I have gridded X and Y that are defined by lon = 20:0.25:379.75; lat = -90:0.25:89.75; X, Y = ndgrid(lon, lat). My goal is to create a Boolean array (named Index) the same size as X (or Y) and their values should be 1 if they are inside a polygon. That way I can apply it to my Variable grid like…

Not knowing what ndgrid does (or more importantly, where it’s defined), I think inW = [inpolygon((x, y), polygon; in=true, on=false, out=false) for x in lon, y in lat] should do what you want. In general, I haven’t seen very many strong use cases for “grids” in Julia, broadcasting and loops are ju…

you want to use GMT.jl and for other reasons as well) you should surface (or other GMT gridders) instead of ndgrid

[image] leon: Or this is only applicable to internal GMT stored grids? GMT stored grids is just a Julia type. I already pointed you to them . It has a G.z member that is a plain 2D array.

Ccing @Alexander-Barth here. I think ndgrid is the preferred gridding method by DIVAnd, am I right? I hope it will not be too much different from the surface function within GMT.

I’m not comparing numeric merits (don’t even know that ndgrid, I thought it was the Matlab one) but you are having difficulties with the type conversions that would not exist if you computed the grid with a GMT method in first place.

Next question: What is meshgrid? That’s not a Base function either. If X, Y = ndgrid(x, y) are matrices such that X[i, j] == x[i] and Y[i, j] == y[j] (or vice versa), this is a very wasteful way to store data. For languages like Matlab it might make sense to create large matrices to represent repea…

[image] gustaphe: In general, I haven’t seen very many strong use cases for “grids” in Julia I may be wrong, but from memory, some parametric 3D surface plots (using plotlyjs, pyplot, Makie, etc.) seem to require the creation of grids first?

@joa-quim , there may be job opportunities for a goldsmith and jewelry designer using Julia… :ring:

I think your understanding is correct. Basically ndgrid creates a matrix for both longitude and latitude. That way, the program knows the exact longitude and latitude values at each of the grid points. That said, I agree the Julia way is more efficient.

Plots.jl (which I’ve spent most of my time using) has plot(-2:0.1:2, 0:0.1:4, (x, y) -> exp(- x^2/4 - y^2/2)). Internally it might be using grids (depending on backend), which I would guess is at least not a bottleneck in the plotting flow, but at least you’re not required to drag the grids around a…

How to check if my gridded X and Y are inside a polygon?

General Usage

joa-quim November 1, 2021, 2:57pm 13

And I bet your gorgeous golden stripes, too.

Topic		Replies	Views
Overlaying a grid of colored squares onto a map in GMT New to Julia gmt	5	612	January 10, 2024
How to plot contour in an arbitrary shape of area? Visualization question , gmt	4	1395	September 9, 2021
Meshgrid function in Julia Numerics	35	26489	November 27, 2025
Efficiently check if points are contained in polygons Geo question	33	5716	September 27, 2024
Confusion on Creating Gridded Interpolations General Usage question , packages , interpolations	23	4929	January 8, 2022

How to check if my gridded X and Y are inside a polygon?

Related topics