The main key concept in INDI is that devices have the ability to describe themselves. This is accomplished by using XML to describe a generic hierarchy that can represent both canonical and non-canonical devices. In INDI, all devices may contain one or more properties. Any property may contain one or more elements. There are four types of INDI properties:
Switch property (Represented in GUI by buttons and checkboxes).
Light property (Represented in GUI by colored LEDs).
For example, all INDI devices share the CONNECTION standard switch property. The CONNECTION property has two elements: CONNECT and DISCONNECT switches. KStars parses the generic XML description of properties and builds a GUI representation suitable for direct human interaction.
The INDI control panel offers many device properties not accessible from the sky map. The properties offered differ from one device to another. Nevertheless, all properties share common features that constrains how they are displayed and used:
Permission: All properties can either be read-only, write-only, or read and write enabled. An example of a read-write property is the telescope's Right Ascension. You can enter a new Right Ascension and the telescope, based on current settings, will either slew or sync to the new input. Furthermore, when the telescope slews, its Right Ascension gets updated and sent back to the client.
State: Prefixed to each property is a state indicator (round LED). Each property has a state and an associated color code:
Table 7.1. INDI State color code
State Color Description Idle Gray Device is performing no action with respect to this property Ok Green Last operation performed on this property was successful and active Busy Yellow The property is performing an action Alert Red The property is in critical condition and needs immediate attention
The device driver updates the property state in real-time when necessary. For example, if the telescope is in the process of slewing to a target, then the RA/DEC properties will be signaled as Busy. When the slew process is completed successfully, the properties will be signaled as Ok.
Context: Numerical properties can accept and process numbers in two formats: decimal and sexagesimal. The sexagesimal format is convenient when expressing time or equatorial/geographical coordinates. You can use any format at your convenience. For example, all the following numbers are equal:
Time: The standard time for all INDI-related communications is Universal Time UTC specified as YYYY-MM-DDTHH:MM:SS in accord with ISO 8601. KStars communicates the correct UTC time with device drivers automatically. You can enable/disable automatic time updates from the page in the settings dialog.