How to update coordinates by values in columns?

Question

I try to make a script which changes the coordinates given in format DMS (like N54 24 04.50, E018 34 17.20 to 18.6889, 54.3320) to DD format which is suitable for working in QGIS. The conversion is pretty easy but what I want to really do is to change a point position basing on coordinates given in columns. Like here:

So I want to create a feature, then type in LAT and LON columns the desired position, columns 'x' and 'y' shall take these coordinates and convert them to DD format. And the last step is to change the feature position basing on columns 'x' and 'y'.

I know that I can retype the coordinates or recalculate them in csv. sheet and load again to QGIS but it's time consuming. So is there a possibility to 'set' a columns from which the feature will take the $x and $y of geometry directly in QGIS?

Answer 1

Absolutely, via Field calculator in your attribute table. First, you need to create a text field that includes both the Lat Long values as a WKT Text Point input, such as "Point (-40.7 15.397)". As you noted, these can't be inputted as variables directly to the geom_from_wkt function call. Create a new field, of type Text, and populate with your X and Y columns, with the expression concat( 'Point ( ',"X",' ',"Y", ' )') like this:

Be sure to set the field length to 40 to avoid cutting off the statement. Then, you'll want to check the box for "Update existing field", and pass this WKT field to the geometry function. Select geometry from the drop down list. Then, you can either type the function directly into the Expression box or select it from the Geometry function drop-down menu: geom_from_wkt. You'll enter:

geom_from_wkt( "WKT" )

After updating this, you'll need to save edits, as this will open an edit session and update all the features directly. Here's a view of what your Field Calculation should be:

Now, if you want to bypass the attribute table directly, you can use the NODE tool, with your QGIS editor toolbar: When you click a point with this tool, it will bring up the Vertex Editor window that will allow you to manipulate positions directly by typing values. However, this is a tedious process, and I would suggest using the Field Calculator.