add camera_info input for the pinhole model

Nothing in a dataflow carries fx, fy, cx and cy except the camera, and every
pixel of a depth map needs them to become a 3D point. The node now accepts
them so whatever computes that next has them to hand.

They are read from two places because dora-zed publishes them twice: the
camera_info message, and the metadata of every frame. The per-frame copy is
not redundant -- camera_info goes out once per camera session, so a viewer
started after the camera would otherwise never see it, and reading frame
metadata means wiring the input is optional even for a camera that publishes
it.

A nine-element row-major K is accepted alongside the compact [fx, fy, cx, cy],
since that is how ROS spells the same model in sensor_msgs/CameraInfo.

The model is drawn under the caption rather than only stored. A depth map read
through the wrong intrinsics looks entirely plausible, and this is where that
becomes visible.

as_float32 moves to a payload module: camera_info arrives as a raw byte slice
for the same reason the depth map does, and the reinterpretation is now shared
rather than written twice.

Verified with dora-cli 1.0.1: validate passes with four contracts injected on
each side, the dataflow runs to a clean exit, and a composed frame was
rendered and inspected with the model drawn on it.

examples/dora-node.yml

@@ -12,7 +12,7 @@
 apiVersion: 1
 name: source
 namespace: liria
-description: Synthetic image, depth, bbox and text source for the dora-image-view example
+description: Synthetic image, depth, camera_info, bbox and text source for the dora-image-view example
 categories: [debug]
 keywords: [example, test, synthetic]
 
@@ -39,6 +39,11 @@ outputs:
   text:
     type: std/core/v1/String
     description: A fixed caption.
+  camera_info:
+    type: std/core/v1/Float32
+    description: >-
+      [fx, fy, cx, cy] for the frames above. Published once, on the first tick,
+      the way a real camera publishes it once per session.
   depth:
     type: std/core/v1/Float32
     description: >-

examples/source.py

@@ -5,7 +5,9 @@ moving in it, and a caption -- every input dora-image-view draws -- so the examp
 dataflow needs no camera, no detector and no network.
 
 The depth map describes the same scene as the image: a flat back wall with the square
-standing in front of it.
+standing in front of it. `camera_info` is published once, on the first tick, the way a
+real camera publishes it once per session -- which is exactly the case the viewer has
+to cope with by reading intrinsics from frame metadata as well.
 """
 
 import os
@@ -27,9 +29,17 @@ CAPTION = "dora-image-view synthetic source"
 WALL_MM = 2000.0
 SQUARE_MM = 800.0
 
+# A plausible pinhole for a frame this size.
+FX = FY = float(WIDTH)
+CX, CY = WIDTH / 2, HEIGHT / 2
+DISTORTION = [0.0, 0.0, 0.0, 0.0, 0.0]
+# Attached to every frame as well as published once, which is what dora-zed does
+# and what lets a viewer that started late still learn the camera model.
+INTRINSICS_METADATA = {"fx": FX, "fy": FY, "cx": CX, "cy": CY, "distortion": DISTORTION}
+
 
 def main() -> None:
-    """Send one image, depth map, bbox and text per tick."""
+    """Send one image, depth map, bbox and text per tick, and camera_info once."""
     node = Node("source")
     sent = 0
 
@@ -37,11 +47,18 @@ def main() -> None:
         if event["type"] != "INPUT":
             continue
 
+        if sent == 0:
+            node.send_output(
+                "camera_info",
+                pa.array(np.array([FX, FY, CX, CY], dtype=np.float32)),
+                {"shape": [4], "dtype": "float32", "layout": "C", "distortion": DISTORTION},
+            )
+
         frame, corners = render(sent)
         node.send_output(
             "image",
             pa.array(frame.ravel()),
-            {"width": WIDTH, "height": HEIGHT, "encoding": "bgr8"},
+            {"width": WIDTH, "height": HEIGHT, "encoding": "bgr8", **INTRINSICS_METADATA},
         )
         node.send_output(
             "bbox",
@@ -56,7 +73,13 @@ def main() -> None:
         node.send_output(
             "depth",
             pa.array(depth.ravel()),
-            {"shape": [HEIGHT, WIDTH], "dtype": "float32", "layout": "HW", "units": "mm"},
+            {
+                "shape": [HEIGHT, WIDTH],
+                "dtype": "float32",
+                "layout": "HW",
+                "units": "mm",
+                **INTRINSICS_METADATA,
+            },
         )
         node.send_output("text", pa.array([CAPTION]))