Loss in precision when using historical vs real-time data with YAMCS

[unlikelyzero]

Summary

We've been investigating an issue causing certain telemetry to plot incorrectly and noticed that float values coming from YAMCS fetch API and float values coming from websocket connections (using JSON protocol) have differing precision. This first appeared in plots, but is clearer in telemetry tables.

The values from the fetch API (historical) come in as 0.3199999928474426 for example, while realtime values through WebSocket/JSON come in as 0.32.

Interestingly, when using a websocket protobuf implementation, the precision is maintained. Meaning this is likely a problem in the JSON conversion process.

Expected vs Current Behavior

Historical and Websocket queries to return the same dataset.

Impact Check List

• Data loss or misrepresented data?
• Regression? Did this used to work or has it always been broken?
• Is there a workaround available?
• Does this impact a critical component?
• Is this just a visual bug with no functional impact?

Environment

• Open MCT Version: 3.3.0

Additional Information

Websocket JSON Implementation

Websocket protobuf Implementation

[unlikelyzero]

Root Cause yamcs/yamcs#859