fix: use MetadataUtils.relative paths where applicable

* and add more tests

src/main/java/org/janelia/saalfeldlab/n5/universe/metadata/ome/ngff/v04/OmeNgffMultiScaleMetadata.java

@@ -26,8 +26,6 @@
 package org.janelia.saalfeldlab.n5.universe.metadata.ome.ngff.v04;
 
 import java.net.URISyntaxException;
-import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.Arrays;
 import java.util.stream.DoubleStream;
 
@@ -139,11 +137,9 @@ private static OmeNgffDataset[] buildDatasets( final String path, final NgffSing
 		for( int i = 0; i < children.length; i++ )
 		{
 			datasets[i] = new OmeNgffDataset();
-//			final Path p = Paths.get(path);
-//			final Path c = Paths.get(children[i].getPath());
-//			datasets[i].path = p.relativize(c).toString();
-			datasets[i].path = Paths.get(path).relativize(Paths.get(children[i].getPath())).toString();
+			datasets[i].path = MetadataUtils.relativePath(path, children[i].getPath());
 			datasets[i].coordinateTransformations = children[i].getCoordinateTransformations();
+
 		}
 		return datasets;
 	}

src/main/java/org/janelia/saalfeldlab/n5/universe/metadata/ome/ngff/v04/OmeNgffMultiScaleMetadataMutable.java

@@ -57,12 +57,7 @@ public void addChild(final int idx, final NgffSingleScaleAxesMetadata child) {
 
 		final OmeNgffDataset dset = new OmeNgffDataset();
 		// paths are relative to this object
-		try {
-			dset.path = N5URI.normalizeGroupPath(
-					N5URI.from("", getPath(), "").resolve(N5URI.from("", child.getPath(), ""))
-					.getGroupPath());
-		} catch (URISyntaxException e) { }
-
+		dset.path = MetadataUtils.relativePath(getPath(), child.getPath());
 		dset.coordinateTransformations = child.getCoordinateTransformations();
 		if (idx < 0)
 		{

src/test/java/org/janelia/saalfeldlab/n5/universe/metadata/ome/ngff/v04/BuildMultiscaleTest.java

@@ -2,6 +2,7 @@
 
 import static org.junit.Assert.assertEquals;
 
+import org.janelia.saalfeldlab.n5.N5URI;
 import org.janelia.saalfeldlab.n5.universe.metadata.axes.Axis;
 import org.janelia.saalfeldlab.n5.universe.metadata.axes.AxisUtils;
 import org.junit.Test;
@@ -40,6 +41,16 @@ private static void testHelper(final String path, final String[] childPaths) {
 		for (int i = 0; i < childPaths.length; i++) {
 			assertEquals(childPaths[i], meta.getDatasets()[i].path);
 		}
+
+		// test building children from multiscales
+		// these metadata's path variables must be relative to the root
+		final NgffSingleScaleAxesMetadata[] children = OmeNgffMultiScaleMetadata.buildMetadata(3, path, null, meta);
+		for (int i = 0; i < childPaths.length; i++) {
+			// ensure the paths are equal up to normalization
+			assertEquals(
+				N5URI.normalizeGroupPath(path + "/" + childPaths[i]),
+				N5URI.normalizeGroupPath(children[i].getPath()));
+		}
 	}
 
 	private static NgffSingleScaleAxesMetadata buildScaleLevelMetadata(final String path, final double[] res,