Once-Asked Questions

Q: I don’t have numpy. What do I do?

“import error: no module named numpy”

A: Disable things that require numpy.

Some parts of the code need the “numpy” python package. To disable things that need numpy:

solve-field --no-remove-lines --uniformize 0  [....usual arguments...]

Q: Is there a way to plot a grid of RA and Dec on the images?

A: Yes

You’ll have to run the “plot-constellations” program separately. For example, if you have an image 1.jpg and WCS 1.wcs:

jpegtopnm 1.jpg | plot-constellations -w 1.wcs -o grid.png -i - -N -C -G 60

will plot an RA,Dec grid with 60-arcminute spacings. Unfortunately they’re not labelled…

[Note, see plotann.py also for more annotation options.]

Q: Is there a way to get out the center of the image (RA,Dec) and pixel scale of the image?

A: Yes, with the wcsinfo program

Yes, run the “wcsinfo” program on a WCS file – it prints out a bunch of stats, in a form that’s meant to be easy to parse by programs (so it’s not particularly friendly for people). “ra_center” and “dec_center” (in degrees) and “pixscale” (in arcsec/pixel) are what you want.

Q: Is there a way to plot N and E vectors on the image?

A: Not yet.

Q: Is there a way to plot a list of your own objects on the image by inputing RA,Dec?

A: Check out plotann.py, or try these older instructions…

Yes – but it’s roundabout…

First, project your RA,Dec objects into pixel x,y positions:

wcs-rd2xy -w 1.wcs -i your-objs.rd -o your-objs.xy

Then plot them over the image (or annotated image). There’s not currently a way to label them.


pngtopnm grid.png | plotxy -i your-objs.xy -I - -x 1 -y 1 -s X -C green -b black > objs.png

The “-x 1 -y 1” compensate for the fact that FITS calls the center of the first pixel (1,1) rather than (0,0).

Q: Would your code work on all-sky images?

A: Not very well

We assume a TAN projection, so all-sky images typically don’t work, but it should certainly be possible with a bit of tweaking, since all-sky is really a much easier recognition problem! One thing you can try, if your image is big enough, is to cut out a small section near the middle.

Q: I want to build an index from my own catalog. How do I proceed?

A: See Index