Arc sine (inverse sine): asin

The asin template function returns the arc sine (inverse sine) of a value. The result is in radians, in the range [-pi/2, pi/2]. The input must be between -1 and 1.

This is useful when you need to convert a ratio back into an angle. For example, given a normalized sensorSensors return information about a thing, for instance the level of water in a tank. [Learn more] reading you could recover the original angle used to produce it.

Usage

Here’s how to use this template function. Copy any example and adjust it to your setup.

{{ asin(1) }}

1.5707963267948966

{{ 1 | asin }}

1.5707963267948966

Function signature

The signature is a technical summary of this template function. It shows the name of the function, the values (called parameters) it accepts, and what type of data each parameter expects (for example, a piece of text or a number).

Function parameters that have a = with a value after them are optional. If you leave them out, the default value shown is used automatically. Function parameters without a default are required.

asin(
    value: Any,
    default: Any = None,
) -> float

Function parameters

The following parameters can be provided to this function.

Good to know

• Inputs outside the range -1 to 1 raise an error unless you supply a default.
• The result is in radians. Multiply by 180 / pi to convert to degrees.

Try it yourself

Ready to test this? Open Developer tools > Template, paste the example into the Template editor, and watch the result update on the right. Edit the values to see how the function adapts to your own entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this function comes up in automations and templates. Copy any example and adapt it to your setup.

Using a default value

If the input might be out of range or non-numeric, provide a default to avoid errors. This keeps your templateA template is an automation definition that can include variables for the action or data from the trigger values. This allows automations to generate dynamic actions. [Learn more] from breaking when a sensorSensors return information about a thing, for instance the level of water in a tank. [Learn more] is temporarily unavailable.

{{ asin(states("sensor.ratio"), default=0) }}

0

Convert arc sine to degrees

Convert the result from radians to degrees to make it more readable.

{{ (asin(0.5) * 180 / pi) | round(1) }}

30.0

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with your template and expected result, or share on our subreddit /r/homeassistant.

Related template functions

These functions work well alongside this one:

• Sine: sin - Returns the sine of a value given in radians.

• Arc cosine (inverse cosine): acos - Returns the arc cosine (inverse cosine) of a value, in radians.

• Arc tangent (inverse tangent): atan - Returns the arc tangent (inverse tangent) of a value, in radians.

• Four-quadrant arc tangent: atan2 - Returns the four-quadrant arc tangent of y/x, in radians.