[Important] Incorrect results for some Earth Engine computations, March 7-13, 2024

[Earth Engine Team]

Earth Engine developers,

From Mar 7, 2024 to Mar 13, 2024, there was a bug in Earth Engine's projection-handling logic that caused some computations to return incorrect results. You may need to re-run some computations to check their validity; please see below for details.

What was the bug?
This issue affected Earth Engine queries that use individual images in conjunction with any reprojected version of that same image ("nested reprojection"). Results generated during the timeframe may contain incorrect values due to this projection-handling error. The problem manifests as missing or misaligned image tiles, either directly or in intermediate pixel processing.

Some example code snippets that could have yielded incorrect values:

JavaScript:

var incorrectResult = img.add(img.reproject(differentProjection)); 

 

Python:

# Cloud/shadow masking using an existing cloud mask, operating

# within a radius of `BUFFER_RADIUS` pixels.

cloud_and_shadow_mask = (im.select('cloud_mask')

    .focalMin(2)

    .focalMax(BUFFER_RADIUS)

    .reproject(crs=im.select(0).projection(), scale=SCALE)

    .rename('cloud_and_shadow_mask')

    .addBands(im))

How do I know if I was affected by this bug?
Affected queries used any combination of these reprojection functions in a nested way between 2024-03-07 and 2024-03-13:
- ee.Image.changeProj()
- ee.Image.displacement()
- ee.Image.fastGaussianBlur()
- ee.Image.reduceResolution()
- ee.Image.reproject()
- ee.Image.resample()

What should I do next?
Please check the results from any queries from that time period that contained nested calls to any of the above reprojection functions. If possible, re-run your processing to ensure that your outputs are correct.

If you are a paying Earth Engine user and ran more than 100 EECU-hours of computation that may have been directly affected, we've reached out to your account representative. If you have further questions, please contact your Google Cloud sales contact or file a Cloud support ticket.

All Earth Engine users are welcome to reach out to earthengine-...@google.com with any further questions about this issue.

We apologize for the impact that this bug may have had on your work. We take the validity of scientific and operational results in Earth Engine very seriously. To prevent issues like this in the future, we have increased our automated test coverage.

Sincerely,
- The Earth Engine team