[Qgis-user] Problems with transformation including height values
Bo Victor Thomsen
bo.victor.thomsen at gmail.com
Tue Mar 21 03:51:47 PDT 2023
Hi list -
Thanks to all for the prompt (and correct) responses.
Using ogr2ogr (and some fiddling with the csv file including a header
row..) :
ogr2ogr -dim XYZ -oo X_POSSIBLE_NAMES=x -oo Y_POSSIBLE_NAMES=y -oo
Z_POSSIBLE_NAMES=z -s_srs EPSG:4979 -t_srs EPSG:7416 -f GeoJSON
d:\temp\data_7416.json d:\temp\data_4979.csv
did the trick.
And just for the fun of it: I tried changing the input projection to
EPSG:4326:
ogr2ogr -dim XYZ -oo X_POSSIBLE_NAMES=x -oo Y_POSSIBLE_NAMES=y -oo
Z_POSSIBLE_NAMES=z -s_srs *EPSG:4326* -t_srs EPSG:7416 -f GeoJSON
d:\temp\data_7416.json d:\temp\data_4979.csv
And that didn't work. So "they" were serious about EPSG:4326 not
handling z coordinates
Med venlig hilsen / Best regards
Bo Victor Thomsen
Den 21-03-2023 kl. 11:41 skrev Nyall Dawson:
>
>
> On Tue, 21 Mar 2023, 8:21 pm Richard McDonnell,
> <richard.mcdonnell at opw.ie> wrote:
>
> Hi,
>
> Just to add to what Nyall said.
>
> See link below, which suggests a way using OGR to carry out the
> process you require.
>
> https://gis.stackexchange.com/questions/324848/transform-datum-csv-csv-using-ogr2ogr
>
> It suggests you preform your horizontal transformation first, this
> can be done in QGIS, then carry out the Vertical Transformation.
> This can be done in command line, if you are on windows, the best
> option is to use the *OSGeo4w Shell*, as all the needed
> environmental settings are applied.
>
> I hope the above helps.
>
> Maybe there is an opportunity to have QGIS preform Vertical
> translations, even if these are a separate step? It’s something
> that would be useful for both Raster and Vector Data.
>
>
> It's definitely on the radar -- especially for transformation of point
> clouds. It's just a very involved task with a high degree of
> complexity, and will need funding to happen.
>
> Nyall
>
> Regards,
>
>
> Richard
>
>
> ——
> Richard McDonnell MSc GIS, FME Certified Professional
> /FRM Data Management/
>
> ——
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>
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>
> ——
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>
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>
>
>
> ——
> MSc GIS, FME Certified Professional
>
> ——
> Oifig na nOibreacha Poiblí
> Office of Public Works
>
> Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36
> Jonathan Swift Street, Trim, Co Meath, C15 NX36
> ——
> M +353 87 688 5964 T +353 46 942 2409
> https://https://gov.ie/opw <https://www.opw.ie>
>
> ——
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>
> *From:*QGIS-User <qgis-user-bounces at lists.osgeo.org> *On Behalf Of
> *Nyall Dawson via QGIS-User
> *Sent:* 21 March 2023 10:14
> *To:* Bo Victor Thomsen <bo.victor.thomsen at gmail.com>
> *Cc:* qgis-user <qgis-user at lists.osgeo.org>
> *Subject:* Re: [Qgis-user] Problems with transformation including
> height values
>
> On Tue, 21 Mar 2023, 8:06 pm Bo Victor Thomsen via QGIS-User,
> <qgis-user at lists.osgeo.org> wrote:
>
> Hi list -
>
> I have a problem with transforming a csv file containing x,y
> /and /z values from EPSG:4326 to EPSG:7416, i.e I want to
> transform the height value from LongLat/ WGS84 ellipsoid
> height to UTM32/Etrs89 with vertical reference DVR90.
>
> The file look like this:
>
> *== data.csv, EPSG:4326 id: col1, x: col3, y: col2, z: col4 ==
> *a;55.0;12.0;42.0
> b;55.05;12.0;43.0
> c;55.10;12.0;44.0
> d;55.15;12.0;45.0
> e;55.20;12.0;46.0
> *=======================*
>
> *Step 1*: I import the file into QGIS using the Data Source
> Manager --> "Delimited Text" and define the projection to be
> EPSG:4326 /and/ to include z values. This works and the points
> are shown on my map where I expect them to be (Somewhere in
> the middle of Zealand, Denmark)
>
> *Step 2*: I export the layer as a geojson file using "Export"
> --> "Save features as.." from the layer manager and choose
> EPSG:7416 (UTM32/ETRS89 with DVR90 as vertical reference. And
> to include z-values
>
> The resulting file looks like this:
>
> *== data.geojson, EPSG:7416 ==
> *{
> "type": "FeatureCollection",
> "name": "data",
> "crs": { "type": "name", "properties": { "name":
> "urn:ogc:def:crs:EPSG::4979" } },
> "features": [
> { "type": "Feature", "properties": { "field_1": "a",
> "field_2": 55.0, "field_3": 12.0, "field_4": 42.0 },
> "geometry": { "type": "Point", "coordinates": [ 12.0, 55.0,
> 42.0 ] } },
> { "type": "Feature", "properties": { "field_1": "b",
> "field_2": 55.05, "field_3": 12.0, "field_4": 43.0 },
> "geometry": { "type": "Point", "coordinates": [ 12.0, 55.05,
> 43.0 ] } },
> { "type": "Feature", "properties": { "field_1": "c",
> "field_2": 55.1, "field_3": 12.0, "field_4": 44.0 },
> "geometry": { "type": "Point", "coordinates": [ 12.0, 55.1,
> 44.0 ] } },
> { "type": "Feature", "properties": { "field_1": "d",
> "field_2": 55.15, "field_3": 12.0, "field_4": 45.0 },
> "geometry": { "type": "Point", "coordinates": [ 12.0, 55.15,
> 45.0 ] } },
> { "type": "Feature", "properties": { "field_1": "e",
> "field_2": 55.2, "field_3": 12.0, "field_4": 46.0 },
> "geometry": { "type": "Point", "coordinates": [ 12.0, 55.2,
> 46.0 ] } }
> ]
> }
> *=======================*
>
> The new file is shown in my map exactly on top of the original
> point layer, meaning the horizontal projection is accurate.
> However, my z coordinates are not reprojected to the new
> vertical reference. All the z-values are exactly the same as
> the values in the .csv - file.
>
> After some digging through Google and other places, I discover
> that EPSG:4326 /doesn't/ have a z component. Surprise ! You
> have to use EPSG:4979, which is the same as EPSG:4326 with
> ellipsoid height.
>
> But, /after /repeating *step 1*, /but/ using EPSG:4979 as CRS
> during import, and subsequently repeating *step 2*, I get the
> exact same result: No transformation of height values.
>
> So, what is not working ? Am I doing something wrong ?? Or is
> QGIS incapable of transforming z values ???
>
> The second -- qgis currently doesn't handle vertical crs at all.
> My recommendation is to use gdal utilities to do a transform
> respecting vertical datums.
>
> Nyall
>
> --
>
> Med venlig hilsen / Best regards
>
>
>
> Bo Victor Thomsen
>
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