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Chapter 5:
The functions in this grouping set or query parameter values, parameter information,
and parameter constraints that characterize hardware. A parameter is a hardware
setting. Parameters have varying qualities as well as values and constraints. A parameter
may have several different values but constraints determine which kinds of values a
parameter can have based on hardware type, read/write capability, or other parameters
used or to be used in describing and setting up specific hardware. If a camera has been
opened, it can be configured by changing its parameters through software and applying
them to the hardware. If an accessory has been opened, it can be configured directly.
Each different hardware model has a different set of parameters. Parameters contain
different attributes.
The most important parameter attribute is its value. Values are represented by different
types (i.e., integer, floating point, enumeration, etc.)
All parameter values can be read, but not all can be written. This is determined by the
parameter's value access:
Parameter values that can be written have constraints. Constraints describe the set of
values a parameter value can take. The nature of this set determines the constraint type
(e.g., a numeric range, a set of options, etc.) It is useful to describe a different constraint
based on purpose. This is where constraint categories come into play. These categories
differentiate "Is this parameter capable of x?" from "Based on the current configuration,
is it valid to set parameter to x?"
Due to the complex nature of configuration, some parameters override others when
certain values are set. A parameter is relevant if it has an effect on the current
configuration.
For a camera, most parameters are only used for acquisition setup. However, this is not
always the case. Some parameters can be modified while the hardware is acquiring.
These parameters are deemed onlineable. Note that accessories are not onlineable
since they do not acquire data.
Still other parameters reflect the current state of the hardware. These parameters only
have meaning when read directly from hardware and are termed readable.
Another parameter may reflect the status of hardware that is not directly controllable
by the software (e.g., may be changed due to external influences,) yet it's value may
impact the decisions and/or further progress of the software. Such a parameter is a
waitable status.
For a camera, once the parameter values have been adjusted as desired they must be
committed to the hardware before the hardware can be used.
Configuration APIs
•
Read/Write
•
Read Only.
NOTE:
A special case of value access is when a parameter value can
be written, but only one particular value is permitted. This is
called read/write trivial.
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