A map projection is a means of projecting the spherical earth onto a flat plane.
There are numerous projection methods available, OziExplorer supports the more common these. If there is a need for a projection not supported a request to the author of the software may result in it being included in future versions.
It is essential that the correct map projection be specified. In many cases the projection is not given or the projection is given but not the required parameters, in these cases it is very difficult to work out what to use.
Also be aware then many maps in digital form may have had the projection altered during the imaging process, as an example many of the US DRG maps have been reprojected from Polyconic to Transverse Mercator (actually UTM format).
This is a projection where the lines of latitude and longitude are projected as
straight lines at 90 degrees to each other.
It is also used for calibrating a map in the shareware version or in the registered
version if the true projection is not known.
Commonly used in marine charts. The rhumb lines (lines of constant bearing) are straight lines. The latitude and longitudes are straight lines which meet at right angles.
The Transverse Mercator projection is very commonly used for topographic maps and is the projection you are most likely to be using. The map is projected from a central meridian (line of longitude) which is straight, the equator (a line of latitude is also straight) all other lines of longitude and latitude are curved. Scale exaggeration increases the further away from the central meridian, this projection therefore is only useful for a small region either side of the central meridian. Since most maps we use only cover a relatively small region or zone these errors induced by the scale change are too small to be important.
Also know as the Gauss Conformal Cylindrical projection.
Many common grid systems are based on the Transverse Mercator projection such as UTM, Gauss Krueger, German Grid, Dutch Grid, Israeli Grid. All these grids can be setup in the User Grid.
The following parameters are required to use a map with a Transverse Mercator Projection. These parameters are sometimes referred to as a User Grid.
Latitude Origin - may be zero (0) degrees
Central Meridian - Must be known for your particular map
Scale Factor - used to set up a grid system
False Easting - used to set up a grid system
False Northing - used to set up a grid system
The UTM is not really a projection in its own right but is a Grid coordinate system based on a special case of the Transverse Mercator projection. The Latitude origin is set at 0 degrees; the Central Meridian is the centre of one of the 60 UTM zones which circle the earth 6 degrees apart; the scale factor is set at 0.9996; the False Easting is set at 500000; the False Northing is set at 0 for the northing hemisphere and 10000000 for the southern hemisphere.
The Central Meridian is calculated by OziExplorer based on your calibration points.
The BNG is a Grid coordinate system based on the Transverse Mercator projection, all required parameters to set up the projection are automatically used. Also known as the OSGB grid.
The IG is a Grid coordinate system based on the Transverse Mercator projection, all required parameters to set up the projection are automatically used.
This is a specific projection and a grid system only used by New Zealand. All required parameters are known.
This is a specific projection and a grid system only used by New Zealand. All required parameters are known.
The Swedish Grid is a Grid coordinate system based on the Transverse Mercator projection, all required parameters are known.
This is a specific projection and a grid system only used by Switzerland. All required parameters are known.
A sterographic projection which gives good directional and shape relationships, useful for large scale mapping. Used for air navigation and meteorological charts.
You need to enter the 2 lines of Latitude and the Central Meridian which are required to calculate this projection, these must be known for the particular map you are using.
Sometimes the projection can be specified with only 1 line of Latitude, since oziExplorer expects there to be 2 lines of latitude specified which are different values simply enter one of the values as a slightly different number (say add .000001 of a minute to the value).
The lines of latitude are straight and equally spaced. The Central Meridian is straight all other lines of longitude are curved. Good projection for large continental sized areas.
You need to enter the Central Meridian for the particular map you are using.
Polyconic (American)
Preserves area,shape, distance and azimuth for small areas, best for north-south extents. Former projection for US topographic maps, not recommended for larger areas because of distortion.
You need to enter the Central Meridian for the particular map you are using.
Albers Equal Area
Best for maps of east-west extents away from the equator, one of the most commonly used projections for maps of conterminous USA.
You need to enter the 2 lines of Latitude and the Central Meridian which are required to calculate this projection, these must be known for the particular map you are using. The Latitude Origin may also be required but defaults to zero degrees.