LVL_DH

The LVL_DH program computes the expected leveled difference in height between two North American Vertical Datum of 1988 (NAVD 88) bench marks.

Bench marks of NAVD 88 constitute the official national vertical datum for mapping and charting, and provide a vertical reference for the national infrastructure. Thus, surveyors frequently use these bench marks for reference points and to check their measurements. Leveled height differences (dh) do not strictly correspond to orthometric height differences (dH), because the nonparallelism of level surfaces is not reflected in the leveling measurements collected in the field (see figure); e.g., å dh (dh₁+dh₂+dh₃) ¹ ådH (dH₁+dH₂+dH₃) between bench marks A and B, where ådH = H_B – H_A. In contrast to leveled heights, adjusted NAVD 88 heights published by the National Geodetic Survey (NGS) are defined in the same Helmert orthometric vertical system as the orthometric heights obtained through the Global Positioning System (GPS) measurements and the proper geoid height value (apart from occasional small system shifts), such as the values provided by GEOID99.

Program LVL_DH converts the published orthometric height difference between two NAVD 88 bench marks into a leveled height difference by removing the orthometric correction from the published relative height.

• Documentation
• Download the LVL_DH program and related files for PC execution.
• Interactively compute a Leveled Difference between two NAVD 88 benchmarks.

See the PDF version of an article about LVL_DH that appeared in the Professional Surveyor magazine, July 2003 Volume 23, Number 7

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