The drawing an elipse with four particular points on the x/y aixs.

Hi,

I've been using this function but have noticed that if you position say your first and second points below the horizontal x axis and then add the other two points when the ellipse is drawn the first two have moved. They don't stay locked exactly in their original locations. For instance if you draw a horizontal line 300mm long at say at -20mm on the y axis then draw the following ellipse using the four sets of coordinates 1st point -100,-20  2nd point 100,-20 3rd point 0,120 and the fourth point at 0,-120 you'll notice that the horizontal line at -20mm doesn't pass through the widest point of the ellipse. The widest point of the ellipse is actually several mm above the horizontal line drawn at what should be the y axis coordinate of first two selected points. The reason I'm trying to get this right is because I'm using it to draw sectionals for an aircraft fuselage where as they move forward towards the nose cone and get smaller the horizontal center line of the fuselage is not the same as the widest part of the aircraft body which actually moves down towards the nose.

Any thoughts as to why these points don't stay locked but seem to move up on the y axis when the ellipse is completed?

Many thanks

Hi Bob,

can you please specify, which LC version you are using.

I haven't completely understood your issue.

When you draw an ellipse with the points (-100,-20) (100,-20) (0,120) (0,-120) the major axis length is 240, exact on the Y axis. The minor axis will be exact on the X axis and must be longer than 200.
The length of 200 will be on a horizontal line at Y -20 or 20, the maximum width is more than 200 at Y 0.

I have drawn this ellipse in LC 2.0.0rc1 and for me it was OK.

Maybe there is a snapping issue?

@dxli
When exploring this issue I found another tolerance issue.
After setting the 3rd point and moving the mouse down, in -Y direction, LC crashed.
I've fixed this with commit 97048dd3

Armin

Hey LordOfBikes and thanks for the very quick response,

I'm using LC version 2.0.0 beta1

What you've done is exactly what I did but what I'm trying to get to is a point where when I enter in the coordinates for the first point of the ellipse which let's say is as per my example of -100,-20 then at the -20 point this stays as the widest point of the final ellipse. The same with the second point or 100,-20. If this was actually the case then the widest point of the whole ellipse horizontally measured would be between the two -20 points. At the moment this isn't the case as as you can see when you complete the ellipse and measure the widest point is at around 0 on the y axis which isn't what I'm trying for.

It may well be that I simply can't achieve what I'm trying to achieve and I'll have to just accept it.

The problem is to get the right overall shape the template in plan view requires the widest point of the fuselage to move down below the horizontal center line or z axis as you move towards the nose and this is why I'm trying to get the widest point to stay at the coordinates I'm measuring and entering for the individual sectionals based on the coordinates from the side and plan view drawings.

It's not too easy to explain on a thread but thanks for trying to help anyway and thanks to Armin for the fix.

Cheers.

OK Bob, that is what I guessed.

What you need is not an ellipse, you need two ellipse arcs. Use the ellipse arc drawing tool.

First draw two construction lines and use snapping on endpoints and intersection or use the command line to enter the coordinates.

1. Line (-100,-20) (100,-20)
2. Line (0,120) (0,-120)
3. Ellipse arc centre(0,-20) major(0,-120) minor(-100,-20) start angle(-100,-20) end angle(100,-20)
4. Ellipse arc centre(0,-20) major(0,120) minor(-100,-20) start angle(100,-20) end angle(-100,-20)

The lower arc is a circle arc in this case, but maybe this changes in another cut and it is safer to use the ellipse arc.

Have fun constructing all the fuselage sections.

Armin

Hey Armin,

I'll give it a try and thanks for the kind assistance.

As regards the fun it's been a long wait. I first started this build back in 1978 when this particular airliner was first put into service but had to scrap it because of marriage, work, living abroad and life and I've had to wait for 35 years until I retired to restart it.

That's why I'm so grateful for your quick responses!!

Cheers and have a great weekend.

Bob

Hey Armin,

Fantastic!!

It works great although it does take my small brain a while to figure out which dimensions/coordinates to enter in as "start angles" and "end angles" etc. as they're obviously not actually a measurement of degrees.

Anyway, I'm getting there - slowly so thanks for all the help.

Regards,

Bob

My pleasure!