires that the scope be panned up and/or down to view markings which indicate absolute measurements such that the relation between the originally viewed half-centimeter marks and the absolute measurement markings can be determined. Only then can a measurement be made by comparison of the reference line to the half-centimeter marks which would otherwise lack context. 
     What is needed is a calibration system by which more precise and accurate measurements can be made and by which such measurements can be made without reference to distant portions of a calibrated reference. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a measuring system includes an optical site reference, such as a reference line within a scope used in surveying, and a calibrated reference scale which provides measurements by optical comparison to the optical site reference. The calibrated reference scale includes centimeter sections which in turn include upper and lower stepped sections. The upper and lower stepped sections are symmetrical with respect to one another such that the upper and lower stepped sections can be easily distinguished from one another from significant distance. Each of the steps of each stepped section indicates a specific, corresponding offset within the stepped section. In particular, each stepped section includes a long reference section which is adjacent to a short reference section along an adjacent edge of the long reference member. The short reference member is substantially less wide than the long reference member so as to expose a significant portion of the adjacent side. Thus, the exposed portion of the adjacent edge of the long reference member easily visible from significant distances and alignment of the optical site reference with the exposed portion of the adjacent edge can be easily recognized. The symmetry of the upper and lower stepped sections is in the relative positions of the long and short reference members. For example, the long reference member is above the short reference member in the upper stepped section and the long reference member is below the short reference member in the lower stepped section. 
     The long and short reference members have uniform heights such that edges of the long and short reference members opposite the adjacent edge, as well as the adjacent edge itself, provide references for predetermined offsets within the calibrated reference scale. Some of the advantages of the upper and lower stepped sections are best appreciated in the context of an illustrative example. Consider the lower stepped section in which (i) the bottom, non-adjacent edge of the long reference member is spaced two millimeters from a reference point on the calibrated reference scale, (ii) the height of the long reference member is one millimeter such that the top, adjacent edge of the long reference member is spaced three millimeters from the reference point, and (iii) the height of the short reference member is also one millimeter such that the top, non-adjacent edge of the short reference member is spaced four millimeters from the reference point. In this illustrative example, the top and bottom edges of the long reference member provide two- and three-millimeter references, respectively, relative to the reference point, and the top edge of the short reference member provides a four-millimeter reference relative to the reference point. As a result, references are provided with a precision of one-millimeter. To accomplish references separated by one-millimeter using simple tick marks would either result in marks which are too thin to see from significant distances notwithstanding high-quality optics or in marks which are too close together to distinguish from significant distances. Even if the marks are visible and distinct, determining with which mark the optical siting reference is aligned is difficult since the marks would look similar. Thus, the stepped sections provide references which are close to one another yet are easily recognizable and distinguished, even from significant distance. 
     Further in accordance with the present invention, the calibrated reference scale includes a number of digit reference sections. A digit reference section is spaced a predetermined distance from a reference point along the calibrated reference scale and includes an alphanumeric representation of that predetermined distance. The alphanumeric representation has a predetermined height such that the alphanumeric representation itself provides a reference for offsets from a base of the alphanumeric representation. In particular, those alphanumeric representations which have horizontal components place those horizontal components so as to provide relatively evenly spaced references which the digit reference section. Such horizontal components have a uniform, predetermined height and are spaced from one another by the same uniform, predetermined height. The following example is illustrative. 
     A digit reference section whose base is eight centimeters from a reference point along the calibrated reference scale includes an alphanumeric representation of the numeral eight. The digit reference section is one centimeter in height, and the alphanumeric representation is approximately one centimeter in height so as to provide a representation of the entire height of the digit reference section. The alphanumeric representation has top, middle, and bottom horizontal members which define two spaces therebetween, namely, an upper space between the top and middle horizontal members and a lower space between the middle and bottom horizontal members. Each of the horizontal members and the spaces between has a height of two millimeters. Thus, the tops and bottoms of each of the horizontal members and spaces between provides a reference corresponding to an offset within the digit reference section of an even number of millimeters. Similarly, the middles of each of the horizontal members and spaces between provides a reference corresponding to an offset within the digit reference section of an odd number of millimeters. 
     Thus, in accordance with the present invention, measurements can be determined from significant distances with greater accuracy and precision than can be achieved with conventional measuring systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustration of a calibration system in accordance with the present invention. 
     FIG. 2 is a block diagram of a component of the calibration system of FIG.  1 . 
     FIG. 3 is a block diagram of an alternative to the component of FIG.  2 . 
     FIG. 4 is a diagram of an alphanumeric representation of a digit centimeter section of the calibration system of FIG.  1 . 
