# A point dependent on multiple conditions.

Forest_roby shared this question 10 years ago

Hi,

This is the first time I am using this program so it is probably not surprising that I am here.

I try to make a transformation from front and top view of a 3d object. Lot's of lines and points.

Can I set a point on such a way that it is going to be dependent on multiple conditions?

Like I want C point on e line and I want C point to be a specific distance from D point ( D also on e line ) and that specific distance is the distance between A and B not on e line. Now there is two possible C but I want only one.

So when I move e line or change the distance between A and B, C will change accordingly.

Is this understandable ?

English is not my first language. I hope this made some sense.

2

If you could post a copy of your file, it will be easier for us to see what you are discussing...possibility of quicker answers...any assist you provide with questions is a great help to willing assistance, but you help will help us...

Welcome to GeoGebra...

Tony

1

Hi, and welcome to the forum!

First: GeoGebra 4.0 and 4.2 (which will be released shortly) are 2D-programs, but with a bit of thinking you can make things look like 3D-objects and projections of 3D-objects. Version 5.0 is still in early beta byt has true 3D capabilities with automatic projections, 3D-points etc. If you want to consider this, then look at http://www.geogebra.org/for...

Second: To create a point on a line at a certain distance from another point remember what geometric figure have distance as its main defining feature: the circle.

So I would create a segment between A and B. This results in a variable whose value you can use, say it's called f. Then create a circle with center C and radius f. There is a tool for this, or you can type the command

Circle[A, f]

Then find the intersection points of this circle (call it g) with the line e. Again there is a tool for this, among the point tools. Select the tool, then click the circle and the line. This will create both points but you can hide the one you don't want by clicking on the blue marble/button next to the point in the Algebra window.

I hope this helps.

1

Hello,

First, thank you for the answers!

I attached 2 files that may help you to understand what I want to achieve.

On the ggb file, I want G1 to make it fixed on the line and the distance between Q1 G1 should be BP. I can tell that the distance between B and P is one but if the object is tilted than it is harder to tell plus I want it to be automatic. If I change B and P 's distance for some reason I want G1 automatically re-position itself.

Thx

1

Well as I said...

I would create a segment between B and P. This may be hidden if you wish. This results in a variable whose value you can use, say it's called f. Then create a circle with center Q1 and radius f. There is a tool for this, or you can type the command

Code:

Circle[Q1, f]

Then find the intersection points of this circle (call it g) with the line f_1. Again there is a tool for this, among the point tools. Select the tool, then click the circle and the line. This will create both points but you can hide the one you don't want by clicking on the blue marble/button next to the point in the Algebra window.

1

Thank you! I will try!

1

Success!

Thank you for the help!

https://ggbm.at/559121