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<p>Hi,</p>
<p class="MsoNormal"> First post to this group and a relative
novice to PROJ, beyond using existing transformation strings. I'm
looking to implement transformations to and from HS2 NTv2 and
OSTN02 and OSTN15, and also matching vertical shifts, using Proj
(current v7 build, working in C++), see <a
href="https://www.thepwi.org/technical_hub/presentations_for_tech_hub/190709_summer_nr_tech/07_hs2_engineering_coordinate_systems__j_turner">https://www.thepwi.org/technical_hub/presentations_for_tech_hub/190709_summer_nr_tech/07_hs2_engineering_coordinate_systems__j_turner</a>
for a description of the HS2 NTv2 grid which replaces the HS2
Snakegrid implementation. HS2 grid is registered under
EPSG:9300: <a
href="https://epsg.org/crs_9300/HS2-Survey-Grid.html?sessionkey=wbkmhx76b2">https://epsg.org/crs_9300/HS2-Survey-Grid.html</a>
And the compound CRS is registered under EPSG:9306: <a
href="https://epsg.org/crs_9306/HS2-Survey-Grid-HS2-VRF-height.html?sessionkey=oryxvd4m1b">https://epsg.org/crs_9306/HS2-Survey-Grid-HS2-VRF-height.html</a></p>
<p>I have the NTv2 GSB files for HS2 NTv2 (HS2TN15_NTv2.gsb and
HS2TN02_NTv2.gsb) and will be transforming between 3d coordinates,
where from my understanding height and grid position will be dealt
with separately. I also have vertical shift files in the format
lat, long, height which I'm guessing I'll need to convert to a GTX
file as described here; <a
href="https://vdatum.noaa.gov/docs/gtx_info.html">https://vdatum.noaa.gov/docs/gtx_info.html</a>
Not sure whether PROJ uses ASCII or binary versions of the GTX
file, but no issues building either as needed.<br>
</p>
<p>What I'd like to achieve is a PROJ string or pipeline I can use
within my software to perform the required transformations, i.e.
OSTN02 & OSGM02 and OSTN15 & OSGM15 to HS2 survey grid
plus VRF and back again. <br>
</p>
<p>While I can probably work my way through this, as someone new
using GSB and GTX files in PROJ, any help or suggestions would be
greatly appreciated. I was hoping it would be available in
epsg.io but it seems not as yet,<br>
</p>
<p>Shane<br>
</p>
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