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fix frame timestamps to use a comparable epoch

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steady_clock's epoch is unspecified and typically counts from process start or
boot, so the published timestamp_ns could not be compared against another
node's timestamps, wall clock or a recording — and it recorded when the node
processed the frame rather than when the camera captured it.

Publish two keys on every output instead: device_timestamp_ns from
sl::Camera::getTimestamp(TIME_REFERENCE::IMAGE), and host_timestamp_ns from
system_clock. Both are Unix-epoch nanoseconds, set as dora timestamp
parameters. The SDK clock source is pinned to SYSTEM_CLOCK at construction,
since it is process-wide and decides the epoch of the device value.

Both are kept because the wall clock can step when NTP synchronises after boot
on a Jetson, while the device timestamp is what two nodes reading the same
frame can agree on.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7g2cBJ5e3r15ZbJ9WZn8c
This commit is contained in:
cesar
2026-09-08 09:15:47 -03:00
co-authored by Claude Opus 5
parent 126dbf4f32
commit dc7f9f5501
5 changed files with 70 additions and 21 deletions
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src/main.cc
+33 -17
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@@ -38,6 +38,32 @@ rust::Vec<int64_t> make_vector_int(std::initializer_list<int64_t> values) {
return out;
}
void set_intrinsics(Metadata& metadata, const zed::Calibration& calib) {
metadata.set_float("fx", calib.fx);
metadata.set_float("fy", calib.fy);
metadata.set_float("cx", calib.cx);
metadata.set_float("cy", calib.cy);
metadata.set_list_float("distortion", make_distortion(calib.distortion));
}
// Both clocks are needed. The device timestamp is the instant the frame was
// captured and is the only value two nodes reading the same frame can agree on.
// The host timestamp is what the rest of the dataflow and the session recorder
// share, and on a Jetson it can step when NTP synchronises after boot — which is
// exactly why the device timestamp is recorded alongside it rather than instead
// of it.
void set_frame_stamps(Metadata& metadata, int64_t frame_id, int64_t device_ns, int64_t host_ns) {
metadata.set_int("frame_id", frame_id);
metadata.set_timestamp("device_timestamp_ns", device_ns);
metadata.set_timestamp("host_timestamp_ns", host_ns);
}
int64_t host_timestamp_ns() {
return std::chrono::duration_cast<std::chrono::nanoseconds>(
std::chrono::system_clock::now().time_since_epoch())
.count();
}
} // namespace
int main() {
@@ -80,11 +106,8 @@ int main() {
int height = image_mat.getHeight();
int64_t current_frame_id = frame_id++;
int64_t timestamp_ns = static_cast<int64_t>(
std::chrono::duration_cast<std::chrono::nanoseconds>(
std::chrono::steady_clock::now().time_since_epoch()
).count()
);
int64_t device_ns = camera.device_timestamp_ns();
int64_t host_ns = host_timestamp_ns();
// --- image_bgr ---
cv::Mat image_rgba(height, width, CV_8UC4, image_mat.getPtr<sl::uchar1>());
@@ -100,13 +123,8 @@ int main() {
image_metadata->set_string("encoding", "bgr8");
image_metadata->set_string("layout", "HWC");
image_metadata->set_list_int("shape", make_shape(height, width, 3));
image_metadata->set_float("fx", calib.fx);
image_metadata->set_float("fy", calib.fy);
image_metadata->set_float("cx", calib.cx);
image_metadata->set_float("cy", calib.cy);
image_metadata->set_list_float("distortion", make_distortion(calib.distortion));
image_metadata->set_int("frame_id", current_frame_id);
image_metadata->set_int("timestamp_ns", timestamp_ns);
set_intrinsics(*image_metadata, calib);
set_frame_stamps(*image_metadata, current_frame_id, device_ns, host_ns);
auto image_result = send_output_with_metadata(
dora_node.send_output, "image_bgr", image_slice, std::move(image_metadata));
@@ -125,11 +143,8 @@ int main() {
pc_metadata->set_string("dtype", "float32");
pc_metadata->set_string("channels", "XYZRGBA");
pc_metadata->set_string("units", "mm");
pc_metadata->set_float("fx", calib.fx);
pc_metadata->set_float("fy", calib.fy);
pc_metadata->set_float("cx", calib.cx);
pc_metadata->set_float("cy", calib.cy);
pc_metadata->set_list_float("distortion", make_distortion(calib.distortion));
set_intrinsics(*pc_metadata, calib);
set_frame_stamps(*pc_metadata, current_frame_id, device_ns, host_ns);
if (pc_mode == PcMode::HALF) {
int hw = pc_width / 2, hh = pc_height / 2;
@@ -171,6 +186,7 @@ int main() {
cam_metadata->set_string("layout", "C");
cam_metadata->set_list_int("shape", make_vector_int({4}));
cam_metadata->set_list_float("distortion", make_distortion(calib.distortion));
set_frame_stamps(*cam_metadata, current_frame_id, device_ns, host_ns);
auto cam_result = send_output_with_metadata(
dora_node.send_output, "camera_info", cam_slice, std::move(cam_metadata));