error with returned angle by orientedMinimumBoundingBox()

[300000kms]

in qgis3.4 and ubuntu16
with geometries projected in 25831
the angle obtained by the function orientedMinimumBoundingBox is not the same as the obtained using the function angleBetweenThreePoints
And this second is the correct

oriented minimum bounding box

geom, area, angle, width, height = z.geometry().orientedMinimumBoundingBox()

angle manually calculated

a = math.degrees(QgsGeometryUtils.angleBetweenThreePoints(
geom.vertexAt(0).x(),geom.vertexAt(0).y(),
geom.vertexAt(1).x(),geom.vertexAt(1).y(),
geom.vertexAt(1).x(),geom.vertexAt(1).y()+1000000,
))

a != angle
a != angle-180

[lbartoletti]

@300000kms QgsGeometryUtils.angleBetweenThreePoints return an angle in radians. You converted it in degrees, but orientedMinimumBoundingBox() returns an angle in degrees converted from angle in radians clockwise from the north direction.

You can take a look at our test files:
https://github.com/qgis/QGIS/blob/master/python/plugins/processing/tests/testdata/custom/oriented_bbox.gml
https://github.com/qgis/QGIS/blob/master/python/plugins/processing/tests/testdata/expected/oriented_bounds.gml