The previous fs2d-scl.diderot program makes a little dataset
in which we can try to find isosurfaces:
../fs2d/fs2d-scl -size0 50 -size1 50 -which tcubic -width 8 | unu save -f nrrd -o cubic.nrrd
rm out.nrrd
Then compile this program:
diderotc --exec iso2d.diderot
and try ./iso2d --help to see the available input variables. See
the info with vimg.diderot about how Diderot handles input arrays.
To run isocontour sampling (starting with a 100x100 grid of points), at the default isovalue 0:
./iso2d -cmin -4 -4 -cmax 4 4 -size 100
This saves the output positions into pos.nrrd as a list of 2-vectors, which
can be seen by running unu head pos.nrrd. You can convert this to a
text file with unu save -f text -i pos.nrrd -o pos.txt.
In any case, Diderot doesn't itself supply a way of visualizing this point set; some other graphics or plotting program is needed. A really quick-and-dirty way of showing the points is as a joint histogram of their X and Y coordinates:
unu jhisto -i pos.nrrd -b 500 500 -min -4 4 -max 4 -4 -t float |
unu 2op gt - 0 |
unu quantize -b 8 -o pos.png
Make sure your pos.png looks like pos-ref.png; it may
not be an exact pixel match but it should be close. If pos.png
looks very different (or blank), your Teem checkout may be old (a new
fix was committed Nov 5 2015). Assuming your PNG viewer uses
conventional display orientation, the -min -4 4 -max 4 -4 arguments
to unu jhisto should make the first coordinate ("x") increase to the
right, and the second coordinate ("y") increase towards up.
As noted with the vimg.diderot example, even if you compiled
with one proxy file, you can
supply a different file at run-time, as long as the new file matches
the type and shape of the proxy image. We can add some noise
to the dataset, and then add a little ramp along the Y axis (to explicitly
break the over-all symmetry of the isocontour):
unu 2op nrand cubic.nrrd 0.5 -s 42 -o noisy.nrrd
../fs2d/fs2d-scl -size0 50 -size1 50 -which y -width 8 | unu save -f nrrd -o yramp.nrrd
rm out.nrrd
unu 2op x yramp.nrrd 3 | unu 2op + noisy.nrrd - -o noisy.nrrd
and then re-run the isocontouring and display on the new data.
./iso2d -cmin -4 -4 -cmax 4 4 -size 100 -img noisy.nrrd -o pos2.nrrd
unu jhisto -i pos2.nrrd -b 500 500 -min -4 4 -max 4 -4 -t float |
unu 2op gt - 0 |
unu quantize -b 8 -o pos2.png
Make sure your pos2.png looks like pos2-ref.png.
Things to try (to see their effect on the output positions, both the number of outputs and their location):
- increasing or decreasing
stepsMax - increasing or decreasing
epsilon - increasing or decreasing
size; if it goes too low then the program will not have any output