This example shows how it is possible, though not exactly convenient, to do 1D data plotting in Diderot. While such plotting done is normally done with a vector (not a raster) graphics display, this program is still useful to:
- demonstrate the various "border controls" for reconstructing at the edges of index space
- show exactly what the available reconstruction kernels look like
- demonstrate how functions can be "lifted" to fields
The program as distributed here plots the reconstruction of data with the
"ctmr" Catmull-Rom reconstruction kernel, with "clamp" border-control. We can plot
ctmr itself, as the response to an impulse in the data:
echo "0 0 1 0 0" | unu axdelete -a -1 | unu dnorm -rc -o data.nrrd
./plot1d -img data.nrrd -ymm -0.3 1.3
unu quantize -b 8 -i rgb.nrrd -o ctmr.png
To learn more, try changing the program in all the places noted with "Choose ONE by uncommenting", then recompiling, running, and looking at the results.
To plot a function created within Diderot,
uncomment and edit the "or write your own function of F0" line below. If
playing with taking derivates, choose reconstruction with c4hexic for a high
(C^4) continuity order. Be sure to recompile. The following makes data.nrrd
into a linear ramp from (-M,-M) to (M,M), with 4 samples of extra padding to account
for reconstruction kernel support.
M=12;
MP=$((M+4));
echo "-$MP $MP" | unu axdelete -a -1 |
unu resample -s $((2*MP+1)) -k tent -c node |
unu axinfo -a 0 -mm -$MP $MP | unu dnorm -o data.nrrd
./plot1d -img data.nrrd -xmm -$M $M -ymm -4 4
unu quantize -b 8 -i rgb.nrrd -o func.png
Computing the plot as a raster image, with the thickness of plot elements defined in index space, requires conversions back and forth between world and index space, which are currently somewhat cumbersome in Diderot. Using homogeneous coordinate transforms might simplify this (available with matrix-vector multiplications in Diderot), though that would be a very different program.