Orthographic projection with no lines of Long/Lat

Q&A
1

I’m new to using GMT 6.40 and enjoy it very much.

In making an orthographic projection of the Earth I only want the equator presented on the result and no lines of longitude or latitude. How do I do it?

Here’s the code I use now;

gmt begin GMT_tut_5
gmt set GMT_THEME cookbook
gmt coast -Rg -JG-045/10/6i -Bag -Dc -A5000 -Gwhite -SDarkTurquoise
gmt end show

2

Hi @PDA123. Welcome to the GMT forum.

-Bag draws the graticule. To keep only the equator, use latitude gridlines every 90° and no longitude lines:

gmt begin GMT_tut_5
    gmt set GMT_THEME cookbook
    gmt coast -Rg -JG-45/10/6i -Dc -A5000 -Gwhite -SDarkTurquoise -Byg90
gmt end show

Lines fall at -90°, 0° and 90°, and the poles are just points, so only the equator shows.

3

Thank you. That works very well.

4

The -Byg90 approach makes sense for isolating the equator without drawing longitude lines. Since the longitude interval is omitted, only the latitude graticule is rendered, and the poles collapse to points in the orthographic projection, so the equator is all that remains visible. Good to know it worked for you, PDA123. This is a useful trick when you want a clean globe view without the full graticule cluttering the map.