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From: Rune Allnor <allnor@tele.ntnu.no>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Projection of a point over a line
Date: Thu, 24 Nov 2011 09:46:38 -0800 (PST)
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On 24 Nov, 18:23, "Waleed El-Badry" <wba...@must.edu.eg> wrote:
> Hi,
> I recently created read an algorithm for finding the coordinates of projected point on a line
...
> The problem is the formula only works if the line is horizontal and fail in case of vertical or inclined line !
>
> Do I miss something?

I don't know, as I have no idea how you were
thinking when you wrote that code.

The way to do these kinds of things is to
set up matrix/vector expressions for the
point and the line:

Assume the vector u represents the point and
the vector v represents the line (through origo).

In that case the vector P representing the projected
point is computed as (u and v column vectors)

P = vv'u.

If the line doesn't intersect origo, you need a
modification which is simple if you understood a word
above what I explained above (that is, if you
know linear algebra), and rather uncomprehensable
if not.

Rune