[Qgis-user] Problems with transformation including height values

Tue Mar 21 03:21:41 PDT 2023

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.
Regards,

Richard

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Richard McDonnell MSc GIS, FME Certified Professional
FRM Data Management

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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<mailto: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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