Methods of centroid determination in QGIS – proposal of an algorithm using the “Model Designer” tool

The article talks about determination of centroids. The introduction outlines a number of definitions of centroids. Then, various methods of their determination and example applications are discussed. The paper also describes algorithms of calculation of centroid coordinates implemented in QGIS. Then, with the use of the model designer tool, an algorithm was developed to determine centroids on a reference surface, followed by calculations in QGIS. We calculated the coordinates of selected polygons on a surface in the systems PL-1992, PL-LAEA and PL-LCC, as well as on the GRS80 ellipsoid, Krasowski ellipsoid and on a sphere. The test area was Poland in its administrative borders, including territorial waters. The paper is concluded with an analysis and comparison of the obtained results.