Observations and Point Group Requirements for USMN

When setting up a network for analysis with USMN, there are several organizational requirements for instruments, measurements, point groups, and point names. The requirements for USMN analysis are as follows:

Point Naming and Observation Requirements:

As with any measurement network, common targets must be measured by more than one instrument to form a network, therefore:

  1. Individual point names must be common between groups as USMN will associate measurements from different instruments based on point names.

  2. Points in different groups with the same name must represent the same target. For example, MeasStation1::P1, MeasStation2::P1, … MeasStationN::P1 will be combined to compute the composite point P1.

Points without measurements are ignored, unless the point group is included as a ‘Nominal Group.’ Therefore:

  1. A specific point in a given point group should have observations from only one instrument.

An instrument can make more than one measurement to a specific point. As an example, an instrument can have a front and back sight to a point or an instrument might have N front sight measurements to a point. Observations that are marked as ‘ignored’ are not included in the USMN network. The measurement details dialog for a point provides an interface to determine whether or not an observation is ignored.

Consider an example tree for a job ready for a USMN network as seen in the following:

 

To help identify potential problems with point names, a warning dialog will display showing the Network Build point and instrument listing. This dialog helps to identify any potential problems when you first start the USMN process. You may see something line the following:

 

In the above dialog point groups are marked in red or blue to provide a warning that a user may want to exclude them.

The primary output from USMN is a Composite Point Group. This group contains the optimal point coordinates (the most likely position of the points) after solving the network. Inputs to USMN include both the instruments and their measurements. For a measurement to affect the calculation, it must have been measured from multiple instrument stations. The observations from different stations are made into different point groups, but should have the same target name.