View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0002056 | SkyChart | 1-Software | public | 19-01-18 11:45 | 19-01-21 20:24 |
| Reporter | Jim Hunt | Assigned To | Patrick Chevalley | ||
| Priority | normal | Severity | minor | Reproducibility | always |
| Status | resolved | Resolution | fixed | ||
| Platform | PC | OS | Windows | OS Version | 10 64bit |
| Target Version | 4.2 | ||||
| Summary | 0002056: Chart Coordinates won't stay set as "Mean J2000" | ||||
| Description | There is no way a J2000 coordinate type, when switching between Equatorial and Azimuthal coordinate systems. Is this a bug or a feature? The issue is that to keep CdC, Platesolve2 (PS2), All Sky Plate Solver (ASPS) and Astrophotography Tool (APT) all in sync, the only coordinate type they all support is J2000. Although I could just use "Equatorial coordinates" all the time, using "Azimuthal coordinates" is much more intuitive. The ideal solution would be for "Azimuthal coordinates" to support "J2000". The alternative is that when switching to "Equatorial coordinates" the previous setting (i.e. J2000) is maintained. Thanks, Jim | ||||
| Steps To Reproduce | Open "CdC > Setup > Chart Coordinates". Set "Chart coordinate system" as "Equatorial coordinates" and then set "Type of coordinates" to "Mean J2000 (mean equinox and epoch J2000)". Select "Apply" and "OK". Open "CdC > Setup > Chart Coordinates". Set "Chart coordinate system" as "Azimuthal coordinates" and the"Type of coordinates" automatically changes to "Apparent (true equator, equinox and epoch of data)". Reset "Chart coordinate system" as "Equatorial coordinates" and "Type of coordinates" remains set at "Apparent (true equator, equinox and epoch of data)" | ||||
| Tags | No tags attached. | ||||
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Sorry! "There is no way a J2000 coordinate type..." should read: "There is no way to maintain a J2000 coordinate type..." Thanks, Jim |
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This is a feature, the reset to apparent coordinates is done voluntarily because this is the only system that show the real position of the objects right now in the sky. It make no sens to draw a Alt/Az map for the current date with the object position at J2000. We probably take wrong habit the last few decades by using J2000 for everything because the difference was small, but now this can make more than 1 minute of difference for the hour angle and this will only increase with the time. But it is probably possible to improve the communication with the other software without changing the coordinates used for the chart. First, as you mention plate solver, there is no problem to load a plate solved FITS file with J2000 WCS, it can be draw in the chart with apparent coordinates. If you write your own interface with CdC there is a command GETCHARTEQSYS that return the current equinox used for the chart. Then it is easy to apply the precession for the coordinates received or send to CdC. The problem is with the applications you mention. If I understand they use the command like GETRA, GETDEC, SETRA, SETDEC and expect to use J2000 in every case. A way to solve that without involving the authors of this software is to add an option in Setup/General/Server to force J2000 for all the communication with the external software. Do you thing this can solve your issue? |
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Hi Patrick, Thanks very much for your superfast reply. Perhaps if I explain the background a little more it will help our understanding. APT controls the process of taking astrophotography images. APT can use PS2 (and ASPS) to platesolve these images. Once an image has been successfully solved, APT can then request CdC to display a rectangular Finder Circle that shows the exact location, size and orientation of the image, using the data from the platesolve. When comparing the CdC finder circle display with the image display in APT it has always been slightly out of alignment. The only solution, that consistently provides a match between APT and CdC, is to set both APT and CdC to J2000. For CdC this means using the Equatorial Coordinate view. APT can be set to use JNow coordinates. PS2 can be set to "Default Catalog Epoch = 2018", but this seems to make no difference. I really don't know whether your solution will help. My understanding just isn't good enough to understand the implications. I shall send Ivaylo Stoynov (APT's owner and developer) a link to this conversation to see if he can contribute. Ivo is very active in resolving issues and seems extremely happy to coordinate with other developers to improve any solution. Thanks again, Patrick! Cheers, Jim |
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Hello Patrick, Jim, It is Ivo here (one of the APT authors) :) I have just made some research and APT sends the Ra/Dec found by solving unchanged. So "what we get is what we get" as we don't have way to trigger changes in PS2 (PlateSolve2 made by PlaneWave)… I can experiment to convert the Ra/Dec to JNow before sending them to CdC, but we also have import of coordinates from CdC to APT. Is there way to determine what is the set epoch? In the moment am not sure if there is need to convert back from JNow to J2000 in order the GoTo++ to work properly. As temporary workaround I can send SETPROJ command to set the projection back to Equatorial, but does this restore the previously set epoch? Clear skies, Ivo |
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Hi Ivo, Thanks for looking into it. :-) If I understand your suggestion correctly, changing the projection back to Equatorial means I would lose the Azimuthal view. But it is the Azimuthal view I wish to maintain, as I find it easier to work with. Do you think Patrick's suggestion of "add an option in Setup/General/Server to force J2000 for all the communication with the external software" would work with APT? Would it stop APT getting the right coordinates from CdC for the GoTo++ to work? Or, if everything is working in J2000 would it all be consistent? In retrospect, I think Patrick's idea is more "universal", should any other external have the same issue. Perhaps it could be extended to a 3 way option. Something like: Set all Server communication to: o Current coordinate system o Force JNow o Force J2000 Thanks, Jim: |
