bike frame size calculation program

[Emanuel Berg]

I just made an update to my bike frame size
calculation program, now it does inches, and
road bikes, as well as cm and MTBs.
Comments/corrections/etc welcome...

;;; -*- lexical-binding: t -*-

;; This file: http://user.it.uu.se/~embe8573/emacs-init/frame-size.el
;;            https://dataswamp.org/~incal/emacs-init/frame-size.el
;;
;; Update history:  2019-05-06  02:51  first release
;;                  2019-07-31  06:33  - got away w/ globals
;;                                     - support for road bikes
;;                                     - size in inches as well as cm
;;
;; frame size = length of seat tube
;;
;; measured from the top of the seat tube
;; down to the center of the bottom bracket
;; 
<https://www.ebicycles.com/bicycle-tools/measure-frame/mountain-bike/hardtail>
;;
;;
;;   rider height           MTB frame size
;;
;;            (cm)                       (cm)
;;
;; 4'10" -    148 -     13" - 14"       33 - 37
;; 5'2"       158
;;
;; 5'2"  -    158 -     15" - 16"       38 - 42
;; 5'6"       168
;;
;; 5'6"  -    168 -     17" - 18"       43 - 47
;; 5'10"      178
;;
;; 5'10" -    178 -     19" - 20"       48 - 52
;; 6'1"       185
;;
;; 6'1"  -    185 -     21" - 22"       53 - 57
;; 6'4"       193
;;
;; 6'4"  -    193 -     23" - 24"       58 - 61
;; 6'6"       198
;; <https://www.evanscycles.com/help/bike-sizing-mountain>
;;
;;
;; Example how to do the interval math for
;; a particular height
;;
;;     height h = 190 cm
;;
;;     h \in [185 193] cm so
;;
;;     MTB frame size m \in [53 57] cm
;;
;;     (190 - 185)/(193 - 185.0) * (57 - 53) + 53 cm = 55.5 cm
;;
;;
;; note: border cases will favor the smaller
;;       frame, because experience tells us
;;       this makes sense

(defun in-inclusive (a min max)
  (and (<= min a)
       (<= a max) ))

(defun compute-frame-size (h mtb)
  (let*((table (if mtb '(((148 158) (33 37)) ; height to frame size
                         ((158 168) (38 42))
                         ((168 178) (43 47))
                         ((178 185) (48 52))
                         ((185 193) (53 57))
                         ((193 198) (58 61)) )
                 '(((168 175) (54 55)) ; ditto road bike (URL source?)
                   ((175 183) (56 58))
                   ((183 191) (58 60)) )))
        (intervals (cl-find-if (lambda (e)
                                 (in-inclusive h     (caar e)
                                                 (cl-cadar e) ))
                               table) )
        (h-interval  (car  intervals))
        (m-interval  (cadr intervals))
        (h-min (caar intervals))
        (h-max (cadr h-interval))
        (m-min (car  m-interval))
        (m-max (cadr m-interval))
        (frame-cm (+ (* (/ (- h     h-min)
                           (- h-max h-min)
                           1.0)
                        (- m-max m-min) )
                     m-min) )
        (frame-cm-round (round frame-cm))
        (frame-inches (round (/ frame-cm 2.54))) )
    (message "frame size: %d cm (%d inches)"
             frame-cm-round frame-inches) ))

;; MTB test:
;; (compute-frame-size 180 t) ; "frame size: 49 cm (19 inches)"
;; (compute-frame-size 190 t) ; "frame size: 56 cm (22 inches)"

;; RB test:
;; (compute-frame-size 180 nil) ; "frame size: 57 cm (23 inches)"
;; (compute-frame-size 190 nil) ; "frame size: 60 cm (24 inches)"

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal