# US 11,112,271 B2 · Method of calibrating a computerized leveling offset meter

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- Number: US 11,112,271 B2
- Document ID: US11112271B2
- Status: Granted
- Kind: B2
- Application number: 16/332,342
- Filed: 2017-09-24
- Published: 2019-08-01
- Granted: 2021-09-07
- Earliest claimed: 2016-09-25
- Assignees: Israel Aerospace Industries Ltd.
- Applicants: Israel Aerospace Industries Ltd.
- Inventors: Aharon Yifrach; Roey Zuitlin
- Web page: https://patentgrep.com/patent/US11112271B2

## CPC

- G01C 25/00: Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass (testing, calibrating or compensating compasses G01C17/38)
- G01C 9/32: Means for facilitating the observation of the position of the bubble, e.g. illuminating means
- G01C 9/36: of the spherical type, i.e. for indicating the level in all directions
- G01V 13/00: Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)

## Abstract

A method of calibrating a levelling offset meter (LOM) for calculating the angular offset between a plane parallel to the LOM and a predetermined reference plane, the LOM comprises a bull's eye spirit level having a bubble and a processor coupled to an image, comprising: capturing, by the imager, a plurality of images of the spirit level associated with a respective plurality of known angular offsets; calculating in respect of each image a pixel distance from the bubble center to a predetermined zero offset pixel, thereby obtaining a plurality of pixel distances, each pixel distance associated with a known angular offset; fitting a function to a plurality of pairs of values, each pair of values comprising a pixel distance and its associated known angular offset; and storing the function in a memory.

## Claims

### Claim 1

A method of calibrating a levelling offset meter (LOM) for calculating the angular offset between a plane parallel to the LOM and a predetermined reference plane, the LOM comprising a bull's eye spirit level having a bubble therein, and a processor operatively coupled to an imager, the method comprising:
capturing, by the imager, a plurality of images of the spirit level, the plurality of images associated with a respective plurality of known angular offsets, each image being captured while the LOM is oriented with respect to the predetermined reference plane at the known angular offset associated with the image;
calculating, by the processor, in respect of each image, a pixel distance from the bubble center to a predetermined zero offset pixel, thereby obtaining in respect of the plurality of images a plurality of pixel distances, each pixel distance associated with a known angular offset;
fitting, by the processor, a function to a plurality of pairs of values, each pair of values comprising a pixel distance and its associated known angular offset, said function being useable to map a new pixel distance obtained in respect of a new image to a corresponding angular offset between a plane parallel to the LOM and the predetermined reference plane; and
storing the function in a memory.

### Claim 2 (depends on 1)

The method of claim 1 wherein the pixel distance comprises an x-pixel distance and a y-pixel distance, and wherein the angular offset comprises a pitch offset and a roll offset.

### Claim 3 (depends on 2)

The method of claim 2 wherein fitting a function to a plurality of pairs of values comprises fitting a first function to a first plurality of pairs of values and fitting a second function to a second plurality of pairs of values, wherein each pair of values in the first plurality of pairs of values comprises an x-pixel distance and a corresponding pitch offset, and each pair of values in the second plurality of pairs of values comprises a y-pixel distance and a corresponding roll offset.

### Claim 4 (depends on 1)

The method of claim 1, wherein the zero offset pixel is determined by:
capturing, by the imager, a plurality of images of the bubble whilst the levelling offset meter is rotated along a rotation axis orthogonal to the predetermined reference plane, the plurality of images captured at a respective plurality of degrees of rotation;
for each image, determining, by the processor, a first pair of values indicative of the pixel coordinates of the pixel closest to the bubble center, thereby determining a plurality of first pairs of values corresponding to a respective plurality of images;
calculating, by the processor, a second pair of values based on said plurality of first pairs of values and indicative of a midpoint of all said first pairs of values, and
selecting the pixel having pixel coordinates corresponding to the second pair of values as the zero offset pixel.

