Re: Difficulty with createLine

[Juan Pablo Carbajal]

On Thu, Jun 2, 2016 at 10:41 PM, Thomas D. Dean <address@hidden> wrote:
> I have two scripts that create lines, using the same data, but different
> calls and I get different lines when I think I should be getting the same
> line.
>
> The first set of data comes from a complicated calculation.
>
> octave:1027> relTgtPosit
> relTgtPosit =
>
>    95.0000   16.0000
>    80.2279   -3.8953
>    65.4558  -23.7906
>    53.4611  -31.3488
>    29.4717  -46.4653
>     5.4823  -61.5818
> relTgtLeg =
> createLine([relTgtPosit(1,:),relTgtPosit(3,:);relTgtPosit(3,:),relTgtPosit(6,:)])
>
> The second set of data comes from direct assignment
>
> T1 = [95.0000   16.0000]
> T2 = [80.2279   -3.8953]
> T3 = [65.4558  -23.7906]
> lineT = createLine(T1,T3);
>
> figure; hold on; axis([0 120 -80 20]);
> grid
> drawLine(relTgtLeg(1,:), 'color', 'b')
> drawLine(lineT, 'color', 'c')
> hold off
>
> I think the two lines, relTgtLeg(1,:) and lineT should be the same.
>
> What am I doing wrong?
>
> Tom Dean
>
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I think you need to read the help of createLine carefully, I cite:

L = createLine(LINE); where LINE is an array of 4 values, creates
     the line going through the point (LINE(1) LINE(2)), and with
     direction given by vector (LINE(3) LINE(4)).

This is what you are using to build relTgLeg(1,:). So the lines goes
through [95, 16] with direction [65.4558 , -23.7906]
For lineT you use

 L = createLine(p1, p2); Returns the line going through the two
     given points.

so a line that goes thought [95, 16] and [65.4558 , -23.7906]. Thse
two are clearly not the same line. You can create lineT doing

lineT = createLine([T1,T3]);

and you will get the same line as relTgLeg(1,:).