     FIG. 5 is an illustration of a measuring system in accordance with the present invention which includes the calibration system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     In accordance with the present invention, a measuring system includes a calibration system  10  (FIG. 1) which includes digit reference sections which provide simultaneous context information and references for precise offsets within such digit reference section and includes symmetrical upper and lower stepped sections which provide easily recognizable references to very precise offsets within the stepped sections. 
     FIG. 1 shows a calibration system  10  in accordance with the present invention. Calibration system  10  is mounted on a surface of a flat, rigid, straight object  202  (FIG. 5) such as a pole which is placed in a position of interest  204  in generally the manner described above. In this illustrative example, position of interest  204  has an unknown elevation. In addition, a scope  206  is placed in a second position of interest  208 , which has a known elevation in this illustrative example, and is aimed at object  202  calibrated with calibration system  10  such that optical comparison of a reference line  210  within scope  206  to calibration system  10  as positioned on the object. Reference line  210  appears as a horizontal line superimposed upon calibration system  10  as shown in FIG.  5 . Optical comparison of reference line  210  with calibration system  10  can be performed by a human surveyor or, alternatively, by an electronic optical recognition systems such as those currently used in robotics. 
     Calibration system  10  (FIG. 1) includes a number of segmented decimeter portions, such as decimeter portion  12 . Decimeter portion  12  includes a numerical representation  14  of an absolute measurement For example, numerical representation  14  indicates an absolute measurement of 0.8 meters. 
     Decimeter portion  12  also includes ten centimeter portions, e.g., centimeter portions  16  and  18 . Each centimeter portion is divided into half-centimeter portions. 
     In addition to centimeter portions such as centimeter portions  16  and  18 , decimeter portion  12  includes digit centimeter portions, e.g., digit centimeter portions  20  and  22 , each of which identifies a specific numerical digit between zero and nine. Digit centimeter portions such as digit centimeter portion  20  simultaneously represent a relative measurement in the form of a number of centimeters offset from an edge of decimeter portion  12  and provide a measurement reference. The measurement reference is provided in the form of the height of the represented digit. For example, digit centimeter portion  20  represents the numerical digit, zero, and has a height of one centimeter. Accordingly, if reference line  210  (FIG. 5) within the scope is aligned with the top of digit centimeter portion  20 , the measurement is observed as 0.81 meters with 0.8 meters being observed from numerical representation  14  (FIG. 1) and 0.01 meters being observed from the height of digit centimeter portion  20 . Since each of the digit centimeter portions represents a numerical digit corresponding to a represented distance relative to the bottom of decimeter portion  12 , counting of decimeter portions, e.g., from the top or bottom of decimeter portion  12 , is obviated. 
     Furthermore, components of each of the digit centimeter portions are dimensioned to provide more detailed measuring information. Digit centimeter portion  26 , which represents the number eight and which represents eight centimeters offset from the bottom of decimeter portion  12 , is representative. Digit centimeter portion  26  is shown in isolation in FIG.  4  and includes a top bar  102 , a middle bar  104 , and a bottom bar  106 . Top bar  102  and middle bar  104  define an upper space  108  therebetween. Similarly, middle bar  104  and bottom bar  106  define a lower space  110  therebetween. To further aid in making a precise and accurate measurement, bars  102 - 106  and spaces  108 - 110  have a uniform width  122  which is equal to one-fifth of the total height of digit centimeter portion  26 . Since digit centimeter portion  26  has a height of one centimeter, width  122  is two millimeters. Accordingly, bars  102 - 106  and spaces  108 - 110  can be used to determine a precise offset from the bottom of digit centimeter portion  26 . For example, if reference line  210  (FIG. 5) within the scope appears to lie across the center of upper space  108  (FIG.  4 ), i.e., generally equidistant between top bar  102  and middle bar  104 , the measurement is 0.887 meters. This measurement is the sum of (i) 0.8 meters which is determined by reference to numerical representation  14  (FIG.  1 ); (ii) 0.08 meters which is determined by reference to the numerical representation of digit centimeter portion  26 ; and (iii) 0.007 meters which is determined by reference to the combined widths of bottom bar  106  (FIG.  4 ), lower space  110 , middle bar  104 , and half of upper space  108 . Other digit centimeter portions which represent numbers whose representations have top, middle, and/or bottom horizontal bars are positioned analogously to top bar  102 , middle bar  104 , and bottom bar  106 , respectively, to similarly provide more detailed information regarding offsets within such digit centimeter portions. 
