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snapmap - map a snapshot into a 2D image
snapmap in=snapshot
out=image [parameter=value]
snapmap "grids" two arbitrary bodytrans(3NEMO)
expressions (default: x, and y) of a snapshot into a 2D map, using another
bodytrans(3NEMO)
expression (default: -vz) as the map value. The result is
an image(5NEMO)
, with optional astronomical projection for direct comparision
with true astronomical images. There are a number of way implemented to
"grid" the particles: mean value, with or without gaussian weighting, and
forms of linear interpolation.
Use snapgrid(1NEMO)
instead to grid datacubes
(e.g. X-Y-Z), or if you need various styles of line of sight integrations. snapmap
is more appropriate to obtain well interpolated maps from irregularly sampled
data where the input mapping I(x,y) is still a smooth function, although
good results can also be ontained by averaging the values (the default
mode) or using a smoothing length svar=.
Parameters
The following parameters
are recognized:
- in=in-file
- input file, must be in snapshot(5NEMO)
format.
Multiple snapshots can be stacked uses the times= keyword: see stack= below.
[no default].
- out=out-file
- output file, will be in image(5NEMO)
format. Note
that multiple times and/or multiple evar's will produce multiple images
in this file. [no default].
- times=t1:t2,t3,..
- Selection of the times of snapshots
to be selected for gridding. For stack=t all snapshots will be co-added into
one image, however selecting stack=f or selecting multiple evar's one can
request multiple output images. [Default: all].
- xrange=xb:xe
- Range in xvar
to bin. Note these are the outer edges, not their cell centers. [default:
-2:2].
- yrange=xb:xe
- Range in yvar to bin [default: -2:2].
- xvar=x-expression
- The value of x-expression is gridded along the X axis. [default: x].
- yvar=y-expression
- The value of y-expression is gridded along the Y axis. [default: y].
- evar=e1,e2,...
- Variable(s) to denote the emissivity per particle. The default matches
that of snapgrid(1NEMO)
's zvar=. Multiple expressions, separated by commas,
can be given, each of them generating an image. [default: -vz].
- svar=smoothing
- Variable to denote gaussian weighting size in X and Y. Note this is the
gaussian sigma, not the FWHM (FMHW = 2.355 * sigma). Only used if mode=mean.
- nx=x-pixels
- Number of pixels along the X axis of the image [default: 64].
- ny=y-pixels
- Number of pixels along the Y axis of the image [default: 64].
- xlab=x-label
- Text used to label the X-axis. By default the xvar expression
is used. It may be useful in certain astronomical environment to label the
axis with recognized labels like RA---TAN, DEC--SIN, GLON etc.
- ylab=y-label
- Same
for the Y-axis.
- mode=gridding-mode
- mean (can be optionally with gaussian weighting),
linear interpolation [Default: mean].
- stack=t|f
- Should all snapshots from
the input file be stacked, or write one image per selected (see times=)
time? [default: f].
- proj=
- If a valid projection type (SIN, TAN, ARC, NCP,
GLS, MER, AIT) but see also wcs(1NEMO)
, the input coordinates are interpreted
in angular degrees, and griddes with the appropriate sky projection. Default:
no sky projection.
Combinations of large snapshots and large images
may run into memory problems since both the snapshot and the image(s) must
fit into memory to obtain turbo speeds.
Sky projections do not guarantee
flux conservation, interpolation is done in linear space.
This program
was written to create maps with more accurate interpolated velocity fields
from models. However, in the default mode it used the same mean pixel value
as snapgrid(1NEMO)
:
snapmap snap101 ccd101
snapgrid snap101 ccd102 evar=-vz mean=t
ccdmath ccd101,ccd102 - %1-%2 | ccdstat -
Min=0.000000 Max=0.000000
...
produces the same images ccd101 and ccd102 from the input snapshot snap101
snapgrid(1NEMO)
, snapifu(1NEMO)
, snapsmooth(1NEMO)
, snapccd(1NEMO)
,
ccdintpol(1NEMO)
, image(5NEMO)
Peter Teuben
src/nbody/image snapmap.c
20-jun-09 V1.0: created PJT
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