Imperial scale for printing/export

[Eric C. Landgraf]

Currently, printing scales for aven's print dialogue are a series of static values, and a magic "fit to page". As an american, I usually sketch underground at "odd" scales: 1:240, 1:300, 1:480, and 1:600 (inch to 20, 25, 40, and 50 feet, respectively). If I want to e.g. plot on a printout, the math gets very difficult with US-units survey. It probably doesn't make sense to add these scales to the list of options, though. A solution to this problem would be "custom" print scales.

[Olly Betts]

You can already do this - just click on the scale number and type in 240 or whatever you want.

For convenience we could provide an alternative standard list and a metric scales checkbox to switch between them, or something like that.

Or perhaps just add the imperial scales to the standard list.

[Olly Betts]

No further comments, but not sure if I should regard this as resolved or not. The requested custom scales are already supported, though it seems some sort of clearer UI clue that this is possible might be helpful. Currently the mouse cursor changes to a I-beam when moved over it, but we could add a pop up hint on mouse over.

If there are a common set of "imperial scales" that would be more useful to a US caver than the current list of scales I can add an alternative list and a way to toggle between them (it could default automatically based on whether metric is on for length units).

However I need to be given a suitable list in order to do that as I've little idea what non-metric scales are appropriate.

[Eric C. Landgraf]

the US scales I've seen used would be (in order of commonality) 1":20' (1:240), 1":50' (1:600), 1":40', (1:480), 1":25' (1:300), and 1mm:1ft (1:301).

Having shortcuts for at least 1":20' and the UI tweak to make custom scales obvious would both help.

[Olly Betts]

For now I've added a ... entry to the end of the list - selecting this clears the value and gives focus to the text entry part of the control.

I think a custom list of scales makes sense, but it seems it ideally should show things like 240 (1":20') or 301 (1mm:1ft) rather than just the raw numbers. I think that will need some more significant code restructuring to work well, but I really need to get a release out so I can update the Debian package before Debian freezes.

Shouldn't it 1:304.8 for 1mm:1ft though? That's the conversion factor Survex uses, which is the international definition of the foot according to ​https://en.wikipedia.org/wiki/Foot_(unit) - I guess you may actually be using the US survey foot, but that would also be 304.8 to 2 decimal places.

(Maybe Survex should directly support the US survey foot as a unit. It's only different by 1 part in ~500,000 which is so far below the accuracies we're dealing with in cave survey data that it seems irrelevant, but it is a systematic error and I can understand some people may want to eliminate it. Currently you'd have to use *units length 0.3048006096012192 meters or something like that.)

[Eric C. Landgraf]

you're right about mm:ft. I'd incorrectly memorised that conversion factor (it's so close to 1:300 that I treat mm:ft as interchangable with 1in:25ft, but I knew it was off a tiny bit).

I think survey foot is an inconsequential error. American's rarely read their tape to the nearest cm (usually read to the nearest 5/100th of a foot, which is about 1.5cm...), although newer disto surveys, some people will record 2 decimal places.