Polar Alignment without Polaris (workflow)

Discussions on extending SharpCap using the built in Python scripting functionality
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Polar Alignment without Polaris (workflow)

Post by fly_n »

Hello all,
using scripting in Sharpcap, plate solving and some math in R, I put together a workflow for myself on how to polar align without Polaris.

a) slew with Sharpcap to get regularly spaced pictures
b) use the same script to forward the pictures to plate solving and create a results file
c) fire up R to analyze the picture positions and calculate the offset in alignment
d) locate on a bright star
e) offset by the calculated value
f) manually recenter bright star
g) have fun (or redo to verify)

the scripts and a PDF in english can be found on the german astronomy forum:
https://forum.astronomie.de/threads/ein ... ow.283083/

If you find it interesting, drop me a note.
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Re: Polar Alignment without Polaris (workflow)

Post by admin »

Hi Norman,

What a great use of scripting! I think that you have basically put together a version of what might be called accelerated drift aligning where you use go to movements in the RA direction rather than the passage of time to bring out any drift in declination that might be resulting from incorrect polar alignment.

Cheers, Robin
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Re: Polar Alignment without Polaris (workflow)

Post by stelaras1 »

wow great

i'm also interested in drift alignment

i'll give it a try

thanks for sharing :)
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Location: Germany

Re: Polar Alignment without Polaris (workflow)

Post by Jean-Francois »

Hello Norman and Robin,

I test the script for the polar alignment.

I can say that it was not easy to set the different part of software together.
Norman, please note that German link of the script contains only the "slewer183.py" and "astro_v22.R" script.
But, the video (https://youtu.be/FYEBOxvo1qk) shows that you use 3 scripts.
From the video I copy (image by image) the missing script.

Do I have a good result ? ... no.
Something seems to be wrong in the script function "collect(v1, v2)".
When I open the resulting text file, I have the following:

Do you remark ? ... 179,7,-1,0000 in place of 179,7;-1,0000

I modify the script function in:

import csv
def collect(v1, v2) :
mypath = ("C:\\Astro\\Align_Pics\\%03d_%03d.apm") % (v1, v2)
global SIDE
plate = csv.reader(open(mypath, "rb"), delimiter = ",")
line_1 = next(plate)
line_2 = next(plate)

check = line_1[:3]
if check == '999' :
mytext = str(SIDE[v1]) + ";" + line_1[0] + ";" + line_1[1] + ";" + line_2[1] + ";" + line_2[2]
mytext2 = mytext.replace('.',',')

if check == '999' :
with open('C:\\Astro\\Align_Pics\\ps_positions.txt', "a") as myfile:
myfile.writelines(mytext2 + "\n")

I repeat with this modification ... but no good result.
The R script calculates the correction to several 10° ... My mount is not so bad oriented.
I have an EQ8 mount and I perform the 2 stars alignment followed by the polar alignment sequence of the mount.
In the last alignment, the mount mentions that the polar alignment is below 1 arcmin on both axis.

Additional question ?
Why do you program a script in R ? in place to stay in the Ironpython script ?
It makes the software use not really user friendly. (first a script A, then a script B, copy manually the values in a script C and start script C).

Do you have the intention to modify the scripts in "all in one" script ?
(I ask so then if you do, I will not start to do by myself ;) )

Other point ... your method use the mount movement for the setting of the polar angle.
I think that it could be better to use the live image on the camera directly in place of the mount movement (backslash error).
With the plate solve result, it is possible to calculate the displacement (direction and length) on the image itself.
The user can click on a star, the script insert a box at the wanted position, then the user adjust the mount until the star is centered in the box.
If the displacement is larger than the view, the script can repeat this several times.
(Like the method of King in the software Prism ... but it uses the stars near the polar star, what is not visible from my location)

Best regards,

Note: Norman, during reading your R-script, I remark that your location is very near to my location ... ~25 km.
A question for visualization of the script code ... how can I insert it ?
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