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Overlong RTCM3 packets from EUREF-IP

From: Marek Szuba
Subject: Overlong RTCM3 packets from EUREF-IP
Date: Tue, 29 Sep 2020 14:24:18 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0

Hello again,

Having accidentally found out during my struggle with the GNSS time
source that gpsd supports NTRIP, I decided to try integrating it into my
poor man's WiFi signal-strength mapper in place of the separate client I
used to use earlier. My NTRIP caster ( uses RTCM 3.3 but no
problem here, a quick look at gpsd-3.21 source code showed that it
should be able to handle this version. What HAS turned out to be the
problem is that I immediately began to get "overlong RTCM3 packet"
errors... The largest packet I have seen so far was 590 bytes long,
which indeed is larger than the hard-coded limit of 512 bytes.

Unfortunately I do not own a copy of RTCM 10403.3 so I do not know what,
if anything, the specifications say about maximum packet length. That
said, having randomly sampled the source code of various NTRIP clients
and servers listed at (under the
assumption that BKG of all people should know how to handle NTRIP
correctly) it seems 2048 bytes is the most common value for this.
Indeed, replacing 512 with 2048 in the source code seems to make
gpsd-3.21 handle EUREF RTCM data just fine.

What do you think about about increasing RTCM3_MAX to 2048, guys?


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