EPSG Dataset :: v12.054

Vertical Offset by Grid Interpolation (NRCan byn) [DEPRECATED]

Coordinate Operation Method Details [DEPRECATED]

Name:

Vertical Offset by Grid Interpolation (NRCan byn)

Code:

1112

Operation is Reversible:

Yes

Formula:

The relationship between two gravity-related coordinate reference systems may be available through gridded data files of offsets (sometimes called height differences).

The vertical offset at a point is first interpolated within the grid of values using bi-linear interpolation. For interpolation within the offset grid, horizontal positions in the Interpolation CRS are used.

The interpolated value is then applied as a correction parameter A. The interpolated offset is added to the height in the source CRS:
H2 = H1 + A1>2
where
H2 = value in the target vertical coordinate reference system.
H1 = value in the source vertical coordinate reference system.
A1>2 is the offset to be applied for the transformation from CRS 1 to CRS 2. Its value for the forward calculation is the value of the origin of the source CRS 1 in the target CRS 2.

For the reverse transformation from CRS 2 to CRS 1, the same formula is used but with the sign of the offset A1>2 reversed:
H1 = H2 + (–A1>2)

Care! In the EPSG Dataset, offsets are additive (for the forward transformation). See EPSG Guidance Note 7-2, Implementation Notes - Offsets.

Example:

For a point at 49°53'09.293"N, 99°54'41.057"W referenced to NAD83(CSRS)v6 (CRS code 8252) with CGVD28 height of 397.140 metres, to find its CGVD2013(CGG2013a) epoch 2010 height:

First obtain the offsets at each of the surrounding grid nodes by interpolation of the HT2_2010_CGG2013a.byn grid file. Then using biquadratic interpolation for 49°53'09.293"N, 99°54'41.057"W, the offset = -0.382 m.

Then CGVD2013(CGG2013a) epoch 2010 height = 397.140 + (-0.382) = 396.758 m.

For the reverse calculation to find the CGVD28 height from CGVD2013(CGG2013a) epoch 2010 height of 396.758 m:

First interpolate the grid as for the forward transformation. Offset = -0.382 m.

Then CGVD28 height = 396.758 - (-0.382) = 397.140 m.

Method
Parameters:

Parameter Name	Parameter Code	Sign reversal	Parameter Description
Vertical offset file	8732	Yes	The name of the [path and] file containing vertical offsets, the differences in gravity-related height.
EPSG code for Interpolation CRS	1048	No	The EPSG code for the CRS that should be used to interpolate gridded data.

Meta Data

Information Source:

EPSG guidance note #7-2, https://epsg.org

Data Source:

EPSG

Revision Date:

June 29, 2022

Change ID:

[2022.042] [2023.054]

Deprecations:

Deprecation Date	ChangeId	Replaced By	Reason
December 16, 2023	[2023.054]	Vertical change by geoid grid difference (NRCan) (1126)	Method applied interpolated height difference in opposite direction to the sense of the value in the file.

Wildcard	Example
% or *	Any wildcard characters
? or _	One wildcard character
[ - ]	[ - ] Range e.g. N[a-c] will return all geodetic objects that contains a string starting with the letter 'N' or 'n' followed by any of the letters contained within the range specified within the square bracket, e.g. letters a, b and c.
\|	Or e.g. E[a\|e]M will return all geodetic objects that contains a string starting with the letter E(e), ends with the letter M(m) and also contain either the letter a or letter e.