# Finding the rectangular domain that covers an oblique area

My script looks like this (1st figure):

``````gmt pscoast -Bafg -JS36/90/30c -R-15/60/68/90 -Ggray -png pie
``````

I would like to make this a rectangular map instead, i.e. I have to provide a `-Rw/s/e/n+r`. To obtain this I do:

``````\$ gmt mapproject -JS36/90/30c -R-15/60/68/90 -Wn0/0
-1.85242110467        62.3326996594

\$ gmt mapproject -JS36/90/30c -R-15/60/68/90 -Wn1/1
126   80.9626773189
``````

and use this in `-R` (2nd figure):

``````gmt pscoast -Bafg -JS36/90/30c -R-1.85242110467/62.3326996594/126/80.9626773189+r -Ggray -png rectangular
``````

``````To output the rectangular domain that covers an oblique area as defined
by -R -J, append r, or use R to get the result in -Rw/e/s/n string format.
``````

I was hoping that this would give me the wanted `-R`:

``````\$ gmt mapproject -JS36/90/30c -R-15/60/68/90 -WR
-R-15/60/68/90
``````

But obviously this just gives me the input `-R`. I donâ€™t understand when `mapproject -Wr/R` would give valuable information. Am I misunderstanding the description of `mapproject -Wr/R`?

Is there any way of getting `-R-1.85242110467/62.3326996594/126/80.9626773189+r` out of `mapproject` given `-JS36/90/30c -R-15/60/68/90`?

1 Like

it says â€śobliqueâ€ť, that is, oblique Mercator, not stereographic. you are specifying JSâ€¦ = stereographic.

But thanks anyway, personally I liked the question.

Why mercator?

In gmt.conf oblique is defined as

``````This setting applies to â€śobliqueâ€ť projections, which in this context means
maps whose boundary is a rectangle not specified by meridians and parallels``````

yet another context I believe

while the examples on the `mapproject`'s manual page explicitly use oblique Mercator projection

Yes. Thanks. Iâ€™ll have a closer look at the docs. Canâ€™t understand why this is so confusing to me.

what I wrote was probably totally wrong.

you wrote:
I would like to make this a rectangular map instead, i.e. I have to provide a `-Rw/s/e/n+r`.

`mapproject`'s option `-WR` gives `-Rw/e/s/n`. This is rectangular but not oblique, so it returns a copy of your `-R-15/60/68/90`.

Note the difference: you want `-Rw/s/e/n+r` while `-WR` gives `-Rw/e/s/n`. `-WR` does not do what you want.

See new documentation and illustration for -W in mapproject at the dev version documentation.

1 Like

As Paul wrote, this is now implemented. And I can do this:

``````gmt mapproject -JS36/90/30c -R-15/60/68/90 -WE
-R-1.852421104674526/62.33269965938534/126/80.96267731894207+r
``````