Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>There are correct answers already, but I think it might be more generally useful to have a formula that gives the distance of any point from a specified line. Then you can just check if this is zero, or within whatever tolerance you choose. The following should work regardless of special cases like vertical lines (infinite gradient).</p> <p>The distance of point <em>X</em> from the line <em>AB</em> is</p> <p>    <a href="http://hypftier.de/dump/SO-6276361-Ben-1.png" rel="nofollow noreferrer">http://hypftier.de/dump/SO-6276361-Ben-1.png</a></p> <p>where <em>A</em>, <em>B</em> and <em>X</em> are the 3D position vectors of the three points (just set <em>z</em> = 0 if you are only working in 2D) and <em>x</em> is the vector product. That comes to</p> <p>    <a href="http://hypftier.de/dump/SO-6276361-Ben-2.png" rel="nofollow noreferrer">http://hypftier.de/dump/SO-6276361-Ben-2.png</a></p> <p>where <em>A</em> = (a,b), <em>B</em> = (c,d) and <em>X</em> = (x,y). Then to check that the point is actually within the line segment and not elsewhere on the infinite line, you can use the scalar products: the distance of <em>X</em> along the line from <em>A</em> to <em>B</em> is</p> <p>    <a href="http://hypftier.de/dump/SO-6276361-Ben-3.png" rel="nofollow noreferrer">http://hypftier.de/dump/SO-6276361-Ben-3.png</a></p> <p>i.e.</p> <p>    <a href="http://hypftier.de/dump/SO-6276361-Ben-4.png" rel="nofollow noreferrer">http://hypftier.de/dump/SO-6276361-Ben-4.png</a></p> <p>and this should lie between 0 and <a href="http://hypftier.de/dump/SO-6276361-Ben-5.png" rel="nofollow noreferrer">http://hypftier.de/dump/SO-6276361-Ben-5.png</a></p>
    singulars
    1. This table or related slice is empty.
    1. POJava - Is a line stretching from (a,b) to (c,d) touching Point(x,y)?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USBen
    1. USBen
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POJava - Is a line stretching from (a,b) to (c,d) touching Point(x,y)?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COOh, right. That one I totally forgot. And with a little leeway it should work acceptably for pixels on screen as well (where the points won't be *exactly* on the line, I guess).
      singulars
      1. PO
      1. USJoey
    2. COThanks Joey for the formula images.
      singulars
      1. PO
      1. USBen
    3. COHi @Ben (or @Joey), can you confirm that the above equation is based on...Point X is (x, y) and Line AB is a line from (a,b) to (c,d)? Thanks
      singulars
      1. PO
      1. USrog8gm
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload