Datum USE Methods

Australia has adopted the techniques developed by Geomatics Canada for its National Transformation (Version 2) to define a precise means of converting from the Australian Geodetic Datum of 1966 to the newer Geocentric Datum of Australia 1994. The data files involve overlap, and those areas deserve special attention.

Datum shift data files for this transformation are being developed on a state-by-state basis. Therefore, there is more than one data file for this transformation. The coordinate conversion system considers AGD66 to be a single entity even though there are several different data files that overlap. Users are encouraged to sort data files to ensure that the desired data file is used in the regions of overlap.

This is the same as the ASTRLA66-Grid_to_WGS84 transformation.

Several of the states in Australia have been using the Australian Geodetic Datum of 1984 for some time now. This transformation technique implements the conversion of AGD84 to GDA 1994. Operationally, this technique is identical to the AGD66 to GDA94; however, different data files are used. See AGD66 to GDA94 via Grid File for more details.

This is the same as the ASTRLA84-Grid_to_WGS84 transformation.

The Average Terrestrial System of 1977 has been used in the Maritime provinces of Canada since 1977. This transformation uses data files in the Canadian National Transformation (version 2) format to determine the shift required to properly transform ATS77-based geographic coordinates to CSRS-based coordinates. Note that:

• Each of the different provinces involved have produced a data file covering the geography of their respective provinces, and
• The individual data files are not in the public domain and must be obtained by users directly from the provincial governments involved.

This is the same as the ATS77_to_WGS84 transformation.

Switzerland has adopted the Canadian technique to define the shift from CH1903 to CH1903+.

This is the same as the CH1903/GSB_to_WGS84 transformation.

CSRS (Canadian Spatial Reference System) is the Canadian equivalent to the U.S.'s HARN; that is, a very accurate rework of NAD83 using GPS technology. This transformation allows direct conversion of NAD27 data to CSRS, without making a stop at NAD83. This conversion technique is implemented by a series of datum shift grid files of the Canadian National Transformation format. Unlike other Canadian implementations, however, there are multiple overlapping files involved.

You can choose a fallback transformation to specify how data points outside the coverage of existing data files are to be handled. Data files are being generated on a province-by-province basis. Individual files may not be in the public domain. You may need to acquire the appropriate data files in order to use the transformation.

This is equivalent to the NAD27_to_CSRS_FME transformation, reversed.

CSRS (Canadian Spatial Reference System) is the Canadian equivalent to the U.S.'s HARN; that is, a very accurate rework of NAD83 using GPS technology. Like the US HARN, the shifts are in the range of 1 to 2 feet (40 centimeters).

This conversion technique is implemented by a series of datum grid shift files of the Canadian National Transformation format. Unlike other Canadian implementations, however, there are multiple overlapping files involved.

You can choose a fallback transformation to specify how data points outside the coverage of existing data files are to be handled.

Data files are being generated on a province-by-province basis. Individual files may not be in the public domain. You may need to acquire the appropriate data files in order to use the transformation.

This is equivalent to the CSRS_to_WGS84 transformation.

German authorities have published a grid shift data file for transforming DHDN to ETRS89, applicable to German geography. Although this file covers all of Germany, it is appropriate only for specific uses.

This is equivalent to the DHDN/BeTA_to_WGS84 transformation.

Spain has adopted the Canadian technique to define the shift from the European Datum of 1950 (ED50) to European Terrestrial Reference Frame, 1989 (ETRF89).

This is equivalent to the ED50-IGN.ES_to_WGS84 transformation.

Deprecated. This method produced incorrect results until FME2013, when support was removed.

For more information, see Geographic Transformations.

The differences between GDA94 and WGS84 are small. Further, a generally accepted means of converting between GDA94 and WGS84 is unknown to the authors of the coordinate conversion system. This technique does nothing.

This is equivalent to the GDA94_to_WGS84 transformation.

HARN (High-Accuracy Reference Network) has also been known as HPGN (High-Precision GPS Network): both terms refer to NAD83/91, which is a rework of NAD83 with the aid of GPS technology (since GPS was not functional in 1983). This technique selection implies the use of the algorithms and data files of the U. S. National Geodetic Survey's NADCON program to effect the shift between NAD83 and HARN.

As with the NADCON technique, this transformation relies on the existence of data files that define the shift at various geographic points in a grid format. As is the case with the NAD27/NAD83 NADCON data files, these data files come in pairs and are in the public domain.

All of the data files used in this transformation adhere to a specific naming convention (as published by the National Geodetic Survey): they must have the proper .LAS and .LOS extensions, and the names and locations must be properly recorded in the Geodetic Data Catalog file. These files all overlap their neighbors by a substantial amount.

