Re: gEDA-user: coordinate systems [was: pcb crooked traces]

[Phillip Jones <pjones13@xxxxxxxxx>]

On Fri, Oct 15, 2010 at 5:15 PM, Stefan Salewski <mail@xxxxxxxxxxxx> wrote:
> On Fri, 2010-10-15 at 11:54 -0700, Andrew Poelstra wrote:
>
>>
>> The reason for it is that this is generally how drawing canvases work,
>> so from a programmer's perspective, it is simpler to have y pointing down.
>>
>
> WHY?
>

Mainly because that has been the standard at least since Televisions
were invented. The beam in a CRT scans from left-to-right,
top-to-bottom. It's codified in the NTSC standard. So (x,y)=(0,0) is
the upper left corner. Why are CRT's like this? Probably because words
in books are also oriented left-to-right, top-to-bottom. Maybe if the
television had been invented in the middle-east it would be different.
I've got several digital image processing books on my shelf, the
oldest is from 1972. Every one of them defines (x,y)=(0,0) as the
upper left corner of an image. y as positive down, and x as positive
right is simply the de-facto standard in digital image processing.


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