bisection_timestamp_search returns the index closest and SMALLER than the query

The bisection search used in this line returns the index closest and smaller than the query rather than the one closest to it.

See example below

timed_data = [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
query_timestamp_ns = 2.9

# If this is safe we perform the Bisection search
start = 0
end = len(timed_data) - 1
while start < end:
    mid = (start + end) // 2
    mid_timestamp = timed_data[mid]
    if mid_timestamp == query_timestamp_ns:
        start = mid
        break
    if mid_timestamp < query_timestamp_ns:
        start = mid + 1
    else:
        end = mid - 1
        
print(start, timed_data[start])  # it prints 0 1

timed_data = [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
query_timestamp_ns = 1.1

# If this is safe we perform the Bisection search
start = 0
end = len(timed_data) - 1
while start < end:
    mid = (start + end) // 2
    mid_timestamp = timed_data[mid]
    if mid_timestamp == query_timestamp_ns:
        start = mid
        break
    if mid_timestamp < query_timestamp_ns:
        start = mid + 1
    else:
        end = mid - 1
        
print(start, timed_data[start]) # This also prints 0 1

This is still buggy - will push another update later.

~~A proposed fix for the problem:~~

def bisection_timestamp_search(timed_data, query_timestamp_ns: int) -> int:
    """
    Binary search helper function, assuming that timed_data is sorted by the field names 'tracking_timestamp'
    Returns index of the element closest to the query timestamp else returns None if not found (out of time range)
    """
    # Deal with border case
    if timed_data and len(timed_data) > 1:
        first_timestamp = timed_data[0].tracking_timestamp.total_seconds() * 1e9
        last_timestamp = timed_data[-1].tracking_timestamp.total_seconds() * 1e9
        if query_timestamp_ns <= first_timestamp:
            return None
        elif query_timestamp_ns >= last_timestamp:
            return None
    # If this is safe we perform the Bisection search
    start = 0
    end = len(timed_data) - 1
    while start < end:
        mid = (start + end) // 2
        mid_timestamp = timed_data[mid].tracking_timestamp.total_seconds() * 1e9
        if mid_timestamp == query_timestamp_ns:
            return mid
        if mid_timestamp < query_timestamp_ns:
            start = mid + 1
        else:
            end = mid - 1
    
    # Get the value that is actually closest to the query timestamp
    if start + 1 < len(timed_data):
        start_timestamp = timed_data[start].tracking_timestamp.total_seconds() * 1e9
        start_plus_1_timestamp = timed_data[start + 1].tracking_timestamp.total_seconds() * 1e9
        if abs(start_timestamp - query_timestamp_ns) > abs(start_plus_1_timestamp - query_timestamp_ns):
            start = start + 1
            
    return start

Thank you, we will take a look to your code, or please do a PR for integration

We are also recommending to use the mpsDataProvider

projectaria_tools/core/python/MpsPyBind.h

Line 530 in 85ce967

"MpsDataProvider",