eventcv_core/representation/
time_surface.rs

1use super::{
2    age_ms, event_index, frame_len, reference_time, validate_positive, EventFrame, EventFrameData,
3    Representation, RepresentationError, RepresentationKind,
4};
5use crate::EventStream;
6
7#[derive(Clone, Copy, Debug)]
8pub struct TimeSurface {
9    tau_ms: f64,
10}
11
12impl TimeSurface {
13    pub fn new(tau_ms: f64) -> Self {
14        Self { tau_ms }
15    }
16}
17
18impl Default for TimeSurface {
19    fn default() -> Self {
20        Self::new(30.0)
21    }
22}
23
24impl Representation for TimeSurface {
25    type Output = EventFrame;
26
27    fn generate(&self, stream: &EventStream) -> Result<EventFrame, RepresentationError> {
28        validate_positive(self.tau_ms, "tau_ms")?;
29        let (width, height, length) = frame_len(stream, 2)?;
30        let plane_len = width * height;
31        let mut latest = vec![None; length];
32
33        for event in stream.iter() {
34            let index =
35                event_index(event, width, height)? + if event.polarity { 0 } else { plane_len };
36            if latest[index].is_none_or(|timestamp| event.timestamp > timestamp) {
37                latest[index] = Some(event.timestamp);
38            }
39        }
40
41        let mut values = vec![0_f32; length];
42        if let Some(reference) = reference_time(stream) {
43            for (value, timestamp) in values.iter_mut().zip(latest) {
44                if let Some(timestamp) = timestamp {
45                    *value = (-age_ms(stream, reference, timestamp) / self.tau_ms).exp() as f32;
46                }
47            }
48        }
49
50        Ok(EventFrame {
51            data: EventFrameData::F32(values),
52            channels: 2,
53            width,
54            height,
55            kind: RepresentationKind::TimeSurface,
56            channel_names: vec!["positive".to_owned(), "negative".to_owned()],
57        })
58    }
59}
60
61#[cfg(test)]
62mod tests {
63    use ndarray::array;
64
65    use super::{Representation, TimeSurface};
66    use crate::{representation::EventFrameData, EventStream};
67
68    #[test]
69    fn uses_latest_event_per_pixel_and_polarity() {
70        let stream = EventStream::from_array2(
71            array![[0, 0, 30_000, 1], [1, 0, 20_000, 0], [0, 0, 10_000, 1]],
72            2,
73            1,
74            0.001,
75        );
76
77        let frame = TimeSurface::new(10.0).generate(&stream).unwrap();
78        let EventFrameData::F32(values) = frame.data() else {
79            panic!("time surfaces must use float32 data");
80        };
81
82        assert_eq!(values[0], 1.0);
83        assert_eq!(values[1], 0.0);
84        assert!((values[3] - (-1.0_f32).exp()).abs() < 1e-6);
85    }
86}
eventcv_core/representation/time_surface.rs

eventcv_core/representation/
time_surface.rs
