Scale Factor for Acres

[cweinhofer]

I am using Inkscape to make a plot plan for a piece of land. The land is in the US so everything is in feet & acres. I set up the document with a scale of 1 mm = 1 ft.

I would like to use the "Measure Path" tool and have it output the acreage of various polygons, but I am having trouble with the scale factor. After a lot of head scratching I finally figured out that the scale factor needs to be 0.00479 [for anyone reading this later and wanting to know the math, 1 acre equals 43,560 sq ft, which is 208.7 squared. 1 divided by 208.7 equals 0.00479]

The problem is that Inkscape doesn't seem to allow a scale factor lower than 0.1 (it rounds it down to 0.0). I can get part of the way by entering a scale factor of 479.0 and then moving the decimal point in the result by 10 places, but it would be nice if I could get the real number directly.

[Moini]

Perhaps a feature request would be in order?
https://bugs.launchpad.net/inkscape

[brynn]

Welcome to the forum!

Yes, a feature request would be helpful, but doesn't provide a timely solution.

It seems like there ought to be some way to make it work.  My head is kind of swirling with the math right now.  But as long as you're dividing that large of a number into 1, you'll get too small of a result.  So even if you switch to yards (or meters), the result is still way less than 0.1.  Maybe if you set to km?  I'm talking about the units in the Measure Path dialog.

I'm just thinking to set it to something as large as km, might make that conversion factor large enough.  Although I guess it might require an extra calculation somewhere?

If you have the doc set to 1 mm = 1 ft, and you have the area set to sq ft.....  Oh I see.  You want to get the result automatically in acres?  I can't see any other option except to get the result in ft, and then convert the results to acres as a 2nd step.

Well, I can think of a few other ideas, but none of them would be an improvement, and still result in extra calculations.

Oh hey.....  I wonder if there would be any way to use this extension for your project -- somehow or other?  https://inkscape.org/en/~Moini/%E2%98%85realscale-resize-by-line-of-known-length  It doesn't measure area - only length.  I'm just thinking of a land plat as a giant floor plan    Maybe no help at all, but just in case.

I'll volunteer to make that feature request 

Edit - Actually, I wonder if offering acres as a unit would be more effective than changing the allowed Scale Factor?

[cweinhofer]

Thanks for the replys and for putting in the feature request.

Acres as a unit sounds nice, but is it even possible, given acres can only be used as an area unit and not a distance one (all distances in acre calculations use feet). If only the US could get with SI and the rest of the world... 

I think changing the program to having a scale factor that allows for small numbers would be the way to go. It would require the user to know and manually enter the conversion factor, but it would solve the issue in a way that could be useful in a number of other scenarios.

As for a workaround in the meantime, entering a scale factor of 479.0 and then moving the decimal point in the result by 10 places seem to be the best option as it doesn't require an additional calculation, just essentially reformatting.

[brynn]

Made the report:  https://bugs.launchpad.net/inkscape/+bug/1699359

As I noted in the report, I wonder if the problem is more about not allowing more than 1 decimal place.  Because even with higher numbers, it rounds back down to 1 decimal place.  And you have to use at least 2 places to make a number less than 0.1.

Hopefully this will be an easy fix, and won't take too long 

[Lazur]

I am using Inkscape to make a plot plan for a piece of land. The land is in the US so everything is in feet & acres. I set up the document with a scale of 1 mm = 1 ft.

I'd rather set it up as 1 pt :=1 ft
so it's in 1:864
or 2 pt:=1 ft, 1:432
or 3 pt:=1 ft, 1:288 etc.
instead of 1:304.8.

Although I'm not sure about the rest, never had luck with the measurement tool.

[brynn]

(He's using Measure Path extension.)

[Lazur]

The extension?

Well adding more digits to a spinbox shouldn't be a problem at all then.
Had done the same thing with the parametric curves extension myself before.
There it only required to edit the inx file by adding precision="5" after type="float" in the param definitions for five decimal points.

Let's see if I can do the same with the extension in question.

After testing, yes it works.
Open the measure.inx file from inkscape/share/extensions with a text editor, and in the line
<param name="scale" type="float" min="1e-8" max="1e10" _gui-text="Scale Factor (Drawing:Real Length) = 1:">1</param>
insert precision="5" right after type="float".

[brynn]

Wow!  Aside from the fact the op can fix it himself, it's a good sign it might be fixed in the dialog too, since it's so easy.

Personally, I wonder why the Numeric Presicion setting doesn't affect extensions in the first place.  But I guess extensions are are not tied into the base code very closely.

[cweinhofer]

Thanks for all the help brynn & Lazur. That's yet one more great thing about open source software - sometime you can even fix things yourself!

I edited measure.inx as recommended, adding a precision factor of 12 just for good measure (0.004791329788). This will be accurate well beyond  the 4 decimal places that are listed on my county's recorded plot plans.

[brynn]

I had to lol at 12 decimal places