sgp mosaic questions

[iwols]

hi just a question on this,when i create a sequence of 4 panes when i try to run it ,it says a rotator is required is this correct,and when i finally have the images what software do you use to join them together thanks

[AngryDonkey]

When you create a mosaic with the Wizard each pane/target will receive a rotation angle to ensure that the images overlap in the way they are supposed to. You can see this angle when you open up each target's properties.

When SGP runs the sequence and centres a target (via platesolving) it also checks the image angle is within the set tolerance. For this it needs a rotator to be able to rotate the camera to the correct angle if it's off 

Luckily if you don't have one you can use the 'manual rotator' i.e. your hands to achieve this. You still have to set and connect this as if it was a 'real' rotator i.e. like your camera you have you select it from the drop down box and click the connect button. Now with this connected, when SGP centres the target, it will show a popup box if any angle adjustments are required and tell you by how much to rotate your camera.

This is the page in the manual that covers it:

http://mainsequencesoftware.com/Content/SGPHelp/SequenceGeneratorPro.html?ManualRotator.html

[symmetal]

When you click 'Create Sequence' using the mosaic wizard the next window that appears called 'Mosaic Sequence' has a tick box called 'Auto rotate or validate rotation on mosaic start'. By default this is enabled. If you untick this box, you will get a warning that rotation can't be validated but that's ok. You can then run the sequence without it stopping saying a rotator is required.

It's easiest for mosaics if you align a camera axis, horizontal or vertical, so that it's parallel with the RA movement of your mount. I normally select horizontal, and check by moving the scope in RA while taking short exposures using 'Frame and Focus'. The stars and/or their trails should move parallel to the top and bottom edge of the image.

Keeping this camera alignment setup, which you can repeat easily on other days, you can then do your mosaic. You need to bear in mind that the mosaic panels to the left and right of your centre panel will be rotated compared to the centre panel, depending on the declination of the target. At Dec zero there is no rotation and as the Dec increases the rotation will be larger. 

The auto rotation (or manual option) in SGP does not take account of this Dec dependant rotation (I don't think other mosaic software does either, unless anyone knows different ). It just ensures the same rotation angle relative to the RA direction for each panel (which you've already done by aligning a camera axis to RA). You may need to increase the overlap between your panels when your imaging a target at higher Dec to account for this. 

Here's a rough mosaic stitch of the Heart & Soul Nebulas at about 60 degrees declination showing the amount of rotation you will get.  Panels in a vertical direction are not rotated with respect to each other.

Alan

[AngryDonkey]

On 15/11/2018 at 17:14, symmetal said:

The auto rotation (or manual option) in SGP does not take account of this Dec dependant rotation

Good spot! I also noticed this a while ago and was wondering why this is not implemented. Has this been discussed in the SGP forum at all? I guess there are not that many mosaics worth taking closer to the pole (at least in the northern hemisphere) but even at your declination above it does make a fair difference.

I did actually start off manually adjusting the rotation angle on the individual targets to compensate for this but because I don't have a rotator, changing the camera angle on every target change just became too tedious and I stopped doing it. I haven't really though about it that much back then, I just assumed that the correction angle would just be the difference in RA between the mosaic centre and the panel centre, does that sound right?

(Edit: The PixInsight MosaicPlanner script has an option to adjust for these angles.)

[AngryDonkey]

To answer the second question of the original post, I have used PixInsight in the past because that is the software I already have. It did work well for me but is not the easiest process until you get used to it (also depends on how big the mosaic is as to how it's done). I've not used it myself but apparently AstroPixelProcessor is very good at creating mosaics and easy to use. Neither are free though.

[don4l]

I cannot answer the questions about SGP as I do everything manually.

 

I use The Gimp to assemble my frames into a single image.  There is a "Tool" called the "Unified Transform Tool" which allows you to move and rotate one image relative to another until.   You can then use a Layer Mask to blend them together to disguise any colour imbalances between your frames.

