The centroid-to-centroid distance between an object & itself can be > 0

[petebankhead]

Bug report

Describe the bug
See https://forum.image.sc/t/distances-between-objects-and-annotations/77933

To Reproduce
Steps to reproduce the behavior:

1. Open an image
2. Detect and classify cells (e.g. with Positive cell detection)
3. Run Analyse → Spatial analysis → Detect centroid distances 2D
4. Check the distance for several objects between themselves and objects with the same class. This is usually 0, but can be greater than 0.

Expected behavior
The distance between an object and itself should always be 0.

The underlying issue seems to be a rounding error due to the way the calculation is performed:

qupath/qupath-core/src/main/java/qupath/lib/analysis/DistanceTools.java

Line 358 in 1368912

public static void centroidToCentroidDistance2D(Collection<PathObject> sourceObjects, Collection<PathObject> targetObjects, double pixelWidth, double pixelHeight, String measurementName) {

This involved converting objects to points, and the geometries will likely have precision models applied.

Desktop (please complete the following information):

• OS: Likely all
• QuPath Version: 0.4.3 (but no known relevant changes made recently, so probably earlier versions too)

Additional context
When fixing this, it may also be possible to make the calculation more efficient by checking for object matches in the source and target list.