+# frame is integer 9 bits, result is laserdiff time in us
+def frame_to_us(frame):
+ d = frame_to_mm(frame)
+ a = 2 * math.asin(LASER_RADIUS/d)
+ t = (a * (1000000./RPS)) / (2. * math.pi)
+ return t
+
+# theorical: laser timediff to robot distance
+def us_to_mm(us):
+ return frame_to_mm(us_to_frame(us))
+
+# theorical: robot distance to laserdiff
+def mm_to_us(mm):
+ return frame_to_us(mm_to_frame(mm))
+
+def time_us_to_tick(us):
+ return (us / 1000000.) * TIMER_FREQ
+
+def time_tick_to_us(t):
+ return (t * 1000000.) / TIMER_FREQ
+
+
+##################
+
+# linear correction: distance_mm, time_us
+# must be ordered
+samples = [
+ (250., 2201.),
+ (450., 701.),
+ (1200., 231.),
+ (3000., 50.),
+ ]
+
+dist_mm = map(frame_to_mm, range(512))
+
+# theorical curve
+theorical = [0] * 512
+for i in range(512):
+ theorical[i] = frame_to_us(i)
+
+# find offset and update theorical curve
+off = samples[-1][1] - mm_to_us(3000.)
+print "offset=%f"%(off)
+theo_off = [0] * 512
+for i in range(512):
+ mm = frame_to_mm(i)
+ theo_off[i] = mm_to_us(mm) + off
+
+final = [0] * 512
+for i in range(512):
+ mm = frame_to_mm(i)
+
+ # find between which samples we are
+ smp = 0
+ while smp < (len(samples) - 2):
+ if samples[smp+1][0] >= mm:
+ break
+ smp += 1
+
+ mm_start = us_to_mm(samples[smp][1] - off)
+ mm_end = us_to_mm(samples[smp+1][1] - off)
+
+ # interpolation
+ ratio = (mm - samples[smp][0]) / (samples[smp+1][0] - samples[smp][0])
+ mm_new = mm_start + ratio * (mm_end - mm_start)
+
+ final[i] = mm_to_us(mm_new) + off
+
+sample_idx = 0
+while sample_idx < len(samples):
+ print samples[sample_idx][1],
+ print us_to_mm(samples[sample_idx][1] - off),
+ print mm_to_us(samples[sample_idx][0])
+ sample_idx += 1
+
+
+plt.plot(
+# dist_mm, theorical, "r-",
+# dist_mm, theo_off, "b-",
+ dist_mm, final, "g-",
+ map(lambda x:x[0], samples), map(lambda x:x[1], samples), "g^",
+ )
+plt.show()
+