# Tag Info

## Hot answers tagged datum

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### What is my coordinate system preserving?

From the links posted as comments I identified a couple of misconceptions I had about projections and gathered this quick summary. It should be mentioned that many projections don’t truly preserve ...
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### Transition to GDA2020 in QGIS?

QGIS depends on GDAL for a lot of its spatial data management. GDAL 2.2.0 should include GDA2020, as it includes updates for EPSG 8.9 and EPSG 9 (see https://trac.osgeo.org/gdal/query?group=status&...
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### Vertical Datum and Projection

No, when doing a map projection, the vertical coordinates are unaffected. If you look at the math behind a map projection (cf. Snyder's Map Projections: A Working Manual). you'll see that there's no ...
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### What is MHHW Mean Highest High Water, in terms of datums/coordinate systems?

Mean Highest High Water is a reference surface corresponding to the height of high tides, averaged over a certain period of time (usually 19 years, a value close to a Metonic Cycle and a Lunar Node ...
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### Which is the most accurate method of measuring distance?

Let me focus just on the question of the most accurate way to determine distances on the WGS84 ellipsoid. The accuracy of Vincenty's method is about 0.1 mm providing it converges. It fails to ...
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### Transition to GDA2020 in QGIS?

To add to the answer of Son of a Beach, the definitions of GDA2020 CRSs have been added to EPSG, and these have been brought into Proj4 and GDAL. These CRS definitions are good enough for many uses, ...
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### Transition to GDA2020 in QGIS?

Adding to answer by Alex Leith, the “definition” of the GDA2020 datum has been added to the EPSG registry and EPSG “Datum” codes added. See http://www.ga.gov.au/scientific-topics/positioning-...

### Which is the most accurate method of measuring distance?

For the sphere you can use the SLC (Spherical Law of Cosines). The HF (Haversine Formula) will work for this as well. You can use both of these on the ellipsoid and errors are typically very low (< ...

### Understanding EPSG in WKT

For a full understanding see the specifications: https://www.ogc.org/standards/wkt-crs Interestingly, if you look at the EPSG registry (https://epsg.org/home.html) WKT2 definitions of those two CRS ...
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### Why does WGS84 refer to so many different things?

Suppose I decided my house was the centre of everything and I wanted to define a coordinate system based on my house. I'd call this the Baz2017 Geodetic CRS. Now I need to define the Prime Meridian ...
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### Raster DEM vertical units are defined in meters, yet Arcmap displays them in feet

Sounds like somebody converted the raster values to feet, but didn't update the metadata. Arcmap doesn't actually "know" anything about the vertical units your raster is in, it's just reporting the ...
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### Defining Latitude and Longitude before defining Datum?

Latitude and Longitude are defined upon an ellipsoid. Essentially you can have different lon/lat. NAD 27 lon/lat and WGS84 lon/lat will have subtle differences. As a rule, when people nowadays ...

### What datums were used in North America before NAD27?

New England Datum of 1879 Was the first geodetic datum of this type in the United States. The reference ellipsoid was Clarke Ellipsoid of 1866. United States Standard Datum of 1901 (First North ...
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### Seems that there is no tag for datums or coordinate system in KML file?

Quoting from here which seems to be a copy of the standard but not in PDF. KML relies on a single Coordinate Reference System, which is not referenced explicitly in KML files. The encoding of ...
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### What's the best way to handle a 'Site Datum' in QGIS?

You can do both: At Using customized Coordinate System in ArcGIS Desktop? I have explained how to set up a local CRS based on the origin of the local system. The data in the local CRS remains ...
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### Problem with MGI CRS on the Balkan

The MGI 1901 projection is ok. The Austrian surveying authority changed their MGI datum in the 1920ies, but the Yougoslav surveying authority did not follow, Hence they still surveyed in MGI 1901. The ...
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### Representing heights in GIS?

The term you are looking for is 'Vertical Datum'. It is the same really as co-ordinates such as latitude & longitude. These X & Y measurements (be it degrees or metres) only make sense when ...
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### Determining Layer's DATUM and PROJECTION in "Layer Properties" (QGIS)

You can always find all corresponding information about certain projection by its standard EPSG code on spatialreference.org. For example, your Layer 1 has EPSG code of "2203", so here is all ...
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### Adequate proj4string for ETRS89

Finding the proper proj4-string can be a bit funny. Such strings provide information on both the ellipsoid and how coordinates on the surface are arranged. Deciphering your example gives us the ...
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### Reproject in QGIS doesn't work the way like in ArcGIS

The fact that they have exactly the same shape and are laterally offset by just a few meters suggests the conversion to a projected CRS is fine but the result has been projected on a slightly ...

### PostGIS ST_Transform seems to treat the vertical datum but not the equivalent pyproj Transformer, even so they both rely on Proj

One thing to note is the version of PROJ that is being used. PostGIS in your version is using PROJ 5.2 and the version of pyproj you are using is likely using PROJ 7.2+. There are quite a few things ...
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### Convert Vertical Datum of GDAL file

Your syntax works for me with Proj version 8.1.1, at least the Z coordinates are changing. gdaltransform -s_srs EPSG:4326+5773 -t_srs EPSG:4979 Enter X Y [Z [T]] values separated by space, and press ...
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### Finding vertical datum for bathymetry layer?

The datum will only be specified if the creator of the dataset put it in there. If you're given a dataset and it's missing the coordinate system, datum, or both (horizontal or vertical), you'll need ...
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### Meaning of "Elevation above surface of ellipsoid"?

HAE, or Height Above Ellipsoid, or "elevation above surface of ellipsoid", is commonly the form of altitude a GPS receiver returns. It differs from AGL (height above ground level) and MSL (...
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### Handwritten cordinates from eTrex 10

I hope this may help you. I did some research on Sri Lanka coordinate systems at spatial reference. I found some crs that may apply to your problem. For testing purposes I used EPSG 5324 (Kandawala / ...
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### Performing QGIS Datum Transformation from WGS 1984 to NAD 1983?

You may try to perform these steps: Create new QGIS blank project; Only load the shapefile which has the WGS84 as CRS; Right-click on the loaded layer from the Layers Panel and click on Save As... ...
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### Performing QGIS Datum Transformation from WGS 1984 to NAD 1983?

As long as everything is configured correctly on your GPS receiver, and it was clear skies, and there weren't any buildings obstructing your receiver, then I would say that the points you collected ...
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### Convert NGVD 1929 to NAVD 1988?

NOAA distributes an application called VDatum which will do vertical datum transformations. VDatum is free and cross platform but it is a Java application so you will need to install Java. VDatum ...
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