Skip to content

Posital

Overview

Posital devices reads an absolute rotary/position encoder over the network. Onlyview opens a TCP connection to the encoder and receives its position continuously, so the show always knows where a physical axis is. It can either be the live angle of a revolving stage, or the position of a moving truss, wagon or set piece.

The raw count coming from the encoder is converted into a usable value (degrees, metres, or whatever unit suits the show) using a scale factor and an offset that you need to tune using the built-in calibration. The show reads that converted value through the Posital ActionGraph node.

Info

The TCP port used to reach the encoder is fixed at 6000 and cannot be changed. Only the address of the encoder is configurable.

Setup

  • Name: A descriptive name for the device, used wherever it appears in the interface.
  • Ip Adress: The IP address of the encoder on the network.
  • Filter (against lag): A group box you can tick or untick to enable the anti-lag filter, with the filter time in milliseconds inside it. See below.
  • Calibration: The two conversion parameters.
    • Offset: The value added after scaling.
    • Coeff: The scale factor applied to the raw encoder count.
    • Calibrate ...: Opens the calibration dialog described in the next section.

Coeff and Offset

Onlyview converts the raw encoder reading into the output value with a simple linear formula:

output = raw reading × Coeff + Offset**

Coeff sets the unit — how much one encoder count is worth in the unit you want to work in, and Offset sets the origin: it is the output value you get when the encoder reads zero.

The filter

A value read over the network is always slightly old by the time the show uses it, and a fast-moving axis has moved on in the meantime. When Filter (against lag) is enabled, Onlyview estimates the speed of the axis and extrapolates the position forward by the filter time you give, then applies Coeff and Offset, so the value stops trailing behind a moving axis.

The trade-off is that extrapolation is a guess: it is only correct while the speed stays constant, so it overshoots at the start and the end of a move, and it amplifies any jitter in the readings — the longer the filter time, the more of both.

Calibration

You can type Coeff and Offset in by hand, but it is normally easier to guess them using two known positions of the machine. Click Calibrate ... in the setup dialog to open the Posital calibration dialog.

  1. Check that the device is connected: the Real codeur value display at the top shows the live raw count and should react when the machine moves.
  2. In the In Position group, type the value you want the device to output at your first reference position into Output value at the In point — for example 0 for the centre line of a revolving stage.
  3. Move the machine to that position, then click Set In. The raw count is captured and shown next to the button.
  4. In the Out Position group, type the value expected at your second reference position into Output value at the Out point — for example 90 for a quarter turn.
  5. Move the machine to that second position and click Set Out.
  6. Offset and Coeff at the bottom of the dialog are now filled in, and the OUT field shows the resulting output value live. Move the machine around and check the numbers at positions you know.
  7. Click OK to carry the two values back into the setup dialog, then OK again to apply them. Cancel in either dialog leaves the existing calibration untouched.

Pick the two reference positions as far apart as the machine allows: the further apart they are, the less an error in reading them affects the scale factor.

Warning

Typing a new value into Output value at the In point or Output value at the Out point does not recompute anything on its own. If you change either one after capturing a point, click the matching Set In or Set Out button again, with the machine back at that position, to recalculate.

ActionGraph Nodes

Posital

Reads the calibrated value of a Posital device. Available under Devices/Posital in the node palette.

Properties:

  • Device: The Posital device to read.

Output Slots:

  • Position: Float — the calibrated value, that is the raw encoder reading converted through the filter, Coeff and Offset.

The output is invalid while the device is not connected, or if the selected device no longer exists.

Device Widget

The Posital device widget can be placed on a UserScreen. It shows the connection status, the Real Codeur Value (the raw count, useful when checking a calibration) and the OUT value the show actually uses. Connect and Disconnect buttons let an operator drop and re-establish the connection; both also exist as device actions, so they can be triggered from a timeline or a cuelist.

For another device bringing physical sensors and encoders into ActionGraph, see Phidget.