Re: [Inkscape-user] Inkscape Accuracy
Shawn,
I think we all understand that the problem you're addressing is a serious one. Inkscape will render older images based on 90ppi at a smaller size when it changes its definition for pixels per unit.
Since there had been discussion of absolute size in the thread, I thought that the conversions might be of interest to those who might have a project that requires absolute sizing, even though it is of no help to you. <snif>
And thanks for the heads up about 2.54cm/inch. I've been using some sewing books which make recommendations of rounding to the 10th rather than 100th perhaps because they were using pencil & paper, and it worked well enough for them personally. This is ultimately garbage advice, so thanks for pointing that out.
Question: Are there differences between Inkscape and other tools regarding pixels per inch?
- Susan
Date: Wed, 12 Jan 2011 08:57:09 -0500 From: Shawn H Corey <shawnhcorey@...155...> Subject: Re: [Inkscape-user] Inkscape Accuracy
Conversion is not the problem. The problem is that the number of pixels per inch keeps changing. It's currently 90, schedule to change to 96, and may change again. That means that old SVGs will become 7% smaller when the new scale is implemented. And that's *all* the old ones since Inkscape stores their measurements as pixels.
BTW, it's 2.54 cm per inch. :)
-- Just my 0.00000002 million dollars worth, Shawn
On 11-01-12 10:44 PM, Susan Spencer wrote:
And thanks for the heads up about 2.54cm/inch. I've been using some sewing books which make recommendations of rounding to the 10th rather than 100th perhaps because they were using pencil& paper, and it worked well enough for them personally. This is ultimately garbage advice, so thanks for pointing that out.
It's not that the advise is complete garbage, it depends on what you want. It's just that you had 1 in = 72.72 pts, which is 4 significant digits and 1 in = 2.5 cm, which has only two. It's best to have the same number of significant digits for all your conversions. :)
On Thu, Jan 13, 2011 at 09:12:56AM -0500, Shawn H Corey wrote:
On 11-01-12 10:44 PM, Susan Spencer wrote:
And thanks for the heads up about 2.54cm/inch. I've been using some sewing books which make recommendations of rounding to the 10th rather than 100th perhaps because they were using pencil& paper, and it worked well enough for them personally. This is ultimately garbage advice, so thanks for pointing that out.
It's not that the advise is complete garbage, it depends on what you want. It's just that you had 1 in = 72.72 pts, which is 4 significant digits and 1 in = 2.5 cm, which has only two. It's best to have the same number of significant digits for all your conversions. :)
I've once been told that the US is legally on the metric system and that the inch is *defined* to be 2.54 cm., which makes 2.54 exact to as many decimal places as you want. I'd like to know if this is actually true. Anybody know?
-- hendrik
On 11-01-13 01:47 PM, Hendrik Boom wrote:
I've once been told that the US is legally on the metric system and that the inch is*defined* to be 2.54 cm., which makes 2.54 exact to as many decimal places as you want. I'd like to know if this is actually true. Anybody know?
FYI:
I been digging around and the best I can determine is:
1.0000 in = 2.5400 cm
Absolutely true. 1 inch is exactly 2.54 cm by definition/convention.
-----Original Message----- From: Shawn H Corey [mailto:shawnhcorey@...155...] Sent: Thursday, January 13, 2011 12:06 PM To: inkscape-user@lists.sourceforge.net Subject: Re: [Inkscape-user] Inkscape Accuracy
On 11-01-13 01:47 PM, Hendrik Boom wrote:
I've once been told that the US is legally on the metric system and
that
the inch is*defined* to be 2.54 cm., which makes 2.54 exact to as
many
decimal places as you want. I'd like to know if this is actually
true.
Anybody know?
FYI:
I been digging around and the best I can determine is:
1.0000 in = 2.5400 cm
On Thursday 13 January 2011 13:47:34 Hendrik Boom wrote:
On Thu, Jan 13, 2011 at 09:12:56AM -0500, Shawn H Corey wrote:
On 11-01-12 10:44 PM, Susan Spencer wrote:
And thanks for the heads up about 2.54cm/inch. I've been using some sewing books which make recommendations of rounding to
the
10th rather than 100th perhaps because they were using pencil& paper, and it worked well enough for them personally. This is ultimately garbage advice, so thanks for pointing that out.
It's not that the advise is complete garbage, it depends on what you want. It's just that you had 1 in = 72.72 pts, which is 4 significant digits and 1 in = 2.5 cm, which has only two. It's best to have the same number of significant digits for all your conversions. :)
I've once been told that the US is legally on the metric system and that the inch is *defined* to be 2.54 cm., which makes 2.54 exact to as many decimal places as you want. I'd like to know if this is actually true. Anybody know?
-- hendrik
That's the definition in all my (old) textbooks, like the Chemical Rubber Company's "Abridged Math Tables" of 1964. But TeX has a definition of a printer's point that antedates our current standard of 72 per inch. The TeX definition is 72.27 per inch. Apparently Adobe established the newer standard. Tex calls the Adobe point a "big point" (bp).
"JC" == John Culleton <john@...1668...> writes:
JC> The TeX definition [of a printer's point] is 72.27 per inch.
Knuth writes in the /TeXBook/ that 72.27 is an approximation.
-JimC
"HB" == Hendrik Boom <hendrik@...2611...> writes:
HB> I've once been told that the US is legally on the metric system and that HB> the inch is *defined* to be 2.54 cm., which makes 2.54 exact to as many HB> decimal places as you want. I'd like to know if this is actually true. HB> Anybody know?
Back in the 1950's the, IIRC, SI got annoyed that the inch/foot/mile system and SI were connected by the specification that:
1 metre == 39.37 inch
They felt that that made it look like the inch was the base standard and that the metre were defined by it.
So they inverted the conversion and rounded it so that:
1 foot == 0.3048 metres 1 inch == 2.54 centimetres
The new 2.54cm inch is formally the international inch.
The old 100/3937m inch is the (rarely used) US inch. The corresponding 1200/3937m foot is the US or survey foot, still used for land surveys, often as decimal feet (10.5 ft instead of 10ft 6in).
On the scale of a page of paper, the rounding is negligible. On the scale of a State-wide survey, it would be /very/ noticeable.
The US has at least signed and probably ratified a treaty which does require that everything be metric, but that never seems to be enforced on the States, Territories or Possessions and is usually poorly implemented by the Feds, too. (They write things like:
200 gallons (757.08236 Litres)
instead of rounding the conversion to match.)
Whether the inch to mtre conversion has ever been codified in law, though, I couldn't guess.
-JimC
On 11-01-14 05:45 PM, James Cloos wrote:
Back in the 1950's the, IIRC, SI got annoyed that the inch/foot/mile system and SI were connected by the specification that:
1 metre == 39.37 inch
Using this number:
1 in = 2.54000508001016 cm
-----Original Message----- From: Susan Spencer [mailto:susan.spencer@...155...] Sent: Thursday, January 13, 2011 04:44 To: inkscape-user@lists.sourceforge.net Subject: Re: [Inkscape-user] Inkscape Accuracy
Since there had been discussion of absolute size in the thread, I thought that the conversions might be of interest to those who might have a project that requires absolute sizing, even though it is of no help to you. <snif>
Thanks for adding weigth to the argument!
:-) Johan
participants (7)
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unknown＠example.com -
Hendrik Boom -
James Cloos -
John Culleton -
Jon Bertrand -
Shawn H Corey -
Susan Spencer