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waynebretl

Accuracy of photo dates by time of day and shadows

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I have done several estimates of the date a photo was taken when a clock appears in the image and the length of sun shadows can be measured. Until now, the only way to verify the result has been based on things like the weather report and the size of crowds. I recently bought a slide showing the clock and the Astral Fountain as viewed from the Meadow Lake bridge, and lucked out in that the slide had handwritten on it "Aug 9/64" and a process date of AUG64.

There were  five potentially usable shadows in the picture. I made crops of the five areas and then measured the height of people and the length of their shadows in pixels using a rectangular crop tool in Irfanview. Then I could search for the date with the same sun angle with a sun path spreadsheet.

In the crop pictures, the red lines show approximately where I made the measurements. One thing that has to be watched for is that the top of a person's head may not make the longest shadow. Also, the starting point of the shadow is where the head or shoulder goes from sunlit to shaded. For example, in crop 2, the shadow of the man's head falls on his shoulder, not on the ground. The longest shadow on the ground appears to be from his shoulder.

In crop 1, the shadow extends over the curb. I thought I could include the extra height as shown, but this gave a wildly inaccurate result (either March 27, 1964, or a date after the process month of the slide) so crop 1 was excluded from the calculations of the average.

Crop 4 is showing quite a lot of perspective tilting of the shadow, so I did a correction for perspective in lightroom and redid the calculations. I also redid an average without using crop 4.

The average date found with crops 2, 3, 4, and 5 (perspective unadjusted) was 8/4/1964, with standard deviation of 9.9 days. With crop 4 adjusted for perspective, the average was 8/5/1964, with standard deviation of 7.4 days.

The average date using crops 2, 3, and 5 was 8/8/1964, and the standard deviation was 5.5 days. A perspective correction of crop 3 would move the date closer to August 9, but probably not much.

Astral Fountain from bridge 09AUG64 2_37pm crop5.jpg

Astral Fountain from bridge 09AUG64 2_37pm.jpg

Astral Fountain from bridge 09AUG64 2_37pm crop1.jpg

Astral Fountain from bridge 09AUG64 2_37pm crop2.jpg

Astral Fountain from bridge 09AUG64 2_37pm crop3.jpg

Astral Fountain from bridge 09AUG64 2_37pm crop4 perspective.jpg

Astral Fountain from bridge 09AUG64 2_37pm crop4.jpg

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