 

There is a package called APP available on trial which people recommend for mosaics - but I couldn't get it to run, so I cannot comment.

[symmetal]

4 hours ago, AngryDonkey said:

Good spot! I also noticed this a while ago and was wondering why this is not implemented. Has this been discussed in the SGP forum at all? I guess there are not that many mosaics worth taking closer to the pole (at least in the northern hemisphere) but even at your declination above it does make a fair difference.

I did actually start off manually adjusting the rotation angle on the individual targets to compensate for this but because I don't have a rotator, changing the camera angle on every target change just became too tedious and I stopped doing it. I haven't really though about it that much back then, I just assumed that the correction angle would just be the difference in RA between the mosaic centre and the panel centre, does that sound right?

(Edit: The PixInsight MosaicPlanner script has an option to adjust for these angles.)

There was a discussion between me and somebody on the forum a year or so ago on this very topic and they did ask others who did mosaics how they dealt with this but there was little response. 

Like you I thought of manually rotating each frame to correct this but as you say it's just too tedious. I think the rotation angle could be the RA offset angle * sin( Declination angle), as at zero Dec there is no rotation but I haven't worked it out to check. If you took a 4 panel mosaic centred on the Pole you would end up with each panel rotated 90 degrees although what SGP would say I'm not sure as the target RA angle is any number you like between 0 and 360 degrees. 

Ah! Good to see that PinInsight does acknowledge that the problem exists.  

I my previous post I did say about aligning the camera edge parallel to the RA movement when moving back and forth in RA. In reality the RA movement will describe a segment of a circle so it should be the tangent of the RA movement circle where it crosses the image central vertical axis should be parallel to the image top or bottom, but unless you're near the pole this circle segment can be considered as a straight line. 

[jmel]

Hi.

I realized this is an older thread, but am dealing with some rotation issues.

In SGP I'd like to set a tolerance of say 10 degrees in either direction that my plate solved rotation can be 'off'... I use manual rotation.

I then want to be able to use the framing and mosaic wizard to frame the target, but since I allow 20 percent overlap, and cross zenith with my shots, I wish to allow flipped images to be considered okay (+/- 180).

Is this possible?

I had a 4 panel mosaic that messed up on the 4th panel due to a rotation issue that I forgot to fix before imaging.

I had disabled rotation verification in the wizard because in the past it wanted me to adjust .5 degrees etc...and I was getting frustrated after multiple iterations. I ended up just realigning the camera to the same spot each night, except the last night. I lost my marking on the tube...

 

 

[symmetal]

Hi jmel,

The tolerence for rotation is set in the 'Control Panel/Plate Solve' tab. Set the rotator error to 10.0 in your case.

To allow +/- 180 to be acceptable click the cogwheel next to the target name in the target list, click the Rotate Camera tick box and enable the +/-180 option. The 'rotate camera to' angle specified there is the precise rotation angle but if you've set a 10 degree rotator error in the box above it will accept any value +/- 10 degrees from this precise angle as being acceptable.

Does this do what you want?  ?

Alan

[jmel]

Ah, so it's either my preferred 10 degrees variation OR it will allow flipping of the image after meridian flip?

I was hoping for both

[symmetal]

It will be both. You set your 10 degrees variation in the first box. In the second box if the precise rotation is say 45 degrees, SGP will take any camera rotation angle between 35 and 55 degrees as OK. If the +/- 180 is also selected in the second box it will also accept angles between 215 and 235 degrees as being OK too. 

This page from the SGP manual should explain it. If you don't have an automatic rotator it will still work as shown but will give you prompts to rotate the camera manually.

Alan

[jmel]

Perfect - I think for some reason I had both of these set to 180 before. I've had the prompts but I wanted to have a nice bit of "fudge room" in case I can't get it precisely to the .5 degree setting that it wants.

>< 

^kinda like that... a pie wedge on opposite sides so I have a little wiggle room as well as it accepting a flipped image.

From what you said then, I should be fine. I guess the descriptions on each box were not as clear to me.