Plotting mixed (geographic and Cartesian) axes - Mercator projection on geographic axis?

Q&A
1

Hi!
I’m trying to plot longitude and latitude depth sections of seismicity across a map area that uses the Mercator projection. I can use two Cartesian axes for the longitude section, as the distance per degree is constant separation. However, as the distance per degree for the latitude axes changes, the Cartesian axes are not suitable.
Is it possible to set a projection for the geographic axis on the depth section? Below is the code that I’m using.

gmt plot -R0/800/-50d/-30d -JX5c/14d quakes.txt -C -Sc

Thanks!

2

Hi @MHead, you might find the gallery example at https://docs.generic-mapping-tools.org/latest/gallery/ex28.html#example-28 helpful. It’s about mixing UTM and lat/lon Geographic data on the same map, but you might be able to adapt it to your use case. Let us know if that helps.

3

Hi @weiji14, thanks so much for pointing me to that example.
I finally managed to produce the plot - I also needed to convert my lat/lon data to utm to ensure it didn’t plot linearly on the geographic axis.

  gmt basemap -R160/168/-50/-30 -Jm0.5c -Baf -BwE -X10.5
  gmt mapproject quakes.txt -R160/168/-50/-30 -Jm0.5c > quakes_utm.txt
  gmt basemap -R0/800/0/13.17 -Jx0.005c/1c -Baf -BsN
  gmt plot quakes_utm.txt -C -Sc -i2,1,4,3

Is there a quick and easy way that I can use the new utm data to produce the -R limits, rather than looking for the maximum value (i.e. 13.17)?

Thanks again!

4

Note you are using a Mercator projection, not UTM, and normally when people deal with UTM coordinates they are in meters. Your output is in degrees *0.5 cm. Se -Ju for UTM projection.