I have a printed map of a district with several points on it that can be used as geolocation reference points.

I have the shapefile of this map in QGIS. If someone draws a point on the printed map, how can I find the position of the drawn point without scanning the printed map ?

I was thinking of measuring the distance from that point to three other points on the paper, so I can have the zoom used and find the position. Is there a plugin to help with that? Are there other ways to accomplish this?

  • This is essentially a math problem. See this answer: math.stackexchange.com/a/100456 you could probably do something in Python to solve this. – Jesse McMillan Jan 29 '17 at 6:22
  • Thanks. If I take the formulas in this answer, can I replace x,y with latitude and longitude or is there a transformation to make using the projection ? Considering that it is the map of a district it is at an important level of zoom and I need a precision at around 50m. – syldor Jan 29 '17 at 6:38
  • you should be able to plug in your latitude and longitude. Keep in mind latitude is Y and longitude is X so it's the reverse of how we usually think of things. – Jesse McMillan Jan 29 '17 at 18:56

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