The C++ module NSGXnml is automatically installed on Windows and Linux via the repository. On macOS, the repository installs all applications except for NSGXnml. This is because installing NSGXnml on macOS requires some manual steps.
Download the correct NSGXnml zip file:
PixInsight 1.8.9-1: PI1.8.9-1-NSGXnml-pxm-1.0.4-mac.zip
PixInsight 1.8.9-2: PI1.8.9-2-NSGXnml-pxm-1.0.5-mac.zip
Note that you might get a warning. For example: "Blocked : uncommon file".
Accept and download anyway.
Unzip the contents (NSGXnml-pxm.dylib) to a permanent location (but don't use a PixInsight folder).
NSGXnml is unsigned, hence you need to:
In Finder, right-click on NSGXnml-pxm.dylib and select “Open”
When the error message pops up complaining about an unrecognized developer, click “Open”
A terminal window will pop up and almost immediately exit.
If you have installed an older version of NSGXnml, uninstall it from PixInsight:
PROCESS > Modules > Manage Modules...
Scroll down to the NSGXnml entry and deselect it.
Press 'Done'.
Restart PixInsight
Install NSGXnml:
In the PixInsight PROCESS menu, select:
PROCESS > Modules > Install Modules...
Browse to the folder.
Press "Search". A dialog should display "1 additional PixInsight module(s) were found..."
(You will need to select "Recursive" if the file is in a sub directory).
Press "Install".
A PixInsight bug has been reported for Mac OS that can affect the installation of all PI C++ modules (for example, StarNet2-pxm.dylib or NSGXnml-pxm.dylib). The following error can occur during installation:
Installing 1 module(s): /Users/name/PixInsight/NSGXnml-pxm.dylib <* failed *> *** Error: Unknown exception ** Warning: No modules were installed.
Work around: This error only occurs if you display the metadata for the C++ module while installing it. The problem only affects macOS.
The image below shows the "Install Modules" dialog without the metadata. The text area displays <No Module Selected> instead of the module metadata (description). Ignore the <No Module Selected> message, and press the "Install" button.
Don't click on the module (in this case the "E/PixInsightReleased/Windows1.8.9-2/bin/NSGXnml-pxm.dll" line); the text area would then display the module's metadata instead of <No Module Selected>.
If the install still fails, try reinstalling PixInsight.
Some users have reported that the install will only work if NSGXnml-pxm.dylib is placed within their home directory.