InfluxDB: synchronize timestamps between topics for use in Grafana Geomap

Question

I have latitude/longitude values being put into an InfluxDB instance under different topics. They are provided via MQTT, e.g. topics are foo/bar/lat and foo/bar/lon with the coordinate values as float strings in the message part. These are then processed sequentially by Telegraf.

So each positioning event results in a 2-tuple of entries in different series that have slightly different timestamps. The ∆ is typically below 1 millisecond whereas the events are several seconds (or more) apart due to the processing in Telegraf.

When visualizing this in Grafana using a Time Series or (old) Graph panel, the difference does not matter, but the Geomap panel does not recognize the lat/lon values as actual coordinate pairs, so no data are displayed.

How can I write the queries (or a single query?) such that the timestamps are matched? Or can I prevent the timestamps from differing when being processed in Telegraf? There is no actual timestamp in the data sent over MQTT.