The image in the Rider Anatomy tab of the Rider dialogue doesn't provide enough detail to accurately measure a rider.
How should I be measuring a rider - exactly?
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Just to make sure we're on the same page, I assume you are talking about the diagram below:
This stick figure representation can be arrived at in three different ways.
First, you could import a photo of a rider on a bike and match that up with the rider in the BikeCAD model as described at: bikecad.ca/import_photo.
Second, you could measure the rider using the six, more basic, body dimensions in the Fit advisor. You could then use the Fit advisor to approximate values for these more detailed dimensions. This is described at: bikecad.ca/rider_anatomy_tabs.
The third option is to measure the body directly. You would need to use your own judgement to measure as closely to the center of each joint as possible. Of course, the joints of the human body are not simple pin joints as they are depicted here, so this is inherently an approximation.
Regardless of how the dimensions for this rider model are obtained, BikeCAD does not in any way change the model of the bicycle based on the dimensions of the rider model. If you want BikeCAD to change the bike based on the dimensions of the rider, that is done in the Fit advisor. In the case of this particular rider model, the rider is only there to assist you in applying your own judgements in making modifications to the bicycle. Therefore, it is fitting that you are using your own judgment in creating the rider model as well.
I want my measurements to be as accurate as possible with little or no estimation which is why Fit Advisor is not useful. I will use joint locations as suggested but that still leaves a few questions:
1) What are the start and end points for the NK measurement?
2) Should L3 + L2 + L1 + TR = distance from floor to sternal notch when the rider is standing?
3) is A2 from the elbow to the wrist joint? Or is it from elbow to the hand grip?
4) What is PD and how do I measure it? What impact does it have on the rider model?
The base of NK is located at the top of TR. This is the point along the torso where the shoulders attach. The shoulders will not typically be shown right at this point because we also have dimension SR which accounts for the shoulders rolling forward from this point. The top of NK is located at the back of the jawbone.
If we do assume that each of the joints in the body is a pin joint, we could assume that dimensions would add up as you suggest. However, you would need to take one more dimension into account. This has to do with your fourth question, the one about dimension PD. The dimensions AD, ED and KD have no impact on how far the body can reach or stretch out. They are merely there to give what is essentially a stick figure a little more realism. Dimension PD is similar; it is correlated to the size of the pelvis and the size of the upper thigh. However, it will also affect the height of the rider when stretched out. PD defines the diameter of a circle that rests upon the top of the saddle. The base of dimension TR is located at the center of this circle. Therefore, if you were to create a formula to predict the height of the shoulders above the ground, it should be: Shoulder height = L3 + L2 + L1 + PD/2 - HJ + TR. Dimension HJ represents where the hip joint is located above the saddle.
Dimension A2 is from the elbow to the edge of the grip.
If there is ever any confusion about what dimensions mean in BikeCAD, be aware that most dimensions can be shown on the screen using the Dimensions dialog box. It can also be insightful to change the dimension value to some very large number or some very small number and watch how that affects the model.
Thank you Brent. That was helpful. I'll do some measuring on a test subject and will also experiment with changing one dimension at a time to see the effect on the model.