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To achieve precise distance measurements, especially in surveying and construction, certain corrections must be applied to account for potential sources of error like the standardization errors, temperature variations, and slope adjustments.Standardization error emerges when measurement equipment undergoes changes, such as wear, repairs, or weather impacts. To address this, surveyors compare the equipment’s readings to a standard. This process identifies any deviation that might lead to...
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Errors in Taping01:18

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Errors in taping arise from multiple factors that can significantly impact measurement accuracy in surveying. Misalignment of the tape, often due to human error, is one primary source. A skilled rear tapeman, using a telescope, can help correct alignment by guiding the head tapeman; however, human limitations still lead to small inaccuracies. These errors may include misplacement of pins or inaccurate tape readings due to common visual confusions, such as mistaking a six for a nine. Such...
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In the site survey of a four-sided traverse, internal angles are essential to ensure geometric accuracy. The survey revealed that the sum of the measured internal angles was 359 degrees and 48 minutes, which is 12 minutes less than the expected 360 degrees. This discrepancy signals an error likely arising from measurement inaccuracies during the fieldwork.To rectify this error, the adjustment process involved distributing the 12-minute shortfall equally across the four internal angles. By...
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Common Leveling Mistakes and Errors01:17

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A survey team is tasked with determining the elevation difference between points Point A and Point B, separated by uneven terrain. They use a leveling instrument and a leveling rod.Common MistakesMisreading the Rod: During a backsight reading at Point A, the instrumentman observes the rod partially obscured by tall grass. Instead of reading 1.135 m, they mistakenly record 1.735 m due to the misalignment of the crosshair with the wrong graduation. This error adds 0.600 m to all subsequent...
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Influence of Earth's Curvature and Atmospheric Refraction on Leveling01:26

Influence of Earth's Curvature and Atmospheric Refraction on Leveling

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During leveling, the Earth's curvature and atmospheric refraction introduce deviations in the line of sight from a true horizontal reference. When the line of sight is leveled, it remains perpendicular to the plumb line only at a single point. Beyond this, it deviates due to the Earth’s curvature, represented by the correction C. For a sight distance D, the deviation can be derived using the relationship:This relationship shows that the deviation increases quadratically with distance. Over a...
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Related Experiment Video

Updated: Nov 7, 2025

Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating
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Correction of aberration-induced phase errors in phase measuring deflectometry.

Xiangchao Zhang, Zhenqi Niu, Junqiang Ye

    Optics Letters
    |April 30, 2021
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    Summary
    This summary is machine-generated.

    This study introduces a new method to correct phase errors in phase measuring deflectometry for complex optical surfaces. By modeling blurring effects, measurement accuracy for aspheric surfaces was improved threefold.

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    Area of Science:

    • Optical Metrology
    • Surface Characterization
    • Image Processing

    Background:

    • Phase measuring deflectometry (PMD) is vital for complex optical surface measurement.
    • Defocus and aberrations in imaging systems blur fringe images, degrading phase accuracy.
    • Accurate surface normal vector calculation is crucial for optical component manufacturing.

    Purpose of the Study:

    • To develop a method for correcting phase errors in PMD caused by image blurring.
    • To enhance the measurement accuracy of complex optical surfaces, particularly aspheric ones.
    • To mitigate the impact of defocus and system aberrations on phase retrieval.

    Main Methods:

    • Modeling space-variant point spread functions (PSFs) using a skew-normal function.
    • Estimating phase bias through forward convolution of captured images with PSF models.
    • Applying the correction method to a highly curved aspheric surface.

    Main Results:

    • The developed method effectively corrects phase errors caused by image blurring.
    • Measurement accuracy was improved by a factor of three for a highly curved aspheric surface.
    • The skew-normal function accurately models the space-variant blurring effects.

    Conclusions:

    • The proposed phase error correction technique significantly enhances PMD accuracy for challenging optical surfaces.
    • This method offers a robust solution for improving the reliability of optical metrology.
    • Accurate characterization of complex optical surfaces is achievable with this advanced approach.