Add to WCS tutorial: How to place a scale bar on an image with WCS #443

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1. eblur

   added

   content-modify

   on Apr 14, 2020
2. kakirastern commented on Apr 14, 2020

   

   kakirastern

   on Apr 14, 2020

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   @eblur Yeah, I agree that it would be a good idea!
3. kakirastern commented on Apr 28, 2020

   

   kakirastern

   on Apr 28, 2020

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   Have used matplotlib's axes.arrow for the plotting of a scale bar on an image in the Celestial Coordinates 1 (or celestial-coords1) notebook on Google Colab, with a wcs transform thrown in so that I can directly enter the degrees for the attributes for plotting. Maybe this simplified version would be more suitable for our purposes.
4. adrn

   closed this as completedin #453on Sep 16, 2020
5. keflavich commented on Jul 6, 2021

   

   keflavich

   on Jul 6, 2021

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   Even though this was closed... I don't see this material in the tutorials. This is the snippet I use. Should we consider adding to core?

   def make_scalebar(ax, left_side, length, color='w', linestyle='-', label='',
                     fontsize=12, text_offset=0.1*u.arcsec):
       axlims = ax.axis()
       lines = ax.plot(u.Quantity([left_side.ra, left_side.ra-length]),
                       u.Quantity([left_side.dec]*2),
                       color=color, linestyle=linestyle, marker=None,
                       transform=ax.get_transform('fk5'),
                      )
       txt = ax.text((left_side.ra-length/2).to(u.deg).value,
                     (left_side.dec+text_offset).to(u.deg).value,
                     label,
                     verticalalignment='bottom',
                     horizontalalignment='center',
                     transform=ax.get_transform('fk5'),
                     color=color,
                     fontsize=fontsize,
                    )
       ax.axis(axlims)
       return lines,txt
6. kelle commented on Jul 8, 2021

   

   kelle

   on Jul 8, 2021

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   There is an implementation of a scale bar in Section 3 of Working with Celestial Coords with WCS I. So, as far as I'm concerned, from a Tutorial perspective, this is addressed.

   If you want to propose to add it to core -- which makes total sense -- I assume you'd want to open that issue/PR in a different repo.

   fig = plt.figure(figsize=(10, 10), frameon=False)
   ax = plt.subplot(projection=wcs_helix)
   ax.arrow(337, -21.2, 0, 0.1,
            head_width=0, head_length=0,
            fc='white', ec='white', width=0.003,
            transform=ax.get_transform('icrs'))
   plt.text(337.05, -21.18, '0.1 deg',
            color='white', rotation=90,
            transform=ax.get_transform('icrs'))
   plt.imshow(image, origin='lower', cmap='cividis', aspect='equal')
   plt.xlabel(r'RA')
   plt.ylabel(r'Dec')

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