Extension Lines#

With some dimensions, such as inner, start and end on the vessel wall, it is obvious what they are measuring, but there other dimensions drawn outside of the vessel where the actual measuring point has to be explicitly shown. Use extension lines to aid the user. Generally these are perpendicular to both the object (vessel wall) and the dimension line.

Using an outer vertical dimension as an example, the vessel wall is shown as a thick blue line running vertically. The dimension, also vertical, will show the length of the vessel, and lie to the left of the vessel wall. The extenders will lie horizontal and show to which points on the wall the dimension is referring.

The extender almost touches the vessel wall, but intersects the dimension and extends slightly past it.

On a dimension that is always vertical or horizontal one could calculate the dimension and extender positions using two dictionaries with the sine and cosine values of the relevant horizontal and vertical angles:

sin0 = {-180: 0, -90: -1, 0: 0, 90: 1, 180: 0, 270: -1, 360: 0}
cos0 = {-180: -1, -90: 0, 0: 1, 90: 0, 180: -1, 270: 0, 360: 1}

then calculate the next position with something like this:

ptC = ptA[0] + abs(extaO) * cos0[angle-90], ptA[1] + abs(extaO) * sin0[angle-90]

One could equally have used the sine and cosine values directly:

ptC = ptA[0] + abs(extaO) * cos(angle-90), ptA[1] + abs(extaO) * sin(angle-90)

The problem is that the values are real numbers and some parts of the program require integers. When using the dictionaries this problem falls away.

In the end the function polar2cart was used, since the splitting of the points into x and y coordinates, and providing integers for the result was already taken care of:

ptC = polar2cart(ptA, angle-90, abs(extaO))

Extension Lines#

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