Beaglebone Black and Astrophotography: Phase 2: iAstroHub tweaks

While I was able to setup nearly all of the software for iAstroHub on my Beaglebone Black (still some issues with gphoto), the interface just wasn't working quite right.  So, I enlisted my PHP guru brother to help.

Nginx setup
Edit /etc/php5/fpm/php.ini and turn short_open_tag On in order for things to be happier.

@awnage: The javascript on the main page calls several other pages to display data. This is usually termed AJAX. Those calls were being made to php scripts that used <? (shorttags) instead of <?php. <? is an old PHPv3 standard that has been out of favor for quite some time. Changing the ini setting allows those files to run properly. There is no security concern with this.

Software locations and additional setup
Your lin_guider package is expected to be in the /home/pi directory.  So, the executable path should look like:
/home/pi/lin_guider_pack/lin_guider/lin_guider

When lin_guider is run, it will be done as root.  Consequently, the setup of lin_guider needs to be done as root so that appropriate configuration files are placed in the root's home directory.  If you are logging in in remotely via ssh -X, you will probably have to copy the .Xauthority file from your user account to the root home directory in order to export the lin_guider GUI.  Or, once you have the web interface running, you can use VNC to connect and see the lin_guider interface for setup.

Permissions
Make sure all the text files in /home/pi/www are editable by pi:www-data.

# chown -R pi:www-data /home/pi/www
# chmod 644 /home/pi/www*.txt

Make sure the executables in /home/pi/www/guidestar can be executed by pi.

# chmod ug+x /home/pi/www/guidestar/cmd_getimage
# chmod ug+x /home/pi/www/guidestar/cmd_setposition

SkySafari and iOS Browsers
So, iAstroHub has the cool feature of being able to plate-solve (i.e. figure out where in the sky an image was taken) and then load the solution in SkySafari Plus/Pro.  Anat has a video of the process.  Unfortunately, most browsers on iOS don't allow for downloading of files.  You can of course look at the raw text of the file when clicking on the "Get result for SkySafari" link.  The Mercury browser does allow downloading, but it strips the file extension, and you cannot open it in SkySafari.

After a bit of searching, the Atomic browser is what Anat is using.  You will need the full version, which is a bargain at $1.99 currently.  Unfortunately, the download functionality doesn't work in iOS 7.  Fortunately, my wife's iPad is still on iOS 6.

I see that the iCab browser allows for downloading of files.  Using the same procedure (click and hold on link->save->open in external app) you can get the SkySafari file into your SkySafari app.  $1.99 also.  Wonder if I can get my $1.99 back for Atomic....

It is probably worthwhile to have a VPN Client in case something goes funky with lin_guider.  I also have the pTerm app so that I can login to the BBB from iOS.

Beaglebone Black and Astrophotography: Phase 2: Building astronomy software

Install astronomy software.
So, this is going to be based on the work by Anat Ruangrassamee, written up at www.cloudynights.com, and his iAstroHub project.  His project files can be obtained here: http://sourceforge.net/projects/iastrohub/

Open the README.txt and follow the "HARD WAY".  Some of the stuff we have already done.
Step 1-2: Skip.  Steps 3-4: I am not sure it is entirely necessary to give open access in sudo, but for now we will follow the instructions.  Steps 5-6: BTDT.  Step 7: Sure.  I use vi instead of nano, so I left that out.

Step 8: We need to shutdown apache in favor of nginx.

# update-rc.d -f  apache2 disable

# apachectl stop

Then continue to follow the iAstroHub instructions.
Make sure that you can still connect to your access point and webpage.  Mine is still at 192.168.4.1, and I now see that is running nginx as opposed to Apache.

Step 9:  I followed the instructions, and got a failure.  Instead (you will want unzip for later):

# apt-get install gphoto2 unzip

That being said/written, it does not look like the gphoto2-6 package works later in step 20, so I will revisit compilation later.

Step 10: It is not mentioned, but grab the latest lin_guider from linguider.sourceforge.net.  The "copy modified files" means to copy the files from the Modified codes/linguider folder in the iAstroHub package to the lin_guider_pack/lin_guider/src directory of lin_guider.

The setup of lin_guider is through a GUI.  So, you either need to have a monitor hooked up to the BBB, or you need to be exporting the graphics via ssh -X.  Woohoo!  I can see from my webcam after the device setup.

