# Bricscad Python

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Background information about B-spline at Wikipedia.

## Splines from fit points¶

Splines can be defined by fit points only, this means the curve goes through all given fit points.AutoCAD and BricsCAD generates required control points and knot values by itself, if only fit pointsare present.

Create a simple spline:

- Spend the next month, I mean 8 hours a day, every single day on top of your job, learning the free 30 day demo of Bricscad and python programming. Then contact me again and I will hook you up with a way to run Python scripts in Bricscad through the open source, Python to.NET interpreter software called IronPyhon.
- Commands: PEDIT and PEDITEXT The Edit vertices option of the Pedit command modifies individual polyline vertices. When you select this option, the program switches into a special vertex editing mode and places an X on the first vertex.
- Bricsys website.

### Bricscad Python Tutorial

Append a fit point to a spline:

You can set additional control points, but if they do not fit the auto-generated AutoCAD values, they will be ignoredand don’t mess around with knot values.

Solve problems of incorrect values after editing a spline generated by AutoCAD:

As far as I have tested, this approach works without complaints from AutoCAD, but for the case of problemsremove invalid data:

## Splines by control points¶

To create splines from fit points is the easiest way to create splines, but this method is also the least accurate,because a spline is defined by control points and knot values, which are generated for the case of a definition byfit points, and the worst fact is that for every given set of fit points exist an infinite number of possiblesplines as solution.

AutoCAD (and BricsCAD also) uses an proprietary algorithm to generate control points and knot values from fit points,which differs from the well documented Global Curve Interpolation. Therefore splines generated from fit pointsby ezdxf do not match splines generated by AutoCAD (BricsCAD).

To ensure the same spline geometry for all CAD applications, the spline has to be defined by control points. The method`add_spline_control_frame()`

adds a spline trough fit points by calculating the controlpoints by the Global Curve Interpolation algorithm. There is also a low level function`ezdxf.math.global_bspline_interpolation()`

which calculates the control points from fit points.

- black curve: AutoCAD/BricsCAD spline generated from fit points
- red curve: spline curve interpolation, “uniform” method
- green curve: spline curve interpolation, “chord” method
- blue curve: spline curve interpolation, “centripetal” method

### Open Spline¶

Add and open (clamped) spline defined by control points with the method`add_open_spline()`

. If no knot values are given, an open uniform knot vector will begenerated. A clamped B-spline starts at the first control point and ends at the last control point.

### Closed Spline¶

A closed spline is continuous closed curve.

### Rational Spline¶

Rational B-splines have a weight for every control point, which can raise or lower the influence of the control point,default weight = `1`

, to lower the influence set a weight < `1`

to raise the influence set a weight > `1`

.The count of weights has to be always equal to the count of control points.

Example to raise the influence of the first control point:

## Spline properties¶

Check if spline is a closed curve or close/open spline, for a closed spline the last point is connected to thefirst point:

Set start- and end tangent for splines defined by fit points:

Get data count as stored in DXF file:

Get data count of real existing data:

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