CHAPTER 5. California Orthometric Heights [8890 - 8902]
( Chapter 5 added by Stats. 2005, Ch. 158, Sec. 29.16. )
Orthometric heights within the State of California that are based on the North America Vertical Datum of 1988 and conforming to the provisions of this chapter shall be known as “California Orthometric Heights of 1988.” Orthometric heights are commonly referred to as “elevations.”
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
As used in this chapter:
(a) “NGS” means National Geodetic Survey or its successor.
(b) “CSRC” means California Spatial Reference Center or its successor.
(c) “NAVD88” means North American Vertical Datum of 1988.
(d) “GPS” means Global Positioning System and includes other, similar space-based systems.
(e) “FGDC” means the Federal Geographic Data Committee or its successor.
(f) “FGCS” means the Federal Geodetic Control Subcommittee or its successor.
(g) “CSRN” means California Spatial Reference Network as defined by Chapter 3 (commencing with Section 8850), “Geodetic Datums and the California Spatial Reference Network.”
(h) “COH88” means California Orthometric Heights of 1988.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
The phrase “California Orthometric Heights of 1988” or any abbreviation, such as “COH88,” thereof shall be used only in reference to orthometric heights based on NAVD88 and conforming to the provisions of this chapter.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
COH88 values shall be expressed in meters and decimals of a meter or in feet and decimals of a foot. When COH88 values are expressed in feet, the “U.S. Survey Foot,” (one foot equals 1200/3937 meters) shall be used as the standard foot.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
COH88 values that are determined from differential leveling surveys shall be known as “leveled COH88” values. COH88 values that are determined from GPS surveys and the appropriate application of a geoid model shall be known as “derived COH88” values.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
When a geoid model is used to determine derived COH88 values, it shall be the latest geoid model published by NGS.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
The accuracy of derived COH88 values may be improved by applying a “local orthometric height correction” to the geoid height determined from the latest, applicable geoid model published by NGS.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
The survey that establishes a COH88 value or values shall meet all of the following requirements:
(a) The survey shall be referenced to and shall have field-observed statistically independent connections to one or more orthometric height reference stations that is or are one of the following:
(1) CSRN station.
(2) Geodetic control station located outside of the State of California that meets all the requirements for inclusion in the CSRN except that the station is outside California.
(3) Existing COH88 station that (A) is shown on a map filed with the applicable county surveyor by a public officer, subdivision map, corner record, or record of survey, (B) meets all the requirements for inclusion in the CSRN, except that the station and its data are not published by NGS or CSRC, and (C) has an accuracy, conforming to the applicable CSRN requirements, stated for the station’s value.
(4) Existing COH88 station that is shown on a public map or document that (A) is compiled and maintained by the applicable county surveyor, (B) meets all the requirements for inclusion in the CSRN except that the station and its data are not published by NGS or CSRC, and (C) has an accuracy, conforming to the applicable CSRN requirements, stated for the station’s value.
(b) If an accuracy is to be claimed for the COH88 value or values established, the claimed accuracy shall be an accuracy standard published by FGDC or FGCS.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
If an accuracy is claimed for a COH88 value or values, the survey that established the value or values shall be documented on a map, record of survey, corner record, or other document that includes, at a minimum, the following:
(a) For each COH88 station, the resultant COH88 value.
(b) For each individual COH88 value, whether it is a leveled COH88 or a derived COH88 value.
(c) For leveled COH88 values, the beginning and ending dates of the observations used to determine the values.
(d) For derived COH88 values, the date of the NGS geoid model used to determine the values.
(e) When derived COH88 values are shown and reflect the application of a “local orthometric height correction model,” written data that justifies the model’s validity. Such written data shall include a summary of the procedures, computations, analysis, and validation process used to develop the model.
(f) For derived COH88 values, the epoch (date), in a decimal year format to two decimal places, that is the basis of the COH88 values shown. Said epoch shall be the published NGS or CSRC epoch of a controlling station for the survey.
(g) The FGDC or FGCS accuracy standard of the COH88 value or values established. FGDC accuracies shall be identified as either a local or network accuracy.
(h) Additional written data that justifies the FGDC or FGCS accuracy standard shown. Such additional written data shall include observation equipment, control diagram including required field-observed statistically independent connection or connections, adjustment methodology and software used, a summary of the procedures used or a reference to a published commonly accepted procedural specifications, final residuals or closures, and other data essential for others to evaluate the survey.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
When a COH88 value or values are shown on any document, the document shall include the following:
(a) A statement that the orthometric height or heights shown are a COH88 value or values; exceptions shall be noted.
(b) The station or stations to which the COH88 value or values are referenced and connected and the orthometric height value or values and the published or stated accuracy or accuracies of said referenced station or stations.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
The use of COH88 by any person, firm, or governmental agency is optional.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
This chapter does not impair or invalidate land titles, legal descriptions, or jurisdictional or land boundaries and, further, this chapter does not impair or invalidate references to, or the use of, datums, elevations, orthometric heights, or other height values that do not conform to this chapter except as specified in Section 8892 in this chapter.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)
This chapter does not prohibit the use of new surveying technologies or techniques for which FGCS specifications or other accepted specifications have not yet been published.
(Added by Stats. 2005, Ch. 158, Sec. 29.16. Effective January 1, 2006.)