On one axis you can define any number of axis reference systems, each with its own specific parameters. Axis reference systems are systems for specifying locations on an axis using a specific start point on that axis, a specific measurement method and a specific measurement direction. Axis reference systems also define the cross sections to use at specific intervals when 'thinking' in this reference system.
Figure 1 shows how axis reference systems are defined on an axis. In this example the geometrically defined axis is only a part of the real world axis. Rs1 is a reference system that with inverted direction, Rs2 is in axis direction. The origin offset of the reference systems are always the offsets to the axis origin (no matter where the geometrically defined axis starts).
|
Figure 1: Axis reference systems defined on an axis.
Datum |
Notes |
Origin offset |
Defines the start point of the axis reference system on the axis. This value is always given as sloped offset from the axis' origin and is expressed in the length unit defined by the projected coordinate system on which the axis definition is based. The origin offset must be on the geometrically defined part of the axis. I.e. the start offset for a reference system must be greater or equal than the sloped first point offset defined with the axis. Default is 0. |
Inverted direction |
If set the reference system is oriented contrary to the the axis direction. I.e. the higher the offset expressed in that reference system is the lower the offset to the axis origin will be. Default is No. |
Use horizontal measurement |
If set this reference system express offsets as horizontal offsets. See chapter Horizontal vs. sloped offsets for more details Default is No |
Offset unit conversion factor |
The offsets expressed in an axis reference system are of a specific unit. This factor is the factor to be applied to the offset values expressed in a specific reference system to get the offset in the unit used by the axis on which the reference system is defined. The unit used by the axis is defined by the projected coordinate system on which the axis is defined. This factor must not be zero. Default is 1. Examples: If you want to express positions in an axis reference system in km but the projected coordinate system of the underlying axis is using meter the factor must be set to 1000. If you want to express positions in an axis reference system in feet but the projected coordinate system of the underlying axis is using meter the factor must be set to 0.3048 |
Offset unit abbreviation |
Abbreviation for the unit used for offsets expressed in this reference system. Default is m. |
LCS unit conversion factor |
The LCS position for spatial data given in this reference system is expressed in a specific unit. This factor is the factor to be applied to convert the LCS offset to the unit used by the axis's underlying projected coordinate system. This factor must not be zero. Default is 1. Example: If you want to use feet as unit for measuring offsets in the LCS of an axis reference system but the underlying axis' projected coordinate system is using meters this factor must be set to 0.3048 |
LCS unit abbreviation |
Unit used to express transversal and vertical offset in axis references that refer to this reference system. Default is m. |
Additive constant |
Constant that is included in spatial information based on that reference system. The constant is either given as a horizontal or as as sloped offset (depending on the Use horizontal offset setting). Can be a positive or negative value. The additive unit is the unit of the reference system, i.e. the formula additive constant * Offset unit conversion factor gives the additive constant in meters. Default is 0 |
Table 1: Data specifying an axis reference system
