Hi there, You will need to normalise (0 - 1) your data set first. To interpolate, you will need to pass normalised values, as well. Then you can unscale the output in the range you want. On Mon, Sep 30, 2019 at 1:51 AM hgrwilson via Boost-users < boost-users@lists.boost.org> wrote:

Hi all,

I am trying to interpolate some data with a *catmull_rom* spline available in boost math (interpolation). However, the resulting spline collapses to a single point for all /s/, corresponding to the first control point, /points_intr[0]/.

Below, the c++ code segment of the interpolation is depicted:

std::vector> points_intr(16);

points_intr[0] = { 1.263270, 0.774614 }; points_intr[1] = { 1.876, 2.480 }; points_intr[2] = { 1.651110, 4.550 }; points_intr[3] = { 1.426340, 5.688 }; points_intr[4] = { 1.429, 7.054 }; points_intr[5] = { 2.073220, 8.377020 }; points_intr[6] = { 3.910, 9.140 }; points_intr[7] = { 6.430, 9.537 }; points_intr[8] = { 8.950, 9.859 }; points_intr[9] = { 11.470, 10.317 }; points_intr[10] = { 12.730, 10.6456 }; points_intr[11] = { 13.990, 11.0741 }; points_intr[12] = { 15.335, 11.6928 }; points_intr[13] = { 16.680, 12.5661 }; points_intr[14] = { 18.3538, 14.830 }; points_intr[15] = { 18.700, 16.056 };

boost::math::catmull_rom> interpolator_cr(std::move(points_intr));

auto max_s = interpolator_cr.max_parameter(); std::array inter_points; for (int i = 0; i < 100; i++) { inter_points = interpolator_cr(max_s * (i / num_points)); geometry_msgs::Point p; p.x = inter_points[0]; p.y = inter_points[1]; p.z = z; //p.z = inter_points[2]; marker.points.push_back(p); DEBUG_INFO("spline %d: (x, y) %f, %f, current_s: %f", i, p.x, p.y, max_s * (i / 100.0)); }

I'm using boost 1.71.0

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The problem is in this line: inter_points = interpolator_cr(max_s * (i / num_points)); i/num_points rounds to zero. I just reproduced your code with the fix: #include <iostream> #include #include <vector> #include <array> int main() { std::vector> points_intr(16); points_intr[0] = { 1.263270, 0.774614 }; points_intr[1] = { 1.876, 2.480 }; points_intr[2] = { 1.651110, 4.550 }; points_intr[3] = { 1.426340, 5.688 }; points_intr[4] = { 1.429, 7.054 }; points_intr[5] = { 2.073220, 8.377020 }; points_intr[6] = { 3.910, 9.140 }; points_intr[7] = { 6.430, 9.537 }; points_intr[8] = { 8.950, 9.859 }; points_intr[9] = { 11.470, 10.317 }; points_intr[10] = { 12.730, 10.6456 }; points_intr[11] = { 13.990, 11.0741 }; points_intr[12] = { 15.335, 11.6928 }; points_intr[13] = { 16.680, 12.5661 }; points_intr[14] = { 18.3538, 14.830 }; points_intr[15] = { 18.700, 16.056 }; boost::math::catmull_rom> interpolator_cr(std::move(points_intr)); auto max_s = interpolator_cr.max_parameter(); std::array inter_points; for (int i = 0; i < 100; i++) { double arg = max_s*i/double(100); inter_points = interpolator_cr(arg); std::cout << "p(" << arg << ") = (" << inter_points[0] << ", " << inter_points[1] << ")\n"; } } No need to normalize your data. Nick ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Sunday, September 29, 2019 8:46 PM, hgrwilson via Boost-users wrote:

Hi all,

I am trying to interpolate some data with a catmull_rom spline available in boost math (interpolation). However, the resulting spline collapses to a single point for all /s/, corresponding to the first control point, /points_intr[0]/.

Below, the c++ code segment of the interpolation is depicted:

std::vector> points_intr(16);

points_intr[0] = { 1.263270, 0.774614 }; points_intr[1] = { 1.876, 2.480 }; points_intr[2] = { 1.651110, 4.550 }; points_intr[3] = { 1.426340, 5.688 }; points_intr[4] = { 1.429, 7.054 }; points_intr[5] = { 2.073220, 8.377020 }; points_intr[6] = { 3.910, 9.140 }; points_intr[7] = { 6.430, 9.537 }; points_intr[8] = { 8.950, 9.859 }; points_intr[9] = { 11.470, 10.317 }; points_intr[10] = { 12.730, 10.6456 }; points_intr[11] = { 13.990, 11.0741 }; points_intr[12] = { 15.335, 11.6928 }; points_intr[13] = { 16.680, 12.5661 }; points_intr[14] = { 18.3538, 14.830 }; points_intr[15] = { 18.700, 16.056 };

boost::math::catmull_rom> interpolator_cr(std::move(points_intr));

auto max_s = interpolator_cr.max_parameter(); std::array inter_points;

for (int i = 0; i < 100; i++) { inter_points = interpolator_cr(max_s * (i / num_points)); geometry_msgs::Point p; p.x = inter_points[0]; p.y = inter_points[1]; p.z = z; //p.z = inter_points[2]; marker.points.push_back(p); DEBUG_INFO("spline %d: (x, y) %f, %f, current_s: %f", i, p.x, p.y, max_s * (i / 100.0)); }

I'm using boost 1.71.0

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