Since different results for the same point can be obtained depending upon which specific data files are used, users should pay significant attention to the order and choice of files. For example, if the geography one is working with is primarily in Ohio, then the Ohio HPGN file should be listed first in the catalog file. This will cause that data file to take precedence over all others in the case of overlap.

Users can choose a fallback transformation to specify a fallback definition to be used when coordinate data not covered by the data files is processed.

This is equivalent to the HPGN_to_WGS84 transformation.

This method is used to transform data from the older Tokyo Datum to the Japanese Geodetic Datum of 2000 (JGD2K). Associated data files define the transformation, and must be purchased from the Geographic Institute of Japan.

The data files, as supplied by the Geographic Institute of Japan, are in the form of text files, with no guarantee of records of fixed length, and which are not in any specific order. Since the most popular of these files covers all of Japan, the size of this particular file is quite large (approximately 12 MB). FME will, therefore, convert the text file into a binary form upon its first use.

This is equivalent to the JPNGSI-Grid_to_WGS84 transformation.

The local DHDN to ETRS89 grid shift is used to transform coordinates in a more precise scale than the DHDN to ETRS89 grid shift and does not necessarily cover all of Germany.

This transformation must be configured to point to the user-provided Grid Shift Binary (gsb) files required to execute the particular NTv2 transform required. To make the change, click Tools > FME Options > Coordinate Systems.

This is equivalent to the DHDN/local_to_WGS84_local_grid_FME transformation.

Austrian authorities have published a grid shift data file for transforming MGI to ETRS89, applicable to Austrian geography. This covers all of Austria.

This transformation must be configured to point to the Grid Shift Binary file AT_GIS_GRID.gsb. To make the change, click Tools > FME Options > Coordinate Systems. You can also place the AT_GIS_GRID.gsb file in the default location:

<FME_Install_folder>/Reproject/GridData/Austria/AT_GIS_GRID.gsb.

This file, available freely at the website of the Austrian Federal Office for Metrology and Survey, https://www.bev.gv.at, is required to execute the particular NTv2 transform required.

This is equivalent to the MGI/Grid_to_WGS84_FME transformation.

This transformation represents the integration of the algorithms originally published by the National Geodetic Survey of the US and Geomatics Canada in the forms commonly known as the NADCON program and the National Transformation (Versions 1 and 2). That is, this transformation is the means by which one would convert from the North American Datum of 1927 (NAD27) to the North American Datum of 1983 (NAD83).

All of the techniques encapsulated in this transformation rely on access to data files that define the amount of the shift from NAD27 to NAD83 in a grid form. The coordinate conversion system uses algorithms identical to those used by the respective government-published programs to interrogate the data files and determine the shift for any given coordinate.

The shift data is stored in a single data file for the Canadian National Transformation (either version) and neither of these data files is in the public domain. The recommended NTv2 file is distributed with FME. In the case of the US NADCON data files, two files are required for each region covered. One file contains the latitude shift and the second contains the longitude shift. These files are in the public domain and are usually included in the distribution of this product. Should updates become available, you can use the data files in the exact form as they are published by the National Geodetic Survey.

Since the coverage of the data files is limited, the coordinate conversion system uses a fallback technique to calculate datum shifts for coordinates that are not covered by the data files.

Depending on the US/Canada preference chosen for FME, this is equivalent to NAD27_to_WGS84 or NAD27_to_WGS84_Canada_FME.

France has developed a technique to define the shift from the New Triangulation of France Datum (NTF) to Reference Geodesique pour la France (RGF93). This technique makes use of a single grid file called gr3df97a.txt which must be placed in the FME's Reproject folder to work. For all intents and purposes, RGF93 is considered equivalent to WGS84.

This is equivalent to the NTF-G-Grid_to_WGS84 transformation.

Currently, the differences between NZGD2K and WGS84 are small. Further, a generally accepted means of converting between NZGD2K and WGS84 is unknown to the authors of the coordinate conversion system. This technique does nothing.

This is equivalent to the NZGD2000_to_WGS84 transformation.

New Zealand has adopted the Canadian technique to define the shift from the New Zealand Geodetic Datum of 1949 (NZGD49) to New Zealand Geocentric Datum of 2000 (NZGD2K). This implementation is somewhat simpler in that only a single data file is used.

This is equivalent to the NZGD49_to_WGS84 transformation.

The ROME1940 to IGM95 grid shift is used to transform coordinates between these two datums used in Italy.

This transformation must be configured to point to the user-provided Grid Shift Binary file R40WGS_t.gsb to execute the particular NTv2 transform required. To make the change, click Tools > FME Options > Coordinate Systems. You can also place theR40WGS_t.gsb file in the default location:

<FME_Install_folder>/Reproject/GridData/Italy/R40WGS_t.gsb.

This is equivalent to the MonteMario_Grid_to_WGS84_FME transformation.