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5.2.4 Integrated Color Maps

A true color map can be created from a snapshot by assigning a color to the particles in the snapshot. This can be done by gridding the snapshots twice, each one assigning the particles with a different emissivity. In the example below a snapshot is assigned an artificial radial color gradient. The particles are given a linearly increasing emissivity, according to their ranking in radius. First, we must make sure the snapshot is sorted in radius properly:

    30% snapsort in=snap.dat out=tmp1 rank=r

and next the snapshot is gridded twice:

    31% snapgrid in=tmp1 out=tmp1_1 evar=m
    32% snapgrid in=tmp1 out=tmp1_2 evar='m*(i+1)'

This means the color at the center would be $-2.5log(I_1/I_2) = 0$, whereas at the edge the color would be $2.5log(nbody)$. The images are best viewed when smoothed, and then divided and taken the log of. The factor 2.5 is left out here, because the scaling is arbitrary:

    33% ccdsmooth in=tmp1_1 out=tmp1_1s gauss=0.3
    34% ccdsmooth in=tmp1_2 out=tmp1_2s gauss=0.3
    35% ccdmath in=tmp1_1s,tmp1_2s out=color_ccd.dat fie='log(%2/%1)'

........... more to come

(c) Peter Teuben