Setting a Local Coordinates System

1) Introduction

2) Setting a local coordinates system

• Setting local coordinates in NAVconfig
• Setting local coordinates in NAVdisplay

3) Use of local coordinates with RT-Range systems

• Multiple local coordinates systems
• Local reference system and hunter reference system

4) Local coordinates in post-processing

5)How is local coordinates data calculated 

 

1) Introduction

OxTS navigation units can output several measurements in a local coordinates system defined by the user.

In order to set a local coordinates system, two main things are required:

1. The origin (“zero point”) of the local system: the latitude, longitude and altitude values for the origin must be known. This origin point must be in the same area as the test, within a few miles.
2. The orientation (directions) of the local system’s axes: it is sufficient to set the direction of the X-axis, the Y-axis is always normal to X and pointing to the left of it (as in a cartesian diagram), the Z-axis is always normal to X and Y and pointing up.

 

2) Setting a local coordinates system

The local coordinates system must be defined and saved on the navigation unit. This could be done in NAVconfig and in NAVdisplay:

 

Setting local coordinates in NAVconfig:

• Power the unit and connect to it.
• Open NAVconfig. Select the unit you wish to set the local coordinates on.
• Go to the "Options" page and select "Local coordinates"

• The following window will open up:

• Enable the local coordinates, then type in the origin point values. You can use the current location of a unit, just select the appropriate IP address and the current position of the selected unit will be used as origin point.
• Set the X-axis angle, that is, the angle relative to due North. For example, leaving this at 0 will set the X-axis to point North, and the Y-axis to point West. In the picture below, the angle is set to 90 degrees, meaning that the X-axis will point East and the Y-axis will point North.

• Click OK and commit the new configuration. This will save the local coordinates setting to the unit’s memory, and the setting will remain available even if the unit is switched off.

 

Setting local coordinates in NAVdisplay:

• Power the unit and connect to it.
• Open NAVdisplay. Select the unit you wish to set the local coordinates on.
• Open the "Utilities" menu and select "Quick config". The following window will open up:

• Select the appropriate unit and click on Local coordinates. The following window will open up:

• If the unit has initialised, you can select the current position of the selected unit to be the origin point of the coordinates system by clicking on "Set origin".
• Click on "Set axis": the system will require you to drive 100 metres away from the origin to establish the X-axis. This will be set between the origin point and the point where you first reach 100 metres distance from it.
• The local coordinates system will be immediately operative, with no need to reboot the unit, but it will NOT be saved when the unit is reset. If you wish to save the settings, the appropriate box must be ticked BEFORE setting the origin and the X-axis.

 

3) Use of local coordinates with RT-Range systems

A local coordinates grid can be set on a RT-Range system as well, following this procedure:

• Power the RT-Range box and connect to it.
• Open Real-time display in RT-Range software and select Configure RT-Range
• Navigate to the "Options" page and select "Local Coordinates"

• The following window will open up:

• Enable the local coordinates, then type in the origin point values. You can use the current location of a unit, just select the appropriate IP address and the current position of the selected unit will be used as origin point.
• Set the X-axis angle, that is, the angle relative to due North. For example, leaving this at 0 will set the X-axis to point North, and the Y-axis to point West.
• Click next and commit the new configuration. This will save the local coordinates setting to the RT-Range box memory, and the setting will remain available even if the RT-Range is switched off.

 

Multiple local coordinates systems

In a RT-Range system, depending on what data is required in local coordinates, local grids can be set on the RT-Range only, or on any number of RT units (hunter and targets) as well. Each of the RTs and the RT-Range will calculate local coordinates values based on the local coordinates system configured within that unit.

Therefore, output from the RT-Range (Hunter and Target relative positions, velocities, etc.) will be in the local coordinates system defined in the RT-Range, whereas output from the RTs (even the data from the RTs that is carried in the RCOM stream), such as position and velocity, will be in the local coordinates system defined in the respective RT.

While all these local coordinates systems can be set to be different, it is recommended to use exactly the same system on all the RT units and the RT-range involved in the testing, to avoid confusion.

 

Local reference system and hunter reference system

All the range relative measurements are always reported in the Hunter reference system, where the RT unit designed as hunter is the “zero point” for all range measurements.

When using a local coordinates system for RT-Range measurements, it is important not to confuse the two reference systems:

The local coordinates reference system is fixed: origin and axes do NOT move or rotate.

The hunter reference system is variable: the origin moves and the axes rotates according to the hunter movements.

 

 

4) Local coordinates in post-processing

Even when no local coordinates were set before a testing session, data can still be post-processed referring the collected data to a local coordinates system, following this procedure:

• Open the RD file in RT Post-Process
• Navigate to the Process page and click Review Configuration

• NAVconfig will open up. Go to the Options page
• Select Local coordinates
• Enter the lat/lon/alt coordinates of the origin you want to use and the X-axis angle, in the usual way.
• Click OK, then "Next" on the "Options" Page, then "Finish" on the next page. Post-process the file, and the local coordinates data will be available.

The same could be done when post-processing RT-Range data, setting a local coordinates system in the apposite "Options" page of the RT-Range software\Post Processing wizard:

 

5) How is local coordinates data calculated

The local coordinates frame is a flat plane that can be considered accurate enough when it comprises a small area. Over very large areas, XY position errors will be increasingly affecting measurement values, because the surface of the Earth is curved.

Applying local coordinates effectively creates another layer of processing on top of the core one that generates the standard outputs seen in the NCOM stream. This additional process compares all the standard position/velocity measurements to the reference point selected as origin point, to create the local coordinates counterparts.

Any setting that affects the standard output data set will be reflected in the local coordinates data set as well.