FAQ OpenEuclide

OpenEuclide is a plane geometry software. It can produce exact figures. A figure is built by adding objects one by one.

Here are some questions/answers making a brief tour of OpenEuclide's features.

• How do I force OpenEuclide to speak English ?
  If either your OpenEuclide speaks french, just go to the Menu [Fichier/Langage] and click on 'anglais'. Restart OpenEuclide.
• There is nothing on my sheet ! How do I begin ??
  As an example, create a free point, that is, a point that can be moved by the mouse. For this, click on the button [free point], then click anywhere on the sheet.
• How can I build a triangle in just two clicks ?
  Feel lucky, triangles are in the list of "compound objects" that OpenEuclide can build automatically for you. Click on the button "triangle", then click anywhere on the sheet. Indeed, instead of clicking, you can drag a region with the mouse by letting the left button down. Then the coumpound object is built so that it fits the region.
• How do I create an object, say the middle of two points ?
  Imagine we have built a triangle ABC according to last question. Click on the button [middle], then click on two existing points, say A and B. The middle of (A,B) appears. If either you clicked on an empty place of the sheet instead of an existing point, then a new point has been automatically created at this place.
• How do I give names to my new objects ?
  You can give names to objects, either on 1 or 2 letters. To give a name to an object with no name, click on it so that it is selected, then tape its name. You can also double-click on an object to access its properties.
• How to destroy an object ?
  Select it and hit [del], or go to the menu [Edit/Delete]. Be careful ! if some other objects were directly or indirectly defined according to the one you delete, they are deleted too. You can always cancel an action, like deletion, by pressing [Ctrl+Z].
• Why is the purpose of the "hide" function ?
  You're right, there is a [hide] function in the [Edit] menu. Any object can be hidden by selecting it and pressing [Ctrl+H]. The object disappears from the sheet, but it still exists. This is useful for "cleaning" the sheet from some meaningless objects that are just intermediates and you don't want them to appear. Compare documents [commonTangents.ecl] and [commonTangentsClean.ecl], which are identical, except that some intermediate stuff has been hidden.
• What is the purpose of labels, and how do I move them ?
  A label is a text zone on the sheet. It can be a comment written by you (try the "comment area" button). Some geometric objects are themselves labels, like length measures. You can position labels by sliding them with the mouse. To prevent an overload of active regions on the sheet, the region of a label that reacts to the mouse is at the top-left of it (where you see a corner).
• What does the object "length measure" really measures ?
  The object "length measure" gives the distance between two points. Whatever, the notion of "length" is rather relative on a screen. At the beginning, all is simple: your sheet's width is 2. But you can define a "unit length", that is a length that is defined to equal 1. All other measures will depend on it. For this, create a length measure, and double-click on it (the left side of the label). The property dialog is opening. Click on the button "Set this length as unit".