Trimble Pathfinder Differential Correction: ‘Uncorrected’ for block of GPS data

Question

I’ve been collecting GPS point data without problems over the last few months. Recently, on two dates, after using Pathfinder differential correction, the exported records’ Corr_Type changed from Postprocessed Code to Uncorrected. In other words, the records are Postprocessed Code (which is what I want to see) up to a certain point, but the subsequent records are Uncorrected. It may be a coincidence, but the problem occurs on the change of the hour.

Date Time Corr_Type
6/24/15 0:00 09:38:39am Postprocessed Code
6/24/15 0:00 09:40:55am Postprocessed Code
6/24/15 0:00 09:43:54am Postprocessed Code
6/24/15 0:00 09:45:27am Postprocessed Code
6/24/15 0:00 09:46:25am Postprocessed Code
6/24/15 0:00 09:47:48am Postprocessed Code
6/24/15 0:00 09:52:31am Postprocessed Code
6/24/15 0:00 09:54:58am Postprocessed Code
6/24/15 0:00 09:55:46am Postprocessed Code
6/24/15 0:00 09:56:55am Postprocessed Code
6/24/15 0:00 09:58:51am Postprocessed Code
6/24/15 0:00 10:02:01am Uncorrected
6/24/15 0:00 10:04:00am Uncorrected
6/24/15 0:00 10:05:18am Uncorrected
6/24/15 0:00 10:07:06am Uncorrected
6/24/15 0:00 10:09:43am Uncorrected
6/24/15 0:00 10:11:09am Uncorrected
6/24/15 0:00 10:13:14am Uncorrected
6/24/15 0:00 10:14:20am Uncorrected
6/24/15 0:00 10:16:09am Uncorrected
6/24/15 0:00 10:17:48am Uncorrected
6/24/15 0:00 10:20:22am Uncorrected
6/24/15 0:00 10:24:06am Uncorrected
6/24/15 0:00 10:26:04am Uncorrected
6/24/15 0:00 10:28:18am Uncorrected
6/24/15 0:00 10:29:09am Uncorrected
6/24/15 0:00 10:30:10am Uncorrected
6/24/15 0:00 10:32:32am Uncorrected
6/24/15 0:00 10:35:39am Uncorrected
6/24/15 0:00 10:36:22am Uncorrected

Date Time Corr_Type
6/25/15 0:00 10:45:50am Postprocessed Code
6/25/15 0:00 10:48:38am Postprocessed Code
6/25/15 0:00 10:49:44am Postprocessed Code
6/25/15 0:00 10:51:03am Postprocessed Code
6/25/15 0:00 10:52:34am Postprocessed Code
6/25/15 0:00 10:53:29am Postprocessed Code
6/25/15 0:00 10:56:40am Postprocessed Code
6/25/15 0:00 10:58:28am Postprocessed Code
6/25/15 0:00 10:59:48am Postprocessed Code
6/25/15 0:00 11:00:36am Postprocessed Code
6/25/15 0:00 11:03:00am Postprocessed Code
6/25/15 0:00 11:03:45am Postprocessed Code
6/25/15 0:00 11:05:49am Postprocessed Code
6/25/15 0:00 11:08:05am Postprocessed Code
6/25/15 0:00 11:12:59am Postprocessed Code
6/25/15 0:00 11:14:52am Postprocessed Code
6/25/15 0:00 11:16:38am Postprocessed Code
6/25/15 0:00 11:17:28am Postprocessed Code
6/25/15 0:00 11:18:26am Postprocessed Code
6/25/15 0:00 11:19:37am Postprocessed Code
6/25/15 0:00 11:21:10am Postprocessed Code
6/25/15 0:00 11:26:08am Postprocessed Code
6/25/15 0:00 11:29:17am Postprocessed Code
6/25/15 0:00 11:32:36am Postprocessed Code
6/25/15 0:00 11:40:47am Postprocessed Code
6/25/15 0:00 11:45:14am Postprocessed Code
6/25/15 0:00 11:48:17am Postprocessed Code
6/25/15 0:00 11:58:18am Postprocessed Code
6/25/15 0:00 12:04:29pm Uncorrected
6/25/15 0:00 12:06:28pm Uncorrected
6/25/15 0:00 12:09:01pm Uncorrected
6/25/15 0:00 12:10:57pm Uncorrected
6/25/15 0:00 12:13:51pm Uncorrected
6/25/15 0:00 12:16:23pm Uncorrected
6/25/15 0:00 12:17:29pm Uncorrected
6/25/15 0:00 12:18:47pm Uncorrected
6/25/15 0:00 12:20:37pm Uncorrected
6/25/15 0:00 12:24:01pm Uncorrected
6/25/15 0:00 12:25:01pm Uncorrected
6/25/15 0:00 12:26:10pm Uncorrected
6/25/15 0:00 12:27:45pm Uncorrected
6/25/15 0:00 12:29:23pm Uncorrected
6/25/15 0:00 12:32:55pm Uncorrected
6/25/15 0:00 12:34:59pm Uncorrected
6/25/15 0:00 12:38:38pm Uncorrected
6/25/15 0:00 12:40:29pm Uncorrected
6/25/15 0:00 12:42:14pm Uncorrected
6/25/15 0:00 12:44:05pm Uncorrected
6/25/15 0:00 12:47:16pm Uncorrected
6/25/15 0:00 12:49:06pm Uncorrected

I haven't noticed anything peculiar on the GPS receiver itself that might indicate a problem during data collection.

I've done the differential correction on the same day as when the data were collected, and also on subsequent dates, so I don't believe this is a CORS hourly vs. daily issue.

Anyone have an idea on what's causing this (and how to prevent it)?

Answer 1

I assume the positions which do not post-process are in similar GPS conditions to positions which do post-process (i.e. you are not randomly walking under trees every hour and standing in the open the rest of the time.)

In my experience (I use Trimble TerraSync and PathFinder Office post-processing at least once a week) the most likely cause of problems like this which occur on hour boundaries is some problem in the base data you use, not a data collector problem. For example, a few minutes of data is missing at the start of the hour.

Things you could try:

• If you know what you are doing, look for missing epochs in the base data.
• Try post-processing using a different base station (preferably one which uses a GNSS receiver from a different manufacturer)
• If Pathfinder Office offers "Hourly" and "Daily" versions of the base station, try the "Daily" version (I assume you normally use the "Hourly" version if both are available.)

Answer 2

I have corrected these types of errors before by making copies of the CORS base stations' properties, and changing the internet server property parameter "&duration=%LL%&" to "&duration=24&". This tells the service to download 24 hours worth of data, ensuring 100% coverage for processing. Otherwise I consistently get 24% coverage...

In Utilities > Differential Corrections > Base Provider Search > Select > then highlight the CORS station you want to use, and click "Copy". From there, go to "Internet Server" and change the Base File Address Format as above...