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<p>Thanks Dan. See my relies to Kirk and Greg. The Emlid sounds
interesting, will have a look.</p>
<p>Thanks again . . . .<br>
</p>
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Cheers, Spring</pre>
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<div class="moz-cite-prefix">On 06/Mar/2021 08:03, Dan wrote:<br>
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cite="mid:CALU7Er4oZaJ=EqL4bGmit-aUe3zP4MCf74C_Rmhc7qJvPrg1EQ@mail.gmail.com">
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<div>Kirk is spot on. That unit is for GIS use and cannot
receive RTK GNSS corrections. You will need a survey grade
receiver, with RTK corrections (or post processed) for better
accuracy.</div>
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<div>Budget option for cm accuracy is the Emlid Reach RS or RS2<br>
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<br>
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<div dir="ltr" class="gmail_attr">On Sat, 6 Mar 2021 at 23:53,
Greg Troxel <<a href="mailto:gdt@lexort.com"
moz-do-not-send="true">gdt@lexort.com</a>> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
Springfield Harrison <<a href="mailto:stellargps@gmail.com"
target="_blank" moz-do-not-send="true">stellargps@gmail.com</a>>
writes:<br>
<br>
> I recently acquired a Trimble GeoXT 2005 Series and am
puzzled by the<br>
> results it produces:<br>
><br>
> 1. Compared to a variety of "known" points, it
consistently records<br>
> positions that appear to be in error by 1.2 - 1.5 m NW
from the<br>
> known point.<br>
> 2. Points are collected and then mapped in QGIS as NAD83,
UTM Zone 10 N.<br>
> 3. The known points include property survey pins,
Government control<br>
> survey monuments, Total Station survey points derived
from the<br>
> above, other GPS results (Trimble ProXRS) and
identifiable points on<br>
> orthophotos.<br>
> 4. I'm using SBAS correction in the GeoXT.<br>
><br>
> It appears to be adding a consistent offset to the GPS
result although<br>
> no offset has been set in TerraSync.<br>
><br>
> Many thanks for any thoughts on this situation . . . . .<br>
<br>
I'm really not clear on what this particular receiver is
purporting to<br>
do, but a consistent meter-ish offset smells like an incorrect
datum.<br>
<br>
If you are using SBAS and in the US, that means WAAS. So you
are<br>
getting results that in some CRS that the list hasn't figured
out what<br>
it is, but "ITRF2008 current epoch" is my best guess. That's<br>
essentially equal to "WGS84(G1762) current epoch".<br>
<br>
Those frames are definitely not equal to any flavor of NAD83.<br>
<br>
qgis, via proj, will treat "WGS84" and "NAD83" both as datum
ensembles<br>
and because each ensemble has a low-accuracy member treat them
as equal,<br>
and thus choose a null transform. IMHO this is the wrong
thing to do,<br>
as WGS84(G1762) and NAD83(2011) are both datums with high
intrinsic<br>
accuracy and are definitely not equivalent.<br>
<br>
Converting from ITRF2014 to NAD83(2011) will apply a datum
shift.<br>
<br>
Advice 1 is to shift your project CRS from NAD83 to ITRF2014
and see if<br>
the relative position of the observations and controls
changes. If so,<br>
you have datum transform trouble.<br>
<br>
My real advice 2 is to take the data file from the unit and
label it as<br>
ITRF2014, and then see how things line up. If you are talking
about a<br>
meter you need to really pay very close attention not only to
datum<br>
labeling but also in understanding the transformations your
software is<br>
making.<br>
<br>
Greg<br>
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