### Claim 5

A processor configured to execute a series of operations for calibrating a levelling offset meter (LOM) for calculating the angular offset between a plane parallel to the LOM and a predetermined reference plane, the LOM comprising a bull's eye spirit level having a bubble therein, the processor operatively coupled to an imager configured to image the spirit level, the series of operations comprising:
calculating, in respect of each of a plurality of images of the spirit level image, a pixel distance from the bubble center to a predetermined zero offset pixel, thereby obtaining in respect of the plurality of images a plurality of pixel distances, each pixel distance associated with a known angular offset, each image being captured by the imager while the LOM is oriented with respect to the predetermined reference plane at the known angular offset associated with the image;
fitting a function to a plurality of pairs of values, each pair of values comprising a pixel distance and its associated known angular offset, said function being useable to map a new pixel distance obtained in respect of a new image to a corresponding angular offset between a plane parallel to the LOM and the predetermined reference plane; and
storing the function in a memory.

### Claim 6 (depends on 5)

The processor of claim 5, wherein the pixel distance comprises an x-pixel distance and a y-pixel distance, and wherein the angular offset comprises a pitch offset and a roll offset.

### Claim 7 (depends on 6)

The processor of claim 6 wherein fitting a function to a plurality of pairs of values comprises fitting a first function to a first plurality of pairs of values and fitting a second function to a second plurality of pairs of values, wherein each pair of values in the first plurality of pairs of values comprises an x-pixel distance and a corresponding pitch offset, and each pair of values in the second plurality of pairs of values comprises a y-pixel distance and a corresponding roll offset.

### Claim 8 (depends on 5)

The processor of claim 5, wherein the processor is configured to determine the zero offset pixel using a plurality of images of the bubble captured by the imager whilst the levelling offset meter is rotated along a rotation axis orthogonal to the predetermined reference plane, the plurality of images captured at a respective plurality of degrees of rotation, by:
for each image, determining a first pair of values indicative of the pixel coordinates of the pixel closest to the bubble center, thereby determining a plurality of first pairs of values corresponding to a respective plurality of images;
calculating a second pair of values based on said plurality of first pairs of values and indicative of a midpoint of all said first pairs of values, and
selecting the pixel having pixel coordinates corresponding to the second pair of values as the zero offset pixel.

### Claim 9

A computer program product comprising a program of instructions readable by a computer, the program of instructions for executing a method of calibrating a levelling offset meter (LOM) for calculating the angular offset between a plane parallel to the LOM and a predetermined reference plane, the LOM comprising a bull's eye spirit level having a bubble therein, and a processor operatively coupled to an imager, the method comprising:
capturing, by the imager, a plurality of images of the spirit level, the plurality of images associated with a respective plurality of known angular offsets, each image being captured while the LOM is oriented with respect to the predetermined reference plane at the known angular offset associated with the image;
calculating, by the processor, in respect of each image, a pixel distance from the bubble center to a predetermined zero offset pixel, thereby obtaining in respect of the plurality of images a plurality of pixel distances, each pixel distance associated with a known angular offset;
fitting, by the processor, a function to a plurality of pairs of values, each pair of values comprising a pixel distance and its associated known angular offset, said function being useable to map a new pixel distance obtained in respect of a new image to a corresponding angular offset between a plane parallel to the LOM and the predetermined reference plane; and
storing the function in a memory.

### Claim 10 (depends on 9)

The computer program product of claim 9 wherein the pixel distance comprises an x-pixel distance and a y-pixel distance, and wherein the angular offset comprises a pitch offset and a roll offset.

### Claim 11 (depends on 10)

The computer program product of claim 10 wherein fitting a function to a plurality of pairs of values comprises fitting a first function to a first plurality of pairs of values and fitting a second function to a second plurality of pairs of values, wherein each pair of values in the first plurality of pairs of values comprises an x-pixel distance and a corresponding pitch offset, and each pair of values in the second plurality of pairs of values comprises a y-pixel distance and a corresponding roll offset.

### Claim 12 (depends on 9)

The computer program product of claim 9, wherein the zero offset pixel is determined by:
capturing, by the imager, a plurality of images of the bubble whilst the levelling offset meter is rotated along a rotation axis orthogonal to the predetermined reference plane, the plurality of images captured at a respective plurality of degrees of rotation;
for each image, determining, by the processor, a first pair of values indicative of the pixel coordinates of the pixel closest to the bubble center, thereby determining a plurality of first pairs of values corresponding to a respective plurality of images;
calculating, by the processor, a second pair of values based on said plurality of first pairs of values and indicative of a midpoint of all said first pairs of values, and
selecting the pixel having pixel coordinates corresponding to the second pair of values as the zero offset pixel.