     While digit centimeter portions such as digit centimeter portions  20 ,  22 , and  26  provide reference points for resolutions up to two millimeters and provide a good estimate of single millimeter measurements, greater precision is provided by calibrated centimeter section  24  which is shown in isolation in FIG.  2 . Calibrated centimeter section  24  includes a top bar  26  and a bottom bar  48 . Alignment of a reference line with top bar  26  indicates a measured offset of one full centimeter from the bottom of calibrated centimeter section  24 . While top line  26  may be difficult to see through the scope at times, e.g., when calibration system  10  is placed a significant distance from the scope, alignment between reference line  210  (FIG. 5) and top line  26  (FIG. 2) can be recognized since top line  26  is aligned with the border of digit centimeter portions  20  (FIG. 1) and  22  and that border is relatively easy to perceive, even at significant distances. In addition, calibrated centimeter section  24  (FIG. 2) includes symmetrical stepped sections, one of which is formed by blocks  28  and  30  and a second of which is formed by blocks  38  and  40 . The stepped sections are symmetrical about the center of calibrated centimeter section  24  as marked by a long tick mark and the numeral five which in turn represents a five millimeter offset from the bottom of calibrated centimeter section  24 . 
     Specifically, the upper stepped section includes block  28  which is one millimeter in height and equal in width to the full width of calibrated centimeter section  24 . In addition, block  30  is adjacent to lower edge  30  of block  28 , is one millimeter in height, and has a width equal approximately to one-half of the width of calibrated centimeter section  24 . Together, blocks  28  and  30  form the upper stepped section and define three offset positions within calibrated centimeter section  24 . Specifically, upper edge  36  of block  28  defines an eight-millimeter offset within calibrated centimeter section  24 , i.e., from bottom line  48  which represents a zero-millimeter offset within calibrated centimeter section  24 . Lower edge  32  of block  28  extends significantly beyond block  30  to be exposed and recognizable from significant distance. Lower edge  32  defines a seven-millimeter offset within calibrated centimeter section  24 . Lower edge  34  of block  30  defines a six-millimeter offset within calibrated centimeter section  24 . Edges  36 ,  32 , and  34  are quite different in appearance and are therefore easily distinguishable from one another, even at great distances. As a result, recognition of any numerical reference is generally unnecessary to accurately identify six-, seven-, and eight-millimeter offsets within calibrated centimeter section  24 . 
     The lower stepped section is symmetric with the upper stepped section and includes blocks  38  and  40 . Block  38  is one millimeter in height and equal in width to the full width of calibrated centimeter section  24 . Block  40  is adjacent to upper edge  42  of block  38 , is one millimeter in height, and has a width equal approximately to one-half of the width of calibrated centimeter section  24 . Lower edge  46  of block  38  defines a two-millimeter offset within calibrated centimeter section  24 . Upper edge  42  of block  38  defines a three-millimeter offset within calibrated centimeter section  24 . Upper edge  44  of block  40  defines a four-millimeter offset within calibrated centimeter section  24 . As described above with respect to edges  36 ,  32 , and  34 , edges  46 ,  42 , and  44  are quite different in appearance and are therefore easily distinguishable from one another, even at great distances. As a result, recognition of any numerical reference is generally unnecessary to accurately identify two-, three-, and four-millimeter offsets within calibrated centimeter section  24 . 
     Furthermore, the upper stepped section of blocks  28  and  30  have an appearance which is distinct from the lower stepped section of blocks  38  and  40 . The upper and lower stepped sections are therefore readily distinguished from one another, even a significant distance. For example, a reference line which is aligned at a border between a short block, e.g., either of blocks  30  and  40 , and a long block, e.g., either of blocks  28  and  38 , indicates either a three-millimeter offset or a seven-millimeter offset. Due to the distinct appearances of the upper and lower stepped section, these two are easily distinguished. If the shorter block is above the longer block, reference line  210  (FIG. 5) is aligned with upper edge  42  (FIG. 2) of block  38  and a three-millimeter offset is indicated. Conversely, if the shorter block is below the longer block, reference line  210  (FIG. 5) is aligned with lower edge  32  (FIG. 2) of block  28  and a seven-millimeter offset is indicated. 
     Lower edge  34  of block  30  and upper edge  44  of block  40  are separated by two millimeters. A reference line which appears between and generally equally distant from edges  34  and  44  indicates a five-millimeter offset within calibrated centimeter section  24 . Edges  34  and  44  are easily recognizable as described above. 
