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Clarify min and max temperature of thermal camera #523

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iche033 merged 1 commit into from
May 14, 2025
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Clarify min and max temperature of thermal camera #523

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17 changes: 12 additions & 5 deletions tutorials/thermal_camera.md
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Expand Up @@ -114,13 +114,20 @@ As we can see, we define a sensor with the following SDF elements:

There's also an optional plugin used here that allows for further configuration of the thermal camera.
Here's a description of the elements in this plugin (if the plugin isn't used, the default values mentioned below are used):
* `<min_temp>`: The thermal camera's minimum temperature, in Kelvin.
The default minimum temperature is `0`.
* `<max_temp>`: The thermal camera's maximum temperature, in Kelvin.
The default maximum temperature is calculated as `(2^(bitDepth) - 1) * resolution`.
For a 8-bit thermal camera with a linear resolution of `3.0`, the maximum temperature is `((2^8) - 1) * 3 = 765 Kelvin`.
* `<resolution>`: The thermal camera's linear resolution.
This defines the mapping of temperatures onto image values.
A temperature of `x` Kelvin corresponds to an image value of `x * resolution`.
Note that this implies an implicit minimum temperature of `0` Kelvin and an implicit maximum temperature of `(2^bitDepth - 1) * resolution` Kelvin due to the limited range of image values.
For example, for an 8-bit thermal camera with a linear resolution of `3.0`, the implicit maximum temperature is `((2^8) - 1) * 3 = 765 Kelvin`.
The default linear resolution is `0.01` for a 16-bit thermal camera, and `3.0` for a 8-bit thermal camera.
* `<min_temp>`: The thermal camera's additional minimum temperature, in Kelvin.
By default, there is no additional lower bound.
* `<max_temp>`: The thermal camera's additional maximum temperature, in Kelvin.
By default, there is no additional upper bound.

Note that the elements `<min_temp>` and `<max_temp>` do not influence the mapping between image values and temperatures.
Instead, they are only used for clamping down the camera output:
Any temperature lower than `<min_temp>` will be output by the camera as if it was *exactly equal* to `<min_temp>` (and symmetrically for `<max_temp>`).

## Assigning a temperature to a model

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