Populate classId and confidence level for object detection in Java simulation (#2372)

## Description

compute confidence level based on target area in total image size and
populate classId and confidence level in Java (while building the
PhotonTrackedTarget)

## Changes
- Add new VisionTargetSim constructor for object detection
- If class ID specified but confidence = -1, estimate based on total
area

---------

Co-authored-by: Matt Morley <matthew.morley.ca@gmail.com>

photon-lib/src/main/java/org/photonvision/simulation/PhotonCameraSim.java

@@ -525,6 +525,16 @@ public class PhotonCameraSim implements AutoCloseable {
                                 .get();
             }
 
+            // If object detection (user classId valid) but conf wasn't provided, estimate
+            int classId = tgt.objDetClassId;
+            float conf = tgt.objDetConf;
+            if (classId >= 0 && conf < 0) {
+                // Simulate confidence using sqrt-scaled area for a more realistic
+                // curve. Raw areaPercent/100 is tiny for most targets; sqrt scaling
+                // gives reasonable values even for small-but-visible objects.
+                conf = (float) MathUtil.clamp(Math.sqrt(areaPercent / 100.0) * 2.0, 0.0, 1.0);
+            }
+
             detectableTgts.add(
                     new PhotonTrackedTarget(
                             -Math.toDegrees(centerRot.getZ()),
@@ -532,8 +542,8 @@ public class PhotonCameraSim implements AutoCloseable {
                             areaPercent,
                             Math.toDegrees(centerRot.getX()),
                             tgt.fiducialID,
-                            -1,
-                            -1,
+                            classId,
+                            conf,
                             pnpSim.best,
                             pnpSim.alt,
                             pnpSim.ambiguity,

photon-lib/src/main/java/org/photonvision/simulation/VisionTargetSim.java

@@ -36,16 +36,21 @@ public class VisionTargetSim {
 
     public final int fiducialID;
 
+    /** The object detection class ID, or -1 if not applicable. */
+    public final int objDetClassId;
+
+    /** The object detection confidence, or -1 if not applicable. */
+    public final float objDetConf;
+
     /**
-     * Describes a vision target located somewhere on the field that your vision system can detect.
+     * Describes a retro-reflective/colored shape vision target located somewhere on the field that
+     * your vision system can detect.
      *
      * @param pose Pose3d of the tag in field-relative coordinates
      * @param model TargetModel which describes the geometry of the target
      */
     public VisionTargetSim(Pose3d pose, TargetModel model) {
-        this.pose = pose;
-        this.model = model;
-        this.fiducialID = -1;
+        this(pose, model, -1, -1, -1);
     }
 
     /**
@@ -56,9 +61,33 @@ public class VisionTargetSim {
      * @param id The ID of this fiducial tag
      */
     public VisionTargetSim(Pose3d pose, TargetModel model, int id) {
+        this(pose, model, id, -1, -1);
+    }
+
+    /**
+     * Describes an object-detection vision target located somewhere on the field that your vision
+     * system can detect. Class ID is the (zero-indexed) index of the object's class ID in the list of
+     * all classes. Confidence can be specified, or pass -1 to estimate confidence based on 2 *
+     * sqrt(target area / total image area)
+     *
+     * @param pose Pose3d of the target in field-relative coordinates
+     * @param model TargetModel which describes the geometry of the target
+     * @param objDetClassId The object detection class ID, if -1 it will not be detected by object
+     *     detection
+     * @param objDetConf The object detection confidence, or -1 in which case the simulation will
+     *     compute a confidence based on the area of the target in the camera's field of view
+     */
+    public VisionTargetSim(Pose3d pose, TargetModel model, int objDetClassId, float objDetConf) {
+        this(pose, model, -1, objDetClassId, objDetConf);
+    }
+
+    private VisionTargetSim(
+            Pose3d pose, TargetModel model, int id, int objDetClassId, float objDetConf) {
         this.pose = pose;
         this.model = model;
         this.fiducialID = id;
+        this.objDetClassId = objDetClassId;
+        this.objDetConf = objDetConf;
     }
 
     /**
@@ -97,7 +126,11 @@ public class VisionTargetSim {
         return model;
     }
 
-    /** This target's vertices offset from its field pose. */
+    /**
+     * This target's vertices offset from its field pose.
+     *
+     * @return A vector of Translation3d representing the vertices of the target
+     */
     public List<Translation3d> getFieldVertices() {
         return model.getFieldVertices(pose);
     }