BasicGeometricCalc Intersect_​circle_​line bad results

[John Peterson]

I’ve been starting to use the geometric calculator for GDL scripts. My first attempt worked great for finding the intersection of two circles.

My next attempt at finding the intersection of a line and a circle does not work. The line starts at .5,0 and the vector directional point is .5,1. The circle center points are 0,0 and the radius is 1.5. Below, you can see I have drawn the circle, the line, and had the calculator provide the two intersection points. It’s a bit hard to see, but they hotspots do not fall on the circle as they should. I’m using 22 but have not installed the latest patch that just became available last week. Haven’t had time to comb through the release notes. Snip of the code is below.

(from master script) INTERSECT_CIRCLE_LINE = 5

(from 2d script)

line2 .5, 0, .5, 1
circle2 0, 0, 1.5

call “BasicGeometricCalc” PARAMETERS iFunction=INTERSECT_CIRCLE_LINE,
xo=0,
yo=0,
ro=1.5,
linePx=.5,
linePy=0,
lineVx=.5,
lineVy=1,
RETURNED_PARAMETERS ipx1,ipy1,ipx2,ipy2,state

if state=2 then
hotspot2 ipx1,ipy1
hotspot2 ipx2,ipy2
endif

if state=1 then
hotspot2 ipx1,ipy1
endif

Attachments:

1. 

   line-circle-intersection.jpg
   

Many thanks, JP

[Lingwisyer GC]

I have never used it, but is it suppose to work with line extensions? Even if the return is that your lines do not intersect.

Ling.

Edit: Ah. Reading the documentation it is circle to vector, so it is suppose to work.

AC18-23 AUS 4006
Self-taught, bend it till it breaks.
Win7 | E5620 x 2 | 24GB | K2200

[Lingwisyer GC]

Is there any change if your line is not orthogonal?

AC18-23 AUS 4006
Self-taught, bend it till it breaks.
Win7 | E5620 x 2 | 24GB | K2200

[Péter Baksa]

Hi,

each input “direction vector” of BasicGeometricCalc has to be a unit vector (length = 1.0 meter). You get a unit vector by dividing each coordinate with the length.
The returned vectors are unit vectors too.

Péter Baksa
Library Platform, Software Engineer
GRAPHISOFT SE

[John Peterson]

I did make my vector exactly 1 meter from the reference point. It obviously does not work, and if the input needs to be something else that involves extra math, that’s just plain stupid.

Many thanks, JP

[Péter Baksa]

Hi John,

The vector is not the endpoint of the vector, just the vector itself. So in your case if (0.5, 0) and (0.5, 1) are two points on the line, the vector is (0, 1).

BasicGeometricCalc can return the unit vector between two points:

call "BasicGeometricCalc" parameters iFunction = 1,
                                      Point1X = toX,   Point1Y = toY,   Point1Z = toZ,
                                      Point2X = fromX, Point2Y = fromY, Point2Z = fromZ,
                  returned_parameters Vx, Vy, Vz, distance

Vx, Vy, Vz will be the unit vector, and distance will be the distance between Point1 and Point2.

Péter Baksa
Library Platform, Software Engineer
GRAPHISOFT SE

[John Peterson]

Thank you Peter!! That is exactly it. Thanks for taking the time to set me straight.

Many thanks, JP

Many thanks, JP

[John Peterson]

Good morning Peter! May I impose upon you again for an explanation? I’m now using the DIRECTION_SEGMENT function because I can’t use a curve in a tube path. I have the start, end, and included angle of the arc segment as shown in the diagram. I provided a tolerance. I used vardim1 to see how many items were in the array. The result was 6. I followed the instructions to find the various x,y coordinates. The resulting points are nowhere near to points on that curve, or the curve inverted. They don’t have any reference to the curve whatsoever. What i did notice as the distance from the origin to point one and the same to point two was exactly 1 meter. The distance to the third point was not. Can you offer a bit of advice please?

Strike that. I found the problem. The code is wrong on the website. It lists DIRECTION_SEGMENT as the function. The name sounded funny to me so i refereed to the index and there was one that made a lot more sense called SEGMENT_ARC. That worked perfectly. Can you please alert someone as to the error and also please tell them to make the pictures larger and more legible. They are almost impossible to read.

Many thanks, JP

[Péter Baksa]

Thank you, Using BasicGeometricCalc macro is updated with clickable image links.

Péter Baksa
Library Platform, Software Engineer
GRAPHISOFT SE

[Author]

Posts