Step 11: The mentioned package is available from http://en.sourceforge.jp/projects/sfnet_cccd/releases.  I am uncertain if it does any good for webcams.

Step 12-13: Sure.  This is starting to take up a fair bit of space....  

Step 14: The pip install pyephem step should probably be sudo pip install pyephem. When setting up astrometry, the modified starutil.c goes in util, and solve-field.c goes in the blind directory.

The make on astrometry fails for me with:

collect2: error: ld returned 1 exit statusmake[1]: *** [libbackend.so] Error 1make[1]: Leaving directory `/home/ubuntu/projects/astrometry.net-0.40/blind'make: *** [subdirs] Error 2

So, according to the astrometry google group, you can get around this by doing: sudo make -k since libbackend.so apparently isn't needed for astrometry.  At this point I needed to do a sudo apt-get clean so that I had enough space on my BBB to continue.  Actually, at this point I realized that there will not be enough space on the BBB's eMMC memory for all of this, which means expanding to 8+ GB and booting off the microSD (and editing my first post).

You need to get plate solving index files from http://data.astrometry.net/4200/.  Read the http://www.astrometry.net/doc/readme.html to figure out what indexes you need.  Anat has some recommendations, post 6193995.  Since my scope is a WO GTF81 using prime focus, I will try indices 4208-4210.fits.  Just copy them to the /usr/local/astrometry/data folder.

Step 15: Already configured our Wifi.

Step 16:  I have a Sabrent SBT-USC1M USB to Serial cable using a Prolific PL2303 chip (according to Amazon), so I am more interested in the pl2303.ko module.  Fortunately, this build of Ubuntu already has the modules.  Bonus!  Thanks to Anat for pointing this out to me and suggesting I do serial via UART and save a USB port (Phase 3/4).

Step 17: This configuration might change if a do a UART to serial.  Copying for now.  Port is 3300.

Step 18: We already setup our access point (previous post).  The MK80 apparently uses eth0 for it wireless, while we use wlan0.  I am keeping my dhcp range in 192.164.4.x, but it is probably a good idea to change the lease time to 8 or 12 hours in /etc/dnsmasq.conf and restart the service.

Step 19: This section is for starting up services on boot and creating a virtual X server.

Step 20: ccd_1.2.7.tar.bz2 is obtained from http://sourceforge.net/projects/cccd/files/ccd/1.2.7/.  This is for controlling your imaging CCD or DSLR.  I don't have one (yet, since I am using a micro four thirds camera) but I will build it anyhow.  My Ubuntu distribution has gphoto2-6 and fails to compile.  It looks like there is a known bug.  I will come back to this.  Guess I will have to build gphoto, per step 9.

Step 21: Sure.  

Step 22: lazarus 1.0.10 is in the repository, so I apt-get'd it instead of building, although it added an additional 698 MB worth of packages.  Unfortunately, this doesn't work, as a Raspberry Pi user found out.  So, lets build from source.

# svn checkout http://svn.freepascal.org/svn/lazarus/tags/lazarus_1_0_12

# cd lazarus_1_0_12

# make clean; make

# chmod 777 /home/pi/lazarus_1_0_12 -R

Continue to configure lazarus as appropriate.  With lazarus and fpc installed, the skychart configure line looks like:

# ./configure fpc=/usr/lib/fpc/2.6.2 lazarus=/home/pi/lazarus_1_0_12 prefix=/usr/local

Some directories are missing in skychart which prevents it from compiling.  While in skychart-3.8-2450-src:

# mkdir skychart/component/lib/arm-linux-gtk2

# mkdir skychart/units/arm-linux-gtk2

# mkdir varobs/units/arm-linux-gtk2

Then proceed with building and installing.  During configuration of "Telescope type", there was not a direct option for my mount (Celstron Advanced VX) so I chose Celestron GPS.  Fingers crossed.

Step 23-25: Don't really apply.  No audio DSP in the BBB from what I understand.

