When dealing with the Total Station, you will often encounter surveying terms that need clarification.
The most important ones are:
- Job – the data collector “project” or “document” is a job. Use a different job for each location or when re-surveying a stage.
- Occupy Point – physical point where the total station is setup.
When starting a new Job, the first point will often be your Occupy Point as well as your Origin (Northing = 0.000m, Easting = 0.000m and Elevation = 0.000m).
- Instrument Height – physical height of the Total Station instrument (measured in meters) from floor to optical witness mark (often on laser pivot), indicated by a dot.
- Backsight – point that determines heading in a survey. When setting up a new survey, you will need to elect a heading for the Northing (X-axis). This is based on an Azimuth projection where every point is calculated in an angle derived from the position of this axis.The height of the backsight is negligible, it can be on the ceiling, the walls, the floor or any reference. The one request is that the backsight point be set somewhat perpendicular to the green screen or cyclorama.This makes it easier to reference and make changes in real-time in Previzion.
- Traverse – when moving the total station to a known point, you traverse to this point after measuring it.
- Resection – when entering a survey space with a few known points, you may create a new occupy point based on a re-measurements of known points.
- Point Description – to identify a point, each point gets a description. This is often the number of the fiducial target or OP for occupy point, BP for backsight point and RS/RP for resection point.
The origin is the location on the survey where Northing, Easting and Elevation all equal 0.000 meters. From this point all measurements are taken from.
To simplify the process, the first point (occupy point) is defined as the origin. The origin should be in a central location with respect to the action of the scene or stage. Exact centering isn’t necessary.
There are many Total Stations and various brands. The two key features needed to survey without using a professional surveyor are:
- Reflectorless Mode – this allows the total station to take measurements without the use of a prism or reflective stickers.
- Data Collector – this is a separate piece of hardware that acts like a handheld computer. The Data Collector is able to store and output point data as well as configure the total station.
- Bluetooth Data or Serial Data Cable for Data Collector – for the Data Collector to communicate with the Total Station, you will need either bluetooth connectivity or a hard wired serial cable connection. We recommend having a cable as bluetooth often drops out in sound stages.
Using a data collector is particularly handy because it allows for a graphical interface and the ability to quickly access and edit points as needed.
Types of Points to Survey
There are four different types of points to survey, and each plays a different role in aligning together the physical and virtual worlds. Using the measurements from the total station, you can extend and reference real sets with virtual elements.
The four types of surveyed points are:
- Backsight / Origin (red) – used for setting up the total station
- Fiducial Targets (orange) – used by the IS1200 for tracking
- Garbage Mattes (yellow) – (optional) can be used by Previzion to matte out areas where the green screen ends
- Stage Props and References (cyan) – (optional) can be used to create CG scenes with elements that line up with real elements.
Once you’ve surveyed, you’ll need to convert the survey data to X, Y, Z coordinates. This can be done using Constellation Tool, available for download from Dashboard.