Straight lines appearing on print layout for ortho projection

Question

I've created an orthographic projection map, and have added it to a print layout. When I then add a lat/lon grid at 10 degree intervals I get straight lines across the image as well as the curved ones I want. I saw a response to a similar problem suggesting a white fill or making the grid polygons rather than lines, but can't see any options to do this. Here's where I am. It's especially puzzling because I previously created an orthographic image which was identical apart from the map source, and it worked perfectly. AFAIK I didn't do anything differently:

After more trying more options, I find that this only happens at certain orientations, which is strange. When my ortho projection is centred on 40N 15E or 40N 15W all appears fine. For 50W or 80W (which is the one I want) I get the horizontal lines. Here's the parameters I'm using for 50W:

+proj=ortho +lat_0=40 +lon_0=-50 +x_0=0 +y_0=0 +a=6371000 +b=6371000 +units=m +no_defs

Answer 1

With non planar projections, the layout Grid sometimes has hard times generating the coordinates. I guess the recommendations you have seen relative to using grid polygons refer to adding a vector grid layer in the map Layers, not as something generated by the Layouts.

The approach behind this is to import vector coordinate grids (from Natural Earth for instance) or generate a vector grid yourself. One thing you sometimes have to do in that case is to "clip those geometries to the hemisphere" you are looking at with your projection, in order to avoid lines to be displayed in front of the sphere instead of circling behind. (There is a 'clip to hemisphere' plugin for that)

Luckily, there is an even simpler plugin called Build Globe View which does all that in one click : you can use it to generate the relevant vector grid, centered on the current view (your custom projection)

Creating the graticule grid, 10 degrees, centered on your projection:

From there, the Layout will display the grid as part of your map Layers (and therefore tune the grid rendering from the "Graticule" map layer):

In your case, just generate the Graticule grid as a layer in front of your earth layer and you should be fine.