Reboot.  Grabbed my (wife's) iPad, installed SkySafari Plus, and pointed my WiFi at the BBB.  Go to settings in SkySafari Plus (or Pro if you have that).  Choose your mount (Celestron NexStar/Advanced GT works for my VX).   Use the appropriate network settings.  Mine is still 192.168.4.1, but Anat's instructions have the network on 10.0.0.1 IIRC.  We previously (step 17) set the serial port to communicate on port 3300.  Connect to the telescope, and presto!  I can control the scope!  Of course, if I just wanted SkySafari control, all I really needed to do was get the access point setup and install/configure ser2net (Step 17).

Phase 3: GPIO-based guide port interface
for the next post...

Beaglebone Black and Astrophotography: Phase 1: Configuring the BBB

Goals for Phase 1
Boot Linux on BBB.
Activate WiFi access.
Activate webcam.

Parts list for Phase 1
Beaglebone Black (BBB)
4-Port powered USB hub
USB WiFi adapter with Access Point capability
5V 2A PSU
Ethernet cable
USB webcam
HDMI to mini-HDMI cable (optional)
8GB+ microSD card

I purchased my Beaglebone Black version A3, PSU, and USB WiFi adapter from Adafruit, and they were quickly delivered.  The BBB comes with a USB to mini USB cable.  The USB hub, webcam (a Logitech C300), and microSD (32GB UHS-I Class 10) were ordered via Amazon.com.  I had an ethernet cable sitting around.

Useful online tutorials
The following are some resources that I found useful for setting up my BBB.
http://learn.adafruit.com/beaglebone
http://derekmolloy.ie/category/embedded-systems/beaglebone/
Plus others

Boot Linux on BBB
Technically, you can just power-up the BBB, and Linux will boot.  However, after a bit of playing, I found out that the Angstrom Linux distribution that was preinstalled on my BBB's eMMC memory was from 2012.  So, I wanted to get updated...
[edit 2013/12/12: due to size limitations of the eMMC memory, you will need to boot off the microSD and install your software there.  Follow these instructions for resizing your microSD boot partition]

I started by using Debian linux (3.2.51-1) via Virtualbox on a Windows 8 PC in order to control and program on my BBB.  You can look elsewhere for how to setup Virtualbox and install a version of Linux.  I was originally thinking of using a Raspberry Pi, and Raspbian is a derivative of Debain, hence the Linux "flavor" choice.  Ubuntu seems to be popular for BBB users, so the choice in *nix/*nux is up to you.  I switched to Ubuntu to make my life easier, but found it had connectivity problems with the usb-to-ethernet system, so I went back to Debian until I got ethernet running.

I suggest you follow some of the online tutorials for getting started, since there are plenty out there.  When you first connect your BBB to your computer via the USB cable, it will appear as a mass storage device.  There are Windows and OS X drivers on it.  I noticed that the Windows drivers are unsigned, so they will not load in Windows 8 without some tricks.  I didn't bother with that.  Instead I passed the BBB through to my Linux virtual machine (VM) in Virtualbox.  Then do the initial setup as suggested at beagle board.org/static/beaglebone/latest/README.htm

Another good site:
http://derekmolloy.ie/beaglebone/getting-started-usb-network-adapter-on-the-beaglebone/
BBB Angstrom flasher 2013.09.12.  http://downloads.angstrom-distribution.org/demo/beaglebone/

I fought with the Angstrom distribution for a while (and had a long blog post written) before I got frustrated enough with connmand and wifi network configuration to scrap it.  Install Ubuntu on your BBB instead and save some headaches.  You can probably save some headaches by not getting a RTL8192CU WiFi adapter, but that is a different story.  Many online tutorials use Ubuntu too.
http://elinux.org/Beagleboard:Ubuntu_On_BeagleBone_Black
I got a Ubuntu 13.10 Saucy build from Robert Nelson at http://rcn-ee.net/deb/flasher/
You WILL want to read the following page for flashing a new Linux distribution onto the BBB.
http://elinux.org/Beagleboard:Updating_The_Software
Then resize your microSD and use it as the boot device (the eMMC memory isn't enough for this project).

With Ubuntu installed, plug your BBB into your Linux computer (VM) again.  You will then be able to ssh into the BBB (ssh -l ubuntu 192.168.7.2 with password being temppwd.   Setup your usb-to-ethernet networking.  That being said, I hooked my ethernet cable up (since usb-to-ethernet was acting odd in Ubuntu) and waited for the BBB to show up on my network.  Then I ssh'd into it over eth0.

