Observation file too large for OPUS

I tried uploading an observation file to OPUS and got a message back saying, “Request Entity Too Large” I logged data for four hours using the OPUS preset in Emlid Flow. The observation file is 72.3MB.

Does anyone know what the largest file OPUS will accept is? Is there a way to reduce the file size so OPUS can process it?

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Decimate the session file to 15 seconds epoch seems like you used very fast epoch (less than 1 second??

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If your existing file is too large, you can use the free Teqc (TEQC | Software | UNAVCO) to downsample the Rinex file to a lower sampling interval by using this command:

teqc -O.int 0.2 -O.dec 30 .16o > _decim30s.23o where -O.int is the observation interval (here, 0.2 sec or 5 Hz) and -O.dec is the decimated data interval (here, 30 sec).

@JoBind Thanks, I’ll give it a try.

I’m pretty sure I used OPUS preset in Emlid Flow, which defaults to 30 second intervals and GPS only, but maybe not…

Hi Eric,

Yep, the OPUS preset has a default logging interval of 30 seconds. It’s done precisely in order to reduce the weight of the log.

Can you please share your log with me? As far as I remember, OPUS allows uploading files of up to 100 MB. So I’ll check what may be the issue.

@julia.shestakova OPUS told me the limit on log files is 60MB. How do I share my log file with you? The upload button won’t accept a .23O file.

@dronemapper23 - Hi Eric,

Wow. 72.3 MB for 4 hours!

I don’t know, in answer to your question, “Does anyone know what the largest file OPUS will accept is?” and I can’t say I’ve ever tried to upload a file of that size to OPUS.

First, you should study the FAQs on this page:



This means that 1-sec GPS-only data will by default be decimated to 30-sec by OPUS. The main advantage of either decimation, or recording long static obs sessions at 30-sec epochs is file size.

Also be aware that OPUS has a maximum obs time span of 48 hours wherein you can only cross midnight Zulu once.

@JoBind Jo +1 Thanks for this link!
I used to use it once in a while, but prefer using GFZRNX for several reasons after I started using GFZRNX when I was helping a surveyor in 2021 that is still using his Ashtech Z-Xtreme receivers, and wrangling his data and shifting (-shift_gpsw RINEX File Manipulation - GFZRNX 2.0.2 Users Guide) it to accommodate the April 2019 GPS week rollover event. Check it out: https://gnss.gfz-potsdam.de/services/gfzrnx/download


As an example, I recorded a 9 hour observation today. I converted the raw observation file (ubx) from the RS2+ using Emlid Studio to a couple of different rinex file options.

  1. All satellites at 1 hz. resulted in a 150 Mb obs file.
  2. GPS only at 30 seconds resulted in a 1.4 Mb obs file

@dpitman Thanks Dave!

Just curious,

  • what software did you use for the UBX2RNX conversion?
  • what software did you use for the GPS_only & decimation?
  • were you able to combine conversion, filtering, and decimation in a single pass?

Kelly, all using Emlid Studio for the conversion and decimation.

Another little test. When recording the log wth the RS2+, I also recorded a rinex using the OPUS preset. I then compared that rinex obs file with the converted decimated file out of Emlid Studio, and they were basically identical looking at the file charted in ES.

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Hi Eric,

You can send it to support@emlid.com using any file-sharing service available to you (for example, WeTransfer). We’ll check it.

Hi Eric,

I checked the log that you shared with me. The size of the file is big because there were multiple GNSS systems selected and recorded with a 1-second update rate.

I converted your file in Emlid Studio selecting GPS system only and choosing an interval of 30 s. The file was successfully uploaded to OPUS. I’ll send you this converted file via email.

The OPUS preset in Emlid Flow automatically sets the GPS only for Satellite systems and 30 s Logging interval.

@liudmila.slepova Thanks, I thought I had selected the OPUS preset in Emlid Flow, but apparently I didn’t. I will make sure GPS only and 30 second intervals are selected the next time I log for OPUS.

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