STAR*NET V6 - Circe

Chapter 10 Adjustments in Grid Coordinate Systems
10.2 How STAR*NET Works with Grid Systems
STAR*NET adjusts your surveyed observations “on-the-plane.” What this means is that,
using the projection formulas for the selected grid system and ellipsoid, and the entered
geoid height, STAR*NET takes the surveyed data measured at earth-surface level and
fits it all together on the grid plane during an adjustment. Handling the adjustment in this
fashion provides one consistent rectangular system to combine different types of
observations in an understandable way. These types of observations include: surveyed
surface observations reduced by the program, entered measurements already on the grid
plane (for example, entered grid bearings, or grid distances from maps), and GPS vectors
rotated to north, east and up vector components on the specified grid plane. Handling of
GPS vectors is supported in the STAR*NET Professional Edition.
However, what this also means is that, since grid adjustments use the actual grid plane
during the adjustment process, the size of your project is restricted to the approximate
extent of the grid system boundary so that geodetic-to-grid formulas remain accurate.
STAR*NET is designed for typical survey grid projects in relatively small areas
spanning up to a few hundred kilometers, the extent of a typical grid system. The
program cannot be used to adjust survey observations in a single project that spans
thousands of kilometers or miles, covering multiple grid zones.
10.3 Units of Length
STAR*NET allows you to select different length units: US Survey Foot, International
Foot, and Meter are built into the program and the user may define additional units of
length in the Custom file, “STAR6.CUS” described later in this chapter. The US Survey
Foot is defined as 1200/3937 of a meter, and the International Foot as 0.3048 meter,
which is shorter by about 2 PPM.
It is up to you to make sure that your project is using the proper units for your particular
known control coordinates. For example, official NAD27 coordinates are given in US
Survey Feet, and NAD83 in either Meters or US Survey Feet. However, there are some
NAD83 zones that were originally defined using International Feet!
10.4 Signs of Geodetic Positions
The sign convention for Longitudes is set as a preference in the Project Options/General
dialog settings. The use of “positive” west longitudes (those west of Greenwich) is
preferred by most users in the USA and Canada; “negative” west longitudes by the
international community. Whichever convention preference you select for a project, it
will be used for all grid systems supported: NAD27/83, UTM and Custom. Note that if
you consistently use one sign convention for all projects, be sure to set that preference in
your company options so that all new projects will be defaulted to that convention.
The sign convention for Latitudes is always positive to the north of the equator, and
negative to the south.
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