Welcome to this comprehensive QGIS technical guide. When extracting point elevations, contour data, or digital elevation models (DEMs) into attribute tables, engineers frequently encounter an issue where Z-values or coordinate decimals are automatically rounded off to whole numbers. This lack of precision causes discrepancies in terrain modeling, earthwork calculations, and profile designs.

Tutorial Overview: This guide walks you through diagnosing why QGIS rounds attribute table decimals and how to unlock full floating-point precision to extract exact XYZ coordinates and Z-elevation values for professional engineering workflows.

QGIS Precision Parameters & Attribute Fixes

Correcting attribute field properties and export settings ensures that your topographical data retains sub-meter accuracy for civil and hydraulic infrastructure projects.

Diagnostic Issue	QGIS Tool / Panel	Engineering Solution
Rounded Z-Values	Layer Properties > Fields	Changing field data type from Integer to Decimal Number (Real) with explicit precision limits.
Expression Calculations	Field Calculator (`$z` or `$x` / `$y`)	Using geometry expressions to re-extract exact floating-point coordinates directly from point vertices.
Data Export Settings	Export Layer As... > CRS Options	Ensuring coordinate precision settings are not truncated during CSV, DXF, or Shapefile conversions.

Step-by-Step Workflow to Fix Rounded Elevation Values

1. Identifying the Field Type Limitation (Before vs After Comparison)

Open your attribute table and inspect the columns. As shown in the comparison below, rounded attributes display flat whole numbers before correction, whereas properly configured decimal fields retain exact millimetric coordinate precision after correction.

2. Adjusting Field Properties and Precision

Enable editing mode in your vector layer, open the **Field Calculator**, or modify the field properties through the layer settings. Ensure that the precision parameter (decimal places) is set to 3 or more to capture millimetric elevation accuracy.

3. Extracting Precise Geometry Coordinates

Use expression strings in the Field Calculator (such as `$z` for elevation, `$x` for Easting, and `$y` for Northing) to overwrite or generate new attribute columns containing unrounded, high-precision floating-point numbers.