René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: offset in transformed ellipse vertices","articleBody":"### Bug summary\n\nI was following [this](https://matplotlib.org/stable/gallery/statistics/confidence_ellipse.html)sexample on drawing ellipses and wanted to get the vertices out. Calling Ellipse.get_vertices() returns the untransformed vertices which may be intended behaviour, but I also seem to be unable to produce the correct vertices under the transform and they seem to be off by a scale factor. Not entirely sure if it's a bug or something I don't understand.\n\nThe following code is a MWE trimmed down from the linked example\n\n\n### Code for reproduction\n\n```Python\nimport matplotlib.pyplot as plt\nfrom matplotlib.patches import Ellipse\nimport matplotlib.transforms as transforms\n\nfig, ax = plt.subplots(figsize=(6, 6))\n\nellipse = Ellipse((0, 0), width=1.15*2, height=2*0.823)\ntransf = transforms.Affine2D() \\\n        .rotate_deg(45) \\\n        .scale(2.54, 1.94) \\\n        .translate(3.64, 4.0)\nellipse.set_transform(transf + ax.transData)\nax.add_patch(ellipse)\n\nvertices = ellipse.get_vertices()\ntransformed_vertices = ellipse.get_transform().transform(vertices)\ndata_verts = ax.transData.inverted().transform(transformed_vertices)\n\nax.plot([vertices[0][0],vertices[1][0]],[vertices[0][1],vertices[1][1]],c='green')\nax.plot([data_verts[0][0],data_verts[1][0]],[data_verts[0][1],data_verts[1][1]],c='red')\n\nplt.savefig('ellipse_test.png')\nplt.show()\n```\n\n### Actual outcome\n\n![Image](https://github.com/user-attachments/assets/b1cabc9d-db6a-4df1-9d1d-db1bdf287684)\n\n### Expected outcome\n\nThe red line to have endpoints associated with the vertices of the ellipse\n\n### Additional information\n\n_No response_\n\n### Operating system\n\nUbuntu\n\n### Matplotlib Version\n\n3.10.3\n\n### Matplotlib Backend\n\n_No response_\n\n### Python version\n\n_No response_\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nNone","author":{"url":"https://github.com/calebmiller","@type":"Person","name":"calebmiller"},"datePublished":"2025-06-11T14:03:43.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/30165/matplotlib/issues/30165"}