bow-simulation
Make the definition of the brace height and draw length adjustable
Brace height and draw length are measured against the coordinate origin (red). The position of the origin relative to the bow limb is determined by the handle geometry, i.e. length, setback and angle. Currently with the profile curve as the reference, which lies at the back of the bow.
Instead, define the handle length and setback relative to the edge of the limb as shown below. This way, the brace height and draw length are measured w.r.t. the belly side of the bow/grip by default, i.e. when handle length and setback are zero. This is the more usual convention as opposed to measuring against the back.
Even when handle length and setback are not zero, i.e. when the bow has a riser, this definition makes more sense because the reference point is actually a geometrical point on the riser, where the limb attaches.
Please make possible to use AMO standard definition of the draw lenght. So 26,25" from the pivot point + 1,75" = 28" draw length. http://www.outlab.it/doc/amostd.pdf
Hi @Puujousi, have you already tried the new Reference option? I think setting the reference to Belly and the offset to -1.75" should result in the draw length being measured according to AMO.
One remaining problem is that the brace height in VirtualBow is currently always measured from the same reference point as the draw length. I wonder if I should make this configurable too, so that draw length can be measured according to AMO or from the back of the bow while the brace height can be measured from the handle's pivot point as it's usually done.
My current idea is to split "Offset" into "Pivot offset" for defining the bow's pivot point (where the brace height is measured) and a "Draw offset" for defining where the draw length is measured relative to the pivot point. Something like this (riser/no riser):
Still looking for a better name than "draw offset" though...
I think that the current Dimensions → Handle → Reference setting should define the “zero plane” when modelling a bow. For example, if the zero plane is set at the back of the bow, it becomes easier to determine the net reflex, and so on.
Next, there needs to be a clear definition for how the draw length is measured. There are three possibilities: from the back, from the belly (pivot point), or according to the AMO standard. The previously defined zero plane does not affect these parameters—it is only used for modelling. If the AMO standard is selected, then the draw length should be calculated as the draw length from the pivot point + 1.75".
It would be very useful to allow both SI and imperial units in this section, regardless of the selected global unit setting (Options → Units). Using inches for draw length is natural even for “metric” archers, so the draw length should be enterable in either millimetres or inches.
I believe that “Draw offset” and “Pivot offset” are unnecessary parameters. The only offset relevant here is the 1.75" defined by the AMO standard, and it is simpler to specify the AMO draw length directly. The pivot offset is also unnecessary, because no one would use the type of reference point shown in the left image.
When determining brace height and draw length, the only meaningful reference points are the back and belly of the handle. Using the belly is the only unambiguous option, as it always results in the same effective brace height or draw length, regardless of the handle’s shape or dimensions.
Thanks for your input! Interesting point about making the zero plane independent from the draw length definition. I think that might be a good idea. A more fine-grained configuration of units too, of course.
I believe that “Draw offset” and “Pivot offset” are unnecessary parameters. The only offset relevant here is the 1.75" defined by the AMO standard, and it is simpler to specify the AMO draw length directly. The pivot offset is also unnecessary, because no one would use the type of reference point shown in the left image.
I would agree for the case on the right but I'm not sure how this would work for the case on the left, when the middle piece/grip/riser is not modelled in VirtualBow. I'm thinking of bows that look like this in VirtualBow:
So basically just two limbs floating in the air. The belly reference point is just the edge of the limb here. The actual pivot point/deepest point of the grip from where the brace height and draw length are measured sits somewhere on the invisible riser. So I still think there needs to be a way to specify at least the pivot point.
But I see how that complicates bows like that on the right. Maybe it would be best to have a selection on top between "One-piece" and "Riser". And depending on the selection, different inputs:
-
One-Piece
- Reference for brace height is belly -> No input needed
- Reference for draw length is belly too, but input whether "AMO" or "true" draw length is used
-
Riser
- Distance between limbs, i.e. riser length
- Attachment angle of the limbs to the riser
- Position of the pivot point relative to the limb (reference point + offset)
- "AMO" or "true" draw length