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Hi Ivo, Thank you for your explanation, I better understand what APT need. Using SETPROJ to restore Equatorial do not necessarily set the epoch to J2000, in fact in Equatorial projection a user can set any epoch he want. I also think that using J2000 for communication between software is the best option. I can add the option as Jim suggest above with default to "Force J2000", so it work immediately with APT. In this case the command GETCHARTEQSYS return 2000.0 so this must not break existing application. If an application really need Jnow the user just need to check the corresponding box to get the old behavior. Maybe I will not include "Force JNow" because you can also use Jnow with equatorial projection if need, so this just add unneeded complexity. The only problem is it will need a new CdC version to fix the issue, this can probably be quickly available in the beta version and I plan a new stable version soon. |
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Hi Jim, Patrick, Definietly "Force J2000" will work for APT "out-of-the-box" :) I'm sure that both with Jim can help with the beta testing if there is need. Also if there is something I have to implement will make it with higer priority. APT is kind of middle level in this hierarchi, so for it there is no big difference if the epoch is J2000 or JNow. Important is both CdC and the telescope to talk for same epoch :) Have a nice weekend! Ivo |
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Hi Patrick, Ivo, You guys are awesome!!! I'm more than happy to do any testing you need, Patrick. Actually I usually run the latest beta's (for CdC, APT and PHD2 :-) ) anyway. What's the best/easiest way for me to know that a beta with this update is available? Just one thought about setting "Force J2000" as the default. Isn't it safer to maintain the current mechanism as the default and therefore less likely to cause you "bug reports"? If someone checks "Force J2000" and has a problem, then there is a clear indication of where that problem has likely come from. Ivo already has a section in his documentation on CdC, so adding i a note about this setting I'm sure would be OK. Thanks again for your time and patience. Cheers, Jim |
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I am working on that, if there is enough clouds this weekend I probably finish that for Monday new beta version. I automatically build new beta version the Monday because I work on the program mostly on the weekend. |
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OK, I keep the current behavior by default. The beta version is available from: https://sourceforge.net/projects/skychart/files/0-beta/2019-01-21/ You can select the new J2000 option from the menu Setup/General/Server Please let me know how this work. |
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Hi Patrick. The answer is is works perfectly. I know it's such a small thing in the scheme of things, but it makes a world of difference! I have attached three images; the 1st shows the captured image in APT, the 2nd shows the the CdC presentation in JNow coordinates and the 3rd shows it with "Force 2000" set. It's clear to see that 1 and 3 are are perfect match. Awesome. (Update: Ah! looks like I can't update the images, they are too big?) Thanks to both you guys again! Ivo, I'll write up a post for the APT forum and also the APT FB page. Patrick, do you want me to do something similar for the CdC forum or is it being here sufficient?? Thanks again. Cheers, Jim |
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Hi Patrick, Ivo, The write-up is here: http://aptforum.com/phpbb/viewtopic.php?f=20&t=2253&p=13900#p13900 Thanks, Jim |
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Thank you for your report, it look very good! You can post in the CdC forum if you want, it is good if more people learn about this issue and the solution. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 19-01-18 11:45 | Jim Hunt | New Issue | |
| 19-01-18 11:55 | Jim Hunt | Note Added: 0005248 | |
| 19-01-18 18:22 | Patrick Chevalley | Project | CCdciel => SkyChart |
| 19-01-18 19:13 | Patrick Chevalley | Assigned To | => Patrick Chevalley |
| 19-01-18 19:13 | Patrick Chevalley | Status | new => assigned |
| 19-01-18 19:13 | Patrick Chevalley | Category | General => 1-Software |
| 19-01-18 19:13 | Patrick Chevalley | Target Version | => 4.2 |
| 19-01-18 19:13 | Patrick Chevalley | Note Added: 0005249 | |
| 19-01-18 19:13 | Patrick Chevalley | Status | assigned => feedback |
| 19-01-18 19:45 | Jim Hunt | Note Added: 0005250 | |
| 19-01-18 19:45 | Jim Hunt | Status | feedback => assigned |
| 19-01-18 23:21 | Ivaylo Stoynov | Note Added: 0005251 | |
| 19-01-19 00:03 | Jim Hunt | Note Added: 0005252 | |
| 19-01-19 10:35 | Patrick Chevalley | Note Added: 0005253 | |
| 19-01-19 10:57 | Ivaylo Stoynov | Note Added: 0005254 | |
| 19-01-19 11:35 | Jim Hunt | Note Added: 0005255 | |
| 19-01-19 14:44 | Patrick Chevalley | Note Added: 0005256 | |
| 19-01-21 08:23 | Patrick Chevalley | Status | assigned => feedback |
| 19-01-21 08:23 | Patrick Chevalley | Note Added: 0005259 | |
| 19-01-21 15:41 | Jim Hunt | Note Added: 0005260 | |
| 19-01-21 15:41 | Jim Hunt | Status | feedback => assigned |
| 19-01-21 15:48 | Jim Hunt | Note Edited: 0005260 | |
| 19-01-21 17:15 | Jim Hunt | Note Added: 0005261 | |
| 19-01-21 20:24 | Patrick Chevalley | Status | assigned => resolved |
| 19-01-21 20:24 | Patrick Chevalley | Resolution | open => fixed |
| 19-01-21 20:24 | Patrick Chevalley | Note Added: 0005262 |