# sudo apt-get update
# sudo apt-get upgrade
# sudo apt-get install avahi-daemon

That last line will get Zeroconf installed so that we can access the BBB vi arm.local.  Of course, I changed the name of mine to astrobeagle in /etc/hostname and /etc/hosts.  Reboot.

Activate WiFi access
From what I have heard (November 2013), the Adafruit tutorial for getting WiFi working is not applicable to the BBB.  The dongle I purchased from them uses the RTL8192cu Chipset, and after a week's worth of compiling things on my own, here are the best instructions I have found on getting it to work:
http://wiesel.ece.utah.edu/redmine/projects/hacks/wiki/BeagleBone_Black_AP

My kernel is saucy 3.8.13-bone30, so I had to make adjustments as mentioned by Anh Long.  Additionally, for step 9 to compile the driver, I had to adjust the Makefile.  Having tried many approaches previously, I found some good info from Evan Hanau on fixes to the Makefile.  By default, the Makefile is setup to build for i386, so it needs to be switched to arm.

With wifi up and running, want to get hostapd running so that I can make the BBB into an access point.  Ahn's writeup is good.  After configuration and a reboot, I see my beaglebone as an access point with my iPhone!  Pointing Safari to http://192.168.4.1 (I used the suggested 4 subnet) I can see apache running.

Time to hook up a USB hub and get the webcam going...

Activate webcam
I chose the Logitech C300 webcam due to established support in Linux (link).  HD resolutions were not necessary for my purposes (I hope).  The shape and design of the C300 also lends itself to disassembly for eventually mounting on a guidescope.  [Edit: DO NOT get a Microsoft LifeCam Studio.  It has a bug that pull full bandwidth from the USB and will effectively disable your WiFi adapter on the hub.  Look at this list.]  Plug in the webcam and check to see if it is recognized:

# lsusb

Now, we need to get  a few things if you want to follow Derek Molloy's example vid
# apt-get install v4l-utils pkg-config libopencv-dev libv4l-dev uvccapture
OpenCV isn't necessary for my final project, only if you are wanting to do OpenCV stuff.  With that installed, you can run v4l2-ctl to get all sorts of information in the camera.  I found out that my autoexposure was turned on and creating trouble, so...

# v4l2-ctl --set-ctrl=exposure_auto_priority=0

You can use uvccapture to grab some still frames.  Since my webcam doesn't do h264, if you are following Derek's tutorial, I did the following since my output is in MJPEG format:

# ./capture -o > output.raw (then scp'd the output file to my Linux desktop for ffmpeg...)
# ffmpeg -f mjpeg -i output.raw tmp.mp4

Phase 2: Install astronomy software
for the next post...

Beaglebone Black and Astrophotography: Preamble

Background
Astrophotography has many aspects, depending on ones' goals.  In a simplistic categorization, astrophotography can be divided into two classes: wide-field, and narrow field.  In wide field astrophotography, wide angle lenses are used to capture large regions of the sky.  Frequently, digital cameras with large aperture lenses are used, and often tracking systems that match the Earth's rotation are not necessary since exposure times are short.  Photographic systems, be it cameras alone or digital imaging devices attached to telescopes, with smaller apertures may need tracking systems to avoid star trailing and/or to get more detail.  In narrow field astrophotography, typically when imaging faint deep space objects (DSOs), accurate tracking systems to match Earth's sidereal rate are necessary due to the requisite longer exposures.  Cameras need sufficient time (in the order of minutes) to capture enough photons from DSOs to resolve the distant objects, and any movement degrades the image quality.  Therefore, for high quality pictures, a sturdy photographic mount that accurately tracks celestial objects is necessary.  For this, I once built my own "barn door tracker" and got decent results with up to 55mm camera lenses and 60 second exposures.

Telescope mounts come in a few varieties, but the altazimuth (alt-az) and equatorial mount are perhaps most commonly known.  For my purposes, I will be focusing on the german equatorial mount (GEM) found in the Celestron Advanced VX.  For the GEM, an axis of rotation is aligned with the Earth's rotation axis.  If the telescope is then rotated around this axis at the same rate as the Earth's rotation, all objects will stay stationary in the telescope's view.  Accurate alignment with the celestial pole is therefore important for proper tracking, as well matching the earth's rotation speed.  A perfect polar alignment combined with perfectly matched mechanical rotation has the possibility of supporting indefinitely long photographic exposures without star trails.  Unfortunately, this is not possible.  Consequently, shorter photographs that don't exhibit noticeable star trailing are typically taken in astrophotography, and multiple images are "stacked" with computer software to produce an enhanced image.

