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<pre class="moz-quote-pre" wrap="">Certainly, a program that uses coordinates is going to have a working
CRS, what we'd call "project CRS" in qgis. That's a choice by the
project/program.
</pre>
</blockquote>
So far we agree 100% :)<br>
<br>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">Then, using a GNSS receiver, it's going to get coordinates in some CRS.
Even without using NTRIP and injecting corrections/reference-data,
exactly what CRS is a difficult question. Today, it could be
WGS84(G2296), or it could be some ITRF if using WAAS or EGNOS. Once you
inject corrections, it could be quite a variety of CRSes.
I don't see how "the NTRIP corrections have to match". What's available
is going to be constrained.</pre>
</blockquote>
Again I totally agree with you. However if corrections don't match
the project CRS, most users would not want to have a datum
transformation automatically applied without them being notified. I
for one, would hate to have software do a DT without me saying so.
That is why I said that I see Javier's database as a verification
tool. I'd like the software popping a big red flag saying "Wait!
your GPS corrections don't match the project CRS! What should I do?"<br>
<br>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">NTRIP is simply a way to ask for a corrections stream.</pre>
</blockquote>
Not only. It also gives you some additional information like
organization supplying those, location of base station, if you need
to send a GGA sentence, bit rate, and so on. It would be nice if the
CRS of those corrections would be part of that info.<br>
<br>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">If you are getting a corrections stream not over NTRIP, because it's raw
TCP, or serial data radio, you still want to know the frame.</pre>
</blockquote>
Indeed, but if you get corrections over a radio link, you, or a
buddy of yours, has set up the base station and you know the CRS.
Same thing if you use raw TCP: you probably contacted the
organization that sends the corrections to find out IP addresses
port numbers and what not. At that time, you probably asked what CRS
they are using for their base.<br>
<br>
With NTRIP casters you have no way to a priori know the CRS of a
stream. I agree that having CRS info in the stream itself is very
useful , but if you have to choose what stream to use from the 100+
streams advertised by a caster, checking them one by one to find the
proper CRS very difficult. You could check them using Javier's
database, but I still believe it would be simpler if casters would
directly provide that information.<br>
<br>
<br>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">I don't understand your comments at all.
</pre>
</blockquote>
Hopefully now my comments make more sense.<br>
<br>
<br>
Cheers,<br>
Mircea<br>
<br>
<br>
<div class="moz-cite-prefix">On 3/25/2025 3:55 PM, Greg Troxel via
PROJ wrote:<br>
</div>
<blockquote type="cite" cite="mid:rmi5xjwj35d.fsf@s1.lexort.com">
<pre class="moz-quote-pre" wrap="">Mircea Neacsu via PROJ <a
class="moz-txt-link-rfc2396E" href="mailto:proj@lists.osgeo.org"><proj@lists.osgeo.org></a> writes:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">I find your project a valuable initiative. I see it mostly as a
verification tool, not as an automatic CRS selection tool. In most
cases the CRS selection is imposed by other considerations and the
NTRIP corrections have to match that selection.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">I don't understand your comments at all.
Certainly, a program that uses coordinates is going to have a working
CRS, what we'd call "project CRS" in qgis. That's a choice by the
project/program.
Then, using a GNSS receiver, it's going to get coordinates in some CRS.
Even without using NTRIP and injecting corrections/reference-data,
exactly what CRS is a difficult question. Today, it could be
WGS84(G2296), or it could be some ITRF if using WAAS or EGNOS. Once you
inject corrections, it could be quite a variety of CRSes.
I don't see how "the NTRIP corrections have to match". What's available
is going to be constrained. Around me, the only real option without
paying is EPSG:6319. So then a program receiving coordinates in the
frame of the correction source, can transform into the project CRS.
That's pretty straightforward, and one just has to know the correction
source CRS.
Regardless of how you deal with the above, the key point is that one
wants to know, for a given source, what is the frame of the corrections.
That can be verification if you configure what you expect, and it can be
automation if you don't.
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">In regard to other comments on the list: the way I see it, information
about the CRS associated with a corrections stream should have been
included in NTRIP protocol. The fact that now it exists in RTCM 3.4,
is good but it's not the proper place. Once you have selected a
corrections stream you can only check that corrections match your
intended CRS. Besides, what if you need corrections in a different
format (CMR or something else)? My view is that this information
should be provided by the NTRIP casters.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">NTRIP is simply a way to ask for a corrections stream. The frame of a
stream is just as much a part of it as is the base station coordinates.
If you are getting a corrections stream not over NTRIP, because it's raw
TCP, or serial data radio, you still want to know the frame. So I think
it absolutely belongs in RTCM. People using CMR should ask their
proprietary equipment vendors to create a CMR+crs definition, but
probably the plan would be to figure out how to stop using CMR :)
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</pre>
</blockquote>
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