Plate Solving is a powerful instrument that finds coordinates of an image being analysed.

You will find it very useful to find your target both with manual and automatic mounts.

To use the Plate Solving module, first you need to make sure you've loaded both the Astrometry and any telescope driver in your INDI Server. If you don't have an a GOTO mount, you can still use the Plate Solving module by selecting the Telescope Simulator driver.

Note: currently only the offline astrometry.net plate solving engine is supported. It is then necessary that you then setup the engine the first time, downloading the necessary indexes.

Astrometry and Telescope Simulator drivers enabled for Plate Solving

It is also important that you select the correct focal length of your telescope or lens in the Options section of the Telescope INDI Driver. You can use up to 6 different settings, which is useful if you have different telescopes or lenses, or if you use a focal reducer/multiplier.

Telescope focal length

The second important thing is to make sure you download some indexes for the Astrometry.net plate solver. AstroPhoto Plus will do this automatically for you, choosing the right indexes depending on your gear. You will only need to do this once (or if you change your gear, obviously).

Just go to the Settings page. You will notice there's a Plate Solving section.
Settings - Plate Solving

The Timeout for field solving setting is 600 seconds by default (10 minutes), and should be left as it is unless you have different requirements. Clicking the Download Astrometry.net index files button will open a new dialog.

Download Plate Solving Indexes dialog

Here you need to specify the minimum field of view that you will be using for your images. This corresponds to the combination of your smaller camera sensor, and longer focal length.

If you know this data, you can enter it manually either by specifying the field of view (in arcminutes), or the focal length and camera information (sensor width in mm, or sensor width in pixels plus pixel width in um).

Or (and this is the easy option) just connect your camera to automatically retrieve this information.

Clicking the Download button will start downloading indexes for you in the $HOME/AstroPhoto Plus/Astrometry.Net Data directory. Please do not remove this directory, or you will have to download indexes again.

Downloading indexes

We can now move to the Plate Solving page.

Plate Solving - set Field of View manually
Plate Solving - Solve camera shot enabled, and get Field of View from CCD information

The first element we see is the Telescope focal length.

If you have multiple telescopes, you will also see a button for each one, allowing you to specify which one you want to use.
Remember that if you have multiple profiles on your telescope driver you need to select the correct one in the INDI Device Page as specified above. Selecting the correct focal length is important to automatically calculate the field of view.

When multiple cameras are connected, you will also see a button for each camera, in order to select one.

Sync telescope on solve will automatically synchronise the telescope driver to the solved coordinates. If you have a Goto mount, this means your controller will know more precisely the current position, and moving the telescope will result in more precise pointing. With the Telescope Simulator driver, this will only update the current position. If you have an INDI compatible planetarium like KStars, you will be able to see where the Telescope Simulator is currently pointing in your sky map.

Next we have the Solve on camera shot button. When this is enabled, the sidebar will populate with options to shoot a new picture, like in the Camera page. The Plate Solving module will then automatically try to solve the new image as soon as the shot is finished.

Downsample image reduces the image resolution in order to get faster solving. The more you downsample, the faster the plate solving will be, however if you downsample too much the plate solver might not be able to recognize stars in your image. Use the default of 2 for most cameras. You can try reducing further if you have a very large sensor (with a full frame camera, try 4).

Finally you can specify the field of view. Off will try every possible field of view for which we have an index file. Manual will let you specify the minimum and maximum field of view (width) in arcminutes, while if you click the button corresponding to your camera, the field of view will be automatically calculated from camera and telescope information.

If you enabled the Solve camera shot option, all you have to do now is take a new image. If not, you can upload a FITS file to run the plate solving module against it. This will start the plate solving engine.

When a solution is found, you will see a table with a summary of the solved coordinates, field of view size and a link to the Aladin service, which will let you see the pointed coordinates in a high resolution imaging catalogue (this will require an internet connection).

A simple sky map will also be provided, with an indicator for the current solved position.

Plate Solving - solution found

Usually at this point you should move the telescope if it is not exactly pointing your target, and rerun the plate solving at each iteration until you get close enough to see your target in the field of your camera.

At this point, you can go back to the Camera page.