interpolation – Make Me Engineer

interpolate 3D volume with numpy and or scipy

June 13, 2023 by Tarik

In scipy 0.14 or later, there is a new function scipy.interpolate.RegularGridInterpolator which closely resembles interp3. The MATLAB command Vi = interp3(x,y,z,V,xi,yi,zi) would translate to something like: from numpy import array from scipy.interpolate import RegularGridInterpolator as rgi my_interpolating_function = rgi((x,y,z), V) Vi = my_interpolating_function(array([xi,yi,zi]).T) Here is a full example demonstrating both; it will help you understand … Read more

Property binding vs attribute interpolation

June 13, 2023 by Tarik

Property binding like [trueValue]=”…” evaluates the expression “…” and assigns the value “true” evaluates to the value true “Y” is unknown. There is no internal Y value in TypeScript and no property in the component class instance, which is the scope of template binding. In this case you would want [trueValue]=”‘Y'” Note the additional quotes … Read more

Floating point linear interpolation

June 11, 2023 by Tarik

As Jason C points out in the comments, the version you posted is most likely the best choice, due to its superior precision near the edge cases: float lerp(float a, float b, float f) { return a * (1.0 – f) + (b * f); } If we disregard from precision for a while, we … Read more

Reverse complex 2D lookup table

June 4, 2023 by Tarik

for f(x,y) you can use f(x,y)->(a,b) 2D LUT (Look Up Table) But the stored grid points must be selected so dense so that there is max one bump per grid rectangle, otherwise interpolation would not work correctly. If you want to use linear interpolation then the local min/max must be points inside LUT, for polynomial … Read more

problematic Moire pattern in image produced with gnuplot pm3d and pdf output

June 4, 2023 by Tarik

This is not supposed to be a solution, but rather an explanation and a possible, although ugly workaround. From time to time there are reports to the gnuplot mailinglists about this issue, but it seems to be related to the viewers. It has to do with the way gnuplot creates the surfaces plots. These are … Read more

Color Interpolation Between 3 Colors in .NET

June 2, 2023 by Tarik

First, you ask for linear interpolation but you don’t specify that color B lives on the line between color A and color C; this is necessary. Second, you didn’t specify but I am going to make a simplifying assumption that color B is the midpoint of the line between color A and color C; the … Read more

How do I implement a Bézier curve in C++?

May 29, 2023 by Tarik

Recently I ran across the same question and wanted to implemented it on my own. This image from Wikipedia helped me: The following code is written in C++ and shows how to compute a quadratic bezier. int getPt( int n1 , int n2 , float perc ) { int diff = n2 – n1; return … Read more

get x-value given y-value: general root finding for linear / non-linear interpolation function

May 18, 2023 by Tarik

How Do I Generate a 3-D Surface From Isolines?

May 17, 2023 by Tarik

In MATLAB you can use either the function griddata or the TriScatteredInterp class (Note: as of R2013a scatteredInterpolant is the recommended alternative). Both of these allow you to fit a surface of regularly-spaced data to a set of nonuniformly-spaced points (although it appears griddata is no longer recommended in newer MATLAB versions). Here’s how you … Read more

Multivariate spline interpolation in python/scipy?

April 28, 2023 by Tarik

If I’m understanding your question correctly, your input “observation” data is regularly gridded? If so, scipy.ndimage.map_coordinates does exactly what you want. It’s a bit hard to understand at first pass, but essentially, you just feed it a sequence of coordinates that you want to interpolate the values of the grid at in pixel/voxel/n-dimensional-index coordinates. As … Read more