One way to enable longer photographic exposure times without star trailing is to actively adjust the direction in which the telescope is pointed when deviations are experienced.  In this scenario, a "guide star" is used as a reference point, and the telescope is nudged in whichever direction necessary to maintain the relative position of the guide star in the field of view.  To that end, autoguiders were created - smaller scopes attached to a main scope who's duty it is to keep a guide star stationary in the view.  The autoguiders typically have a CCD (or other digital sensors) linked to a computer that analyzes the position of a star or stars.  If a deviation in position is observed, corrective motor signals are sent back to the telescope mount, often to a dedicated autoguider port, to reestablish the initial alignment.  This system requires an imaging device separate from the main photographic imager as well as an attached computer to make all the adjustments.

Telescope directional control with a microprocessor
Many modern telescope mounts come with attached, handheld control boxes for adjusting the aim of the telescope.  With the advent of "GoTo" systems, the control boxes contain microprocessors with positional information on a large number of celestial objects.  If a telescope mount with GoTo is accurately aligned, for instance a GEM with good polar alignment, a simple press of a few buttons can "slew" the telescope to view stars, planets, and DSOs.  "Hobbiest" microprocessor boards such as the Raspberry Pi have also been configured to control GoTo mounts, allowing for connections to popular software such as Stellarium for slewing.

Long exposure astrophotography requirements
1. Motorized telescope mount
2. Accurate polar alignment (or as accurate as possible)
3. Photographic camera with "Bulb" setting
4. Imaging telescope or long focal length camera lens
5. Guide scope or off-axis guider
6. Guide camera
7. Hardware for analyzing guide camera data and sending adjustments to mount
8. Power supply

Item 7 in the list has typically taken care of with a laptop PC, which adds a significant cost if one is not already available.  A table would likely also be desired to keep the laptop off of the ground, and USB/serial cables of sufficient length would be needed to connect the computer to the guide camera and motorized mount.  To me, this looked like a hassle, but I still wanted to produce some great astrophotographs.

Not (conveniently) having a laptop, and not really interested in buying one nor leaving one outside for log periods of time, I wanted to build a different solution.  Could a microprocessor take the place of the computer?  Having toyed with a MSP430, I knew it could be configured to control the telescope mount, but it would not have the processing power or connectivity for analyzing CCD/webcam images.  Next up from that I looked at the Arduino, and I came to a similar conclusion at the time.  The Raspberry Pi (RPi) on the other hand had some distinct advantages.  RPi can run Linux, and there are Linux software packages (specifically linguider, INDI, and open-phd-guiding) for controlling telescope mounts via autoguiding.  A thread at Cloudy Nights Telescope Reviews described a project to do just that.  While remote GoTo control was achieved with the RPi, the original author decided to move to a MK808 ARM® system since the RPi didn't have the desired processing power.  The MK808 system additionally needed a USB hub for a GPUSB Guide port interface and webcam, although it had built-in WiFi.  A main downside to this solution, in my opinion, was the lack of expansion via GPIO and the extra guide port interface.

It was at this point I learned about the Beaglebone Black (BBB).  While not dual-core like the MK808, I figured that the fast, 1GHz ARM® Cortex-A8 processor would be able to handle necessary image processing for my project.  The BBB also has a large number of configurable pins available for all sorts of expansion.  I recognized that I could build an equivalent Guide port interface onto the BBB, avoiding the GPUSB dongle.  However, since the BBB only has one host USB port, a separate USB hub would still be necessary to simultaneously use a WiFi adapter and webcam (at least until a USB or WiFi expansion cape becomes available for the BBB).  Moreover, the BBB has the possibility to use LCD and LED displays for visual feedback without the need of an external monitor, as is the case for the MK808.

And here starts my tale with the BBB.

Phase 1: Configuring the BBB
Phase 2: Building astronomy software
Phase 3: GPIO-based guide port interface
Phase 4: Autoguiding
Phase 5: Celebrate
Phase 6: Digital camera control
Phase 7: Cape with USB hub and guide port interface