Remove support for custom unobserved values

### What change is being made

Removes the deprecated `unobserved_value` field from spherical range image metadata.

### Why this change is being made

All image APIs now use `NaN` to represent unobserved pixels. For details, see the [Camera and LiDAR Conventions](https://app.notion.com/p/theaiinstitute/Camera-and-LiDAR-conventions-32ced28d384980f6a9e8f32030ba275d) in Notion.

The metadata field is therefore no longer needed. Removing it avoids ambiguity and also avoids having to represent and parse `NaN` floating-point values in JSON, which is not natively supported by the [nlohmann/json](https://github.com/nlohmann/json) library.

### Tested

Tested in MuJoCo with:

* A modern navigation policy using `NaN` for unobserved pixels
* Legacy policies using `-1` for unobserved pixels

Legacy policy compatibility is temporarily provided by control [PR #4332](https://github.com/rai-inst/control/pull/4332) to support the transition.

GitOrigin-RevId: e4ab29ddfb800de6c929b9767bc328c73d15ba17

Author: vreijgwart-bdai

control/include/exploy/metadata.hpp

@@ -158,16 +158,14 @@ inline void from_json(const json& j, HeightScanMetadata& hs) {
 /**
  * @brief Metadata for spherical image sensors (e.g., LiDAR).
  *
- * Specifies the configuration for spherical images including resolution, field of view,
- * and sentinel value for unobserved points.
+ * Specifies the configuration for spherical images including resolution and field of view.
  */
 struct SphericalImageMetadata {
   std::string pattern_type{};  ///< Spherical image pattern type.
   int v_res{};                 ///< Vertical resolution (number of vertical scan lines).
   int h_res{};                 ///< Horizontal resolution (points per scan line).
   double v_fov_min_deg{};      ///< Minimum vertical field of view in degrees.
   double v_fov_max_deg{};      ///< Maximum vertical field of view in degrees.
-  double unobserved_value{};   ///< Sentinel value for unobserved/invalid points.
 };
 
 /**
@@ -182,7 +180,6 @@ inline void from_json(const json& j, SphericalImageMetadata& si) {
   j.at("h_res").get_to(si.h_res);
   j.at("v_fov_min_deg").get_to(si.v_fov_min_deg);
   j.at("v_fov_max_deg").get_to(si.v_fov_max_deg);
-  j.at("unobserved_value").get_to(si.unobserved_value);
 }
 
 /**

control/include/exploy/state_interface.hpp

@@ -172,12 +172,11 @@ struct HeightScanInfo {
 /// @brief Arguments for RobotStateInterface::initSphericalImage and
 ///        RobotStateInterface::sphericalImage.
 struct SphericalImageInfo {
-  std::string sensor_name;    ///< Name of the spherical image sensor.
-  int v_res{};                ///< Number of pixels in vertical direction (used by init).
-  int h_res{};                ///< Number of pixels in horizontal direction (used by init).
-  double v_fov_min_deg{};     ///< Minimum vertical field of view angle in degrees (used by init).
-  double v_fov_max_deg{};     ///< Maximum vertical field of view angle in degrees (used by init).
-  double unobserved_value{};  ///< Sentinel value for pixels with no sensor return (used by init).
+  std::string sensor_name;  ///< Name of the spherical image sensor.
+  int v_res{};              ///< Number of pixels in vertical direction (used by init).
+  int h_res{};              ///< Number of pixels in horizontal direction (used by init).
+  double v_fov_min_deg{};   ///< Minimum vertical field of view angle in degrees (used by init).
+  double v_fov_max_deg{};   ///< Maximum vertical field of view angle in degrees (used by init).
   std::unordered_set<std::string> channel_names{};  ///< Channel names to include / retrieve.
 };
 

control/src/components.cpp

@@ -424,7 +424,6 @@ SphericalImageInput::SphericalImageInput(const std::string& key, const std::stri
           .h_res = static_cast<int>(metadata.h_res),
           .v_fov_min_deg = metadata.v_fov_min_deg,
           .v_fov_max_deg = metadata.v_fov_max_deg,
-          .unobserved_value = metadata.unobserved_value,
           .channel_names = channel_names,
       } {}
 

control/test/testdata/test_onnx_generator.py

@@ -182,7 +182,6 @@ def get_sensor_metadata() -> dict:
             "h_res": 1024,
             "v_fov_min_deg": -45.0,
             "v_fov_max_deg": 45.0,
-            "unobserved_value": -2.0,
         },
         "sensor.pinhole_image.one": {
             "pattern_type": "grid_pattern",