UKismetMathLibrary::Asin

function Engine Blueprint Since 4.0

#include "Kismet/KismetMathLibrary.h"

Access: public Specifiers: staticUFUNCTIONBlueprintPure

Description

Returns the inverse sine (arcsine) of A in radians. The result is in the range [-PI/2, PI/2].

Caveats & Gotchas

• If A is outside [-1, 1], the result is NaN per IEEE 754 — the engine does not clamp or assert. Always validate the input if it comes from a calculation that might slightly exceed 1.0 due to floating-point error (e.g., dot products of nearly-parallel unit vectors).
• The result is in radians in the range [-PI/2, PI/2] (i.e., [-90°, 90°]) — it cannot recover angles outside that range because sine is not injective outside it. Use Atan2 if you need a full 360° inverse.

Signature

static UE_INL_API double Asin(double A);

Parameters

Name	Type	Description	Default
A	double	The sine value, must be in the range [-1, 1].	—

Return Type

double

Example

Recover a launch angle from a known vertical-to-speed ratio C++

double VerticalSpeed = LaunchVelocity.Z;
double TotalSpeed = LaunchVelocity.Size();
if (TotalSpeed > KINDA_SMALL_NUMBER)
{
    double SinAngle = FMath::Clamp(VerticalSpeed / TotalSpeed, -1.0, 1.0);
    double AngleRadians = UKismetMathLibrary::Asin(SinAngle);
    double AngleDegrees = FMath::RadiansToDegrees(AngleRadians);
}

Version History

Introduced in: 4.0

Version	Status	Notes
5.6	stable	—

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