Value Scaling Function

float scale(float value, float minA, float maxA, float minB, float maxB)
{
    // compute scaling factor:
    float rangeA = maxA - minA;            // dx
    float rangeB = maxB - minB;            // dy
    float slope = rangeB / rangeA;         // m
    float intercept = minB - slope * minA; // b

    // compute value in new range:
    float result = value * slope + intercept; // f(x)=m*x+b

    // cut the new value if it is out of bounds:
    if(result > maxB) result = maxB;
    if(result < minB) result = minB;

    return result;
}

This rather simple function linearly scales a value within range [minA, maxA] to a new range [minB, maxB].

Application Example

Let's say you want to have sensor readings within range [0°, 180°] of a laser scanner, but you want to store the data within the range [-1,1] because you let the laser scan a 180° field and 90° means straight ahead; you want that direction to be at 0. So you just call

scale(value, 0, 180, -1, 1) for an incomming sensor reading value and get the scaled one.

Inline Version

float scale(float value, float minA, float maxA, float minB, float maxB)
{
    // compute value in new range and cut if out of bounds:
    float slope = (maxB - minB) / (maxA - minA);
    float v = value * slope + minB - slope * minA;
    return v > maxB ? maxB : (v < minB ? minB : v);
}