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1d convolution in c for lidar data smoothing
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| #include <stdio.h> | |
| /* Useful vidoes: | |
| 1d kernel for data processing: | |
| https://www.youtube.com/watch?v=D0F-NPerCIE | |
| numberphile on image bluring (same thing in 2d): | |
| https://www.youtube.com/watch?v=C_zFhWdM4ic | |
| excellent explanations in there. It introduced me to the concept. | |
| */ | |
| // 9 wide 1d kernel, no padding so it cuts out early | |
| // shift by 4 to align with original data | |
| int main(){ | |
| // gassian kernel from: http://dev.theomader.com/gaussian-kernel-calculator/ | |
| float kernel[9] = {0.000229, 0.005977, 0.060598, 0.241732, 0.382928, 0.241732, 0.060598, 0.005977, 0.000229}; | |
| // random number from python, irl this would come from lidar | |
| float data[100] = {7.230, 16.98, 17.99, 1.703, 16.44, 4.484, 7.843, 13.44, 7.815, 11.91, 2.050, 6.138, 3.049, 0.167, 1.756, 10.46, 10.02, 10.48, 13.14, 7.329, 14.93, 7.275, 18.61, 13.82, 15.97, 11.43, 10.27, 5.290, 14.13, 2.671, 3.267, 6.149, 14.56, 13.11, 18.14, 16.47, 17.49, 16.20, 7.835, 5.883, 0.967, 0.237, 4.359, 13.15, 15.92, 16.94, 14.30, 17.47, 5.118, 5.142, 19.41, 5.046, 16.78, 3.944, 12.17, 7.983, 15.35, 7.839, 11.65, 12.56, 9.564, 14.30, 4.670, 1.893, 9.304, 0.173, 3.921, 15.63, 6.561, 16.25, 1.634, 4.870, 15.03, 0.269, 11.92, 0.390, 15.57, 2.918, 8.966, 14.04, 11.23, 7.519, 7.943, 6.570, 18.74, 15.54, 1.303, 14.01, 1.797, 1.526, 12.90, 3.051, 8.602, 7.094, 14.39, 14.13, 11.20, 2.637, 2.644, 2.810}; | |
| // empty array to store the output | |
| float output[100-9]; | |
| // keep track of max and max_index | |
| float max = 0; | |
| int max_index; | |
| printf("\nshow data and output as it is calculated:\n"); | |
| //loop over data | |
| for (int i = 0; i < 100-9+1; i++){ | |
| // don't trust that c will zero the array for us | |
| output[i] = 0; | |
| //loop over kernel for each datapoint | |
| for (int j = 0; j < 9; j++){ | |
| output[i] += kernel[j] * data[i+j]; | |
| } | |
| // check if it wins against max, then set max_index | |
| if (output[i] > max){ | |
| max = output[i]; | |
| max_index = i; | |
| } | |
| // print data then blurred output as it is calculated | |
| printf("%d: %f\t%f\n", i, data[i], output[i]); | |
| } | |
| printf("\nShifted over to show true location:\n"); | |
| // iterate over data again and show where value is centered on | |
| for (int i = 0; i < 100; i++){ | |
| // print data then blurred output shifted | |
| if (i >= 4 && i < 100-4){ | |
| printf("%d: %f\t%f\n", i, data[i], output[i-4]); | |
| } else{ | |
| printf("%d: %f\t\n", i, data[i]); | |
| } | |
| } | |
| printf("Max value: %f, location of max value: %d\n", max, max_index+4); | |
| } | |
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