     Bottom line  48  represents a zero-millimeter offset within calibrated centimeter section  24 . Bottom line  48  is easily recognized as bottom line  48  is aligned with edges of centimeter portions such as centimeter portion  16  (FIG. 1) and digit centimeter portion  20 . In addition, bottom line  48  is displaced from lower edge  46  by two millimeters such that a reference line which appears above bottom line  48  and below lower edge  46  of block  38  indicates a one-millimeter offset into calibrated centimeter portion  24 . 
     Top line  26  represents a ten-millimeter offset within calibrated centimeter section  24 . Top line  26  is easily recognized as bottom line  48  is aligned with edges of centimeter portions in generally the manner described above with respect to bottom line  48 . In addition, top line  26  is displaced from upper edge  36  by two millimeters such that a reference line which appears below top line  26  and above upper edge  36  of block  28  indicates a nine-millimeter offset into calibrated centimeter portion  24 . 
     Thus, calibrated centimeter section  24  can be used to measure accurately with a precision of one millimeter. 
     An alternative to calibrated centimeter section  24  is shown in FIG.  3 . Tenth-inch section  50  provides accurate measurements with a precision of one-hundredth of an inch. Tenth-inch section  50  includes a bottom line  52  and a top line  84  which are generally analogous to bottom  48  (FIG. 2) and top line  26 , respectively, of calibrated centimeter section  24 . In addition, tenth-inch section  50  (FIG. 3) includes a lower stepped section which includes blocks  54 ,  56 , and  58  and an upper stepped section which includes blocks  70 ,  72 , and  74 . Block  54  is one-hundredth of an inch high and has a bottom edge  60  which is one-hundredth of an inch from bottom line  52 . Accordingly, upper edge  62  of block  52  represents an offset of two-hundredths of an inch from bottom line  52 . Block  54  is equal in width to tenth-inch section  50 . 
     Block  56  is adjacent to block  54  at upper edge  62  and is significantly less wide that block  54 . In one embodiment, block  56  has a width which is approximately two-thirds the width of tenth-inch section  50 . Thus, a significant portion of upper edge  62  is exposed, i.e., is not adjacent to block  56 . Upper edge  62  is therefore easily recognizable from considerable distance and therefore provides a good reference for a two-hundredth inch offset within tenth-inch section  50 . 
     Similarly, block  58  is adjacent to block  56  at upper edge  64  and is significantly less wide that block  56 . In one embodiment, block  58  has a width which is approximately one-third the width of tenth-inch section  50 . Thus, a significant portion of upper edge  64  is exposed, i.e., is not adjacent to block  58 . Upper edge  64  is therefore easily recognizable from considerable distance and therefore provides a good reference for a three-hundredth inch offset within tenth-inch section  50 . 
     Upper edge  66  of block  58  provides a reference for a four-hundredth inch offset within tenth-inch section  50 . Blocks  70 ,  72 , and  74  are substantially equal in dimension to blocks  58 ,  56 , and  54 , respectively, and are adjacent to one another to form an upper stepped section as shown. In particular, block  74  is substantially equal in width to tenth-hundredth section  50  and is one-hundredth of an inch in height. Upper edge  82  is fully exposed, i.e., not adjacent to any other block, and provides a reference for a nine-hundredth inch offset within tenth-inch section  50 . A significant portion of lower edge  80  is exposed to provide a reference for an eight-hundredth inch offset within tenth-inch section  50 . Block  72  is adjacent to block  74  at lower edge  80  and is substantially less wide than block  74 . In one embodiment, block  72  has a width which is approximately two-thirds of the width of tenth-inch section  50 . Block  72  has a height of one-hundredth of an inch, as do all of blocks  54 ,  56 ,  58 ,  70 ,  72 , and  74 . Block  70  is adjacent to lower edge  78  of block  72  but is substantially less wide than block  72  so that a significant portion of lower edge  78  is exposed. In one embodiment, block  70  has a width which is approximately one-third the width of tenth-inch section  50 . Lower edge  78  is therefore easily recognizable from considerable distance and provides a reference to a seven-hundredth inch offset within tenth-inch section  50 . Lower edge  76  of block  70  is fully exposed and provides a reference for a six-hundredth inch offset within tenth-inch section  50 . 
     A five-hundredth inch offset within tenth-inch section  50  is marked by a bar  68  midway between upper edge  66  of block  58  and lower edge  76  of block  70 . A ten-hundredth inch offset within tenth-inch section  50  is marked by a top bar  84  which is one-hundredth of an inch above upper edge  82  of block  74 . Thus, tenth-inch section  50  provides accurate measurements with a precision of one-hundredth of an inch which are optically recognizable from substantial distances. 
     The above description is illustrative only and is not limiting. The present invention is limited only by the claims which follow.