MapRequest defines the coordinate system of a map in terms of its datum (model of the earth) and projection (the manner in which the curved surface of the earth is represented on a flat map). The datum and projection of a map are defined in the map’s .properties file (generally using the datum and projection parameters). To use a supported datum or projection, the name must exactly match one of the datums or projections listed here.
This list is current as of version 1.0.
|
MapRequest datum |
Name |
Comments |
|
AGD66 |
Australian Geodetic Datum 1966 |
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AGD84 |
Australian Geodetic Datum 1984 |
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GD49 |
New Zealand Geodetic Datum 1949 |
|
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GDA |
Geocentric Datum for Australia |
Equivalent to WGS84 |
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NAD83 |
North American Datum 1983 |
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OSGB |
Ordinance Survey Great Britain |
Generally used with the BNG projection |
|
WGS84 |
World Geocentric System 1984 |
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This list is current as of version 1.0.
|
MapRequest projection |
Name |
Comments |
|
BNG |
British National Grid |
MapRequest computes the alphabetic zone identifier from the most significant digit of the northing and easting. |
|
HK80 |
Hong Kong 1980 |
Represented as a custom Transverse Mercator grid in Ozi |
|
IL East |
IL East (USA) State Plane |
Measured in metres |
|
IL East Feet |
IL East (USA) State Plane |
Measured in US survey feet. |
|
latitude/longitude |
Latitude/Longitude |
|
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NY West |
NY West (USA) State Plane |
Measured in metres. |
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NY West Feet |
NY West (USA) State Plane |
Measured in US survey feet. |
|
NZG |
New Zealand Grid |
Lat/long measurements (where required) use a UTM approximation of NZG. |
|
South Africa Lo 17 |
South Africa Transverse Mercator (17 degrees midpoint) |
Represented as a custom Transverse Mercator grid in Ozi. |
|
South Africa Lo 19 |
South Africa Transverse Mercator (19 degrees midpoint) |
Represented as a custom Transverse Mercator grid in Ozi. |
|
South Africa Lo 21 |
South Africa Transverse Mercator (21 degrees midpoint) |
Represented as a custom Transverse Mercator grid in Ozi. |
|
South Africa Lo 23 |
South Africa Transverse Mercator (23 degrees midpoint) |
Represented as a custom Transverse Mercator grid in Ozi. |
|
South Africa Lo 25 |
South Africa Transverse Mercator (25 degrees midpoint) |
Represented as a custom Transverse Mercator grid in Ozi. |
|
South Africa Lo 27 |
South Africa Transverse Mercator (27 degrees midpoint) |
Represented as a custom Transverse Mercator grid in Ozi. |
|
South Africa Lo 29 |
South Africa Transverse Mercator (29 degrees midpoint) |
Represented as a custom Transverse Mercator grid in Ozi. |
|
South Africa Lo 31 |
South Africa Transverse Mercator (31 degrees midpoint) |
Represented as a custom Transverse Mercator grid in Ozi. |
|
UTM |
Universal Transverse Mercator |
MapRequest requires the zone and hemisphere parameters specified. |
|
VICGRID66 |
Victoria (Australia) grid system. (1966 version) |
Equivalent to “VICGRID” in OziExplorer. |
|
VICGRID94 |
Victoria (Australia) grid system. (1994 version) |
Represented as Lambert Conformal Conic in OziExplorer. |
Each datum or projection is defined in its own .txt file in the cs (for coordinate systems) folder (under the folder where MapRequest is installed). Files defining a datum end in _datum.txt, and files defining a projection end in _projection.txt. MapRequest uses the GeoTools package to do coordinate system transformations, and as such it requires the WKT (Well Known Text format) definition of each datum or projection.
A file defining a datum or projection consists of a number of lines, each in the form:
parameter=value
A datum or projection must define both the “name” and “wkt” parameters. Here is a full list of recognised parameters (current as at 1.0b2):
name
The name of the datum or projection in MapRequest (as used by the datum or projection parameters in the map’s .properties file). A datum or projection must have a unique name.
wkt
The WKT (Open GIS Well Known Text format) representation of the datum or projection. Note that datum files will normally define a GEOGCS[], and projection files will normally define only a PROJECTION[]. MapRequest will combine these in an appropriate manner to produce a PROJCS[] (unless the “latitude/longitude” projection is used).
oziexplorer
The name of the datum or projection in OziExplorer (optional).
oziexplorer_code (datums only)
If required, this can be used to specify the base datum in OziExplorer (generally blank or “WGS 84”).
oziexplorer_projection_params (projections only)
If the projection requires parameters in OziExplorer (e.g. for Transverse Mercator or Lambert Conformal Conic) then they can be specified using this parameter. E.g. oziexplorer_projection_params=40.000000000,-78.583333333,0.999937500,350000.00,0.00,,,,,
oziexplorer_unit_multiplier (projections only)
If the projection is a grid system that uses units other than metric metres (e.g. US Survey Feet) then the multiplier between the units the projection uses and metres is specified here. E.g. oziexplorer_unit_multiplier=0.304800609601219
oziexplorer_use_latlong_for_grid (projections only)
If the projection is a custom grid system, but OziExplorer does not allow this type of map to be calibrated using grid coordinates, set “oziexplorer_use_latlong_for_grid=true” to get MapRequest to write the calibration points using latitude/longitude.
If a datum or projection name is specified in a map’s .properties file that MapRequest does not recognise, MapRequest can still work with the map, but some functions will be disabled. MapRequest will not calculate the latitude/longitude for the map corners (for moving map mode in OziExplorer), and it will not calculate the metres/pixel (map scale) value.
When writing a calibration file, MapRequest will use the name specified in the map’s .properties file (either datum or projection as appropriate) as the name for OziExplorer.