Clock offset (exif_time_infront_real_time) is not applied to Experiment_Time[s]

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@kriboe90 已经在做这个了。

开始于 2026年10月29日。

  • #174 来自 @kriboe90 —— 未关闭

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调研方向

从 ledsa/data_extraction/init_functions.py 中的 _calc_experiment_and_real_time 开始，并将其时间计算与 ledsa/core/ConfigData.py 中的 ConfigData.get_start_time 进行比较。为以下情况添加回归测试：第一张图像的 start_time 来自其 EXIF 时间，以及两台偏移量不同的相机。完成标准是这两种情况都生成预期的实验共享时间轴；更新配置文档，说明手动设置的 start_time 使用实际时钟时间。

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描述

bug

Problem

The camera clock offset exif_time_infront_real_time is only applied to Time[s]. It never reaches Experiment_Time[s].

  • ConfigData.get_start_time moves start_time onto the real clock: it subtracts the offset from the EXIF time of the first image (ConfigData.py#L494).
  • _calc_experiment_and_real_time then measures the experiment time from the uncorrected EXIF time (init_functions.py#L130):
experiment_time = date_time_img - config.get_datetime()   # camera clock − real clock
...
time = date_time_img - timedelta(seconds=time_diff)        # only Time[s] is corrected

So every Experiment_Time[s] is off by exif_time_infront_real_time.

Effects

  • One camera: every time moves by the same amount. When start_time comes from the first image, that image sits at t = offset instead of 0. A temperature reduction table built on the lab clock is read that many seconds off.
  • Several cameras: the stacked analysis matches the cameras by Experiment_Time[s] (_load_time_map → read_experiment_times, StackedExtinctionCoefficients.py#L575). Their time axes stay apart by the difference of their offsets, which is the gap the clock photos were meant to remove.

Reproduction

Camera clock 30 s ahead, one image every 10 s, start_time left to be read from image 1 (EXIF times faked):

start_time = 12:00:00
#Count,Name,Time[s],Experiment_Time[s]
1,img0001.jpg,12:00:00.000,30.0
2,img0002.jpg,12:00:10.000,40.0
3,img0003.jpg,12:00:20.000,50.0

Time[s] of image 1 equals start_time, yet its experiment time is 30 s.

Suggested fix

Measure the experiment time from the corrected time, the same way start_time is computed:

     date_time_img = get_exif_datetime(img_path, tag)

-    experiment_time = date_time_img - config.get_datetime()
-    experiment_time = experiment_time.total_seconds()
     time_diff = config.getfloat(build_type, 'exif_time_infront_real_time')
     time = date_time_img - timedelta(seconds=time_diff)
+    # start_time is on the real clock, so the experiment time is measured from the corrected image time
+    experiment_time = (time - config.get_datetime()).total_seconds()
     return experiment_time, time

With this change the reproduction gives 0, 10, 20 s, and the existing unit tests (370) still pass. A regression test should cover two cases:

  1. With start_time derived from the first image, that image is at 0.
  2. Two cameras with offsets of +30 s and −5 s and the same start_time give the same experiment times.

Things to note

  • Semantics of a hand-set start_time: after the fix, start_time is read as a real-clock (lab) time, as it already is when LEDSA derives it. The config docs should say so explicitly.
  • Existing results: image_infos*.csv written before the fix, and everything built on them, are shifted by the offset. They must be regenerated, and so must any temperature reduction table that was aligned to the old axis. The demo has time_diff_to_image_time = -1, so its times move by 1 s.
  • Multi-camera, out of scope here: even after the fix, cameras share a time axis only when their start_time is the same real time. If each camera derives start_time from its own first image, the axes still differ by the gap between those first images. It may be worth a check or a warning in the stacked analysis.
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