My Math Forum Check whether two points are symmetrics/asymmetrics

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 July 26th, 2019, 10:53 AM #1 Newbie   Joined: Jul 2019 From: Culadnia Posts: 1 Thanks: 0 Check whether two points are symmetrics/asymmetrics I'm working on an Android app that lets a group of children draw whatever they want in a specific area. I need to check whether the lines and figure that they draw are symmetric. The problem is that since the app is designed to let them draw freehand, I don't know how to compare the lines by considering a certain flexibility. For example, I would consider symmetric these two "triangles" in the image: even if they have not the same inclination and the same length. Do you have any suggestion? These are the points of the two shapes, do you notice any constant or something similar I can use to find what I need? Triangle on the top: 1303.9062, 245.88171 1306.9531, 239.48767 1309.055, 234.89392 1309.9219, 231.82782 1312.2241, 231.00659 1312.8906, 228.64291 1312.8906, 226.54477 1315.9375, 227.98535 1315.9375, 231.00659 1319.2817, 236.99414 1319.9219, 243.00916 1322.1042, 244.02539 1322.8906, 248.47485 1322.8906, 251.52356 1322.8906, 255.54462 1324.9263, 256.98926 1325.9375, 260.74615 1325.9375, 265.4226 1325.9375, 267.45148 1325.9375, 269.0193 1330.1698, 269.0193 1328.9062, 275.0343 1328.9062, 275.9956 1328.9062, 279.01685 1328.9062, 281.98315 1331.9531, 285.0044 1331.9531, 285.0044 Triangle in the bottom: 1133.9062, 950.9956 1133.9062, 955.37256 1136.1552, 959.9429 1136.9531, 965.0901 1138.6583, 968.71606 1139.9219, 972.3617 1142.586, 976.9783 1143.9062, 982.42285 1146.608, 985.6449 1146.9531, 990.5189 1149.9219, 999.83105 1149.9219, 1002.55286 1153.7056, 1005.82275 1152.8906, 1010.1306 1154.862, 1011.9697 1155.9375, 1016.5016 1155.9375, 1018.0122 1155.9375, 1020.9785 1155.9375, 1024.9885 1159.9219, 1024.9885 1163.43, 1017.47314 1162.8906, 1013.48035 1165.9375, 1008.792 1167.0302, 1000.8804 1168.9062, 995.6416 1171.9531, 990.8357 1175.2189, 986.532 1175.9375, 981.4552 1178.9062, 975.46765 1181.9531, 970.21094 1181.9531, 966.84827 1186.4062, 966.9807 1184.9219, 962.5906 1184.9219, 960.99316 1187.8906, 960.99316 1187.8906, 956.98315 1187.8906, 956.98315 Last edited by skipjack; July 27th, 2019 at 10:24 AM.
 July 28th, 2019, 08:17 AM #2 Senior Member     Joined: Sep 2015 From: USA Posts: 2,590 Thanks: 1434 What does your input data look like? This in general is a very difficult problem.
 July 28th, 2019, 09:48 AM #3 Senior Member   Joined: Jun 2019 From: USA Posts: 314 Thanks: 165 It does seem quite ambitious. On the other hand, touch screens have been around so long that there has to be a lot of work publicly available that can get you a large portion of the way without having to start from scratch. You might search AI forums or journals for shape recognition algorithms. My guess is there are already librairies for generating simple polylines, and from there it would be easier to define a "similarity" (or "discrepancy") function.

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