As of APT V3.65.5 (beta), the problem described below has been resolved within APT itself.
Now, when the APT > Gear > JNOW" setting is selected it automatically converts the PlateSolve2 (PS2) and AllSkyPlateSolver (ASPS) communications to JNOW.
So:
- PS2/ASPS to APT is always J2000 (note: ASPS must be set to J2000)
- If APT JNOW is selected, then
- APT to planetarium s/w is transmitted as JNOW
- planetarium s/w to APT is transmitted as JNOW (note: planetarium must be set to JNOW)
- APT to PS2 is transmitted as J2000
- If APT JNOW is NOT selected, then
- APT to planetarium s/w is transmitted as J2000
- planetarium s/w to APT is transmitted as J2000 (note: planetarium must be set to J2000)
- APT to PS2 is transmitted as J2000
- "APT > Gear > JNOW" selected.
- "ASPS > settings > Platesolve settings > advanced > platesolver coordinates epoch" set to "J2000"
- "CdC > Setup > General > Server > Coordinate system to use with clients" set to "Current chart coordinate system"
- EQMOD set to JNOW (though apparently this doesn't matter)
The Problem
The problem starts with Platesolve2 (PS2). It provides it's solve data in J2000 epoch. Although there appears to be a PS2 setting (PS2 > View > Parameters > Default Catalog epoch) to change the coordinate system, it seems to make no difference to the result.
APT, acting as the middleware, can pass these coordinates on to Cartes du Ciel (CdC) for it to show (APT > Gear Tab > Point Craft > Show) as a rectangle of the appropriate Field of View and Orientation (CdC > Right Click > Finder Circle > Rectangle).
Image as shown in APT's Preview window
If CdC happens to be displaying in "Equatorial coordinates", with "type" set to "Mean J2000" then the rectangle is exactly the same as APT shows in it's preview window. The Chart coordinate system can be set here: CdC > Setup > Chart Coordinates > Chart coordinates system > Equatorial coordinates and Type of coordinates > Mean J2000
Solved FOV and Orientation Rectangle as shown correctly in CdC
However, as soon as CdC is set to display in "Alt-Az coordinates", it automatically changes the "Chart Coordinates" to "Azimuthal coordinates" with "type" set to "Apparent" (i.e. JNow). This means that the the displayed rectangle is offset, by at about 1arcmin as of 2019.
Solved FOV and Orientation Rectangle as shown incorrectly in CdC
Although APT can be set to use "JNow" (APT > Gear > JNow) it makes no difference to the CdC display because in this case it's just acting as middleware.
The Solution
Patrick Chevalley (CdC developer) and Ivo have collaborated to resolve this issue.
Patrick has kindly provided a setting in CdC that means that all communications with external applications (in this case APT) can be forced to use the J2000 epoch, irrespective of the coordinate system used for it's display. The CdC setting is under "CdC > Setup > General > Server tab > Coordinate system to use with clients > Force J2000"
For consistency, with PS2's epoch, the other requirements are that:
- All Sky Plate Solver (ASPS) is also set to use J2000: select "ASPS > Settings > Plate Solver Settings > Advanced > Plate Solver Coordinates epoch > J2000"
- EQMOD/EQASCOM (if you use it) is set to J2000
Notes
Note: It makes no difference to this setup whether APT is set to use "J2000" or "JNow" (APT > Gear tab > JNow). However, it's probably worth keeping all the coordinates the same, so deselect this option.
As of 21/01/2019 this option in CdC is only available in beta. For those that want to test it it can be found here: http://sourceforge.net/projects/skychar ... 019-01-21/.
Please note, this is a Beta version, so there is no guarantee it won't have issues. So it's use should be treated as such.
A final thanks to Patrick and Ivo for implementing this solution in only a couple of days!
He took the care completely in CdC!
