Geometry creation tutorial

[asinghvi17]

This PR adds a geometry creation tutorial plus some other doc improvements that sprang from there.

cc @alex-s-gardner

[asinghvi17]

https://juliageo.org/GeometryOps.jl/previews/PR151/tutorials/creating_geometry

[alex-s-gardner]

I tried to add an example where for plotting a polygon with a different CRS (EPSG:32611) on the same map as the tutorial by was unable to get it to work. I think this would be useful for showing how different CRS are interpreted

[alex-s-gardner]

I tried to add an example where for plotting a polygon with a different CRS (EPSG:32611) on the same map as the tutorial by was unable to get it to work. I think this would be useful for showing how different CRS are interpreted

This was my attempt, following on from the first mapping example:

# OK, now what if we want to plot geomitires that are in a diffent Coordinate Reference System (CRS?)

# lets create a polygon in the WGS 84 / UTM zone 10N coodinate system [EPSG:32610](https://epsg.io/32610)
crs2 = GFT.EPSG(32610)
dest = "+proj=natearth2"

# create new points 
r = 200;
k = 1000;
ϴ = 0:0.01:2pi
x = r .* (k + 1) .* cos.(ϴ) .- r .* cos.((k + 1) .* ϴ)
y = r .* (k + 1) .* sin.(ϴ) .- r .* sin.((k + 1) .* ϴ)

# now a `LinearRing`
ring3 = GI.LinearRing(Point.(zip(x, y)))

# now lets make the LineRing into a Polygon with new `CRS``
polygon3 = GI.Polygon([ring1]; crs=crs2)

# create a new `GeoAccess` with a new source `CRS1`
ga = GeoAxis(
    fig[1, 1];
    source=crs2,
    dest=dest,
    xticklabelsvisible=false,
    yticklabelsvisible=false,
);

[asinghvi17]

I don't see a definition for dest here - but there are a few examples in the GeoMakie docs that should help

[alex-s-gardner]

but there are a few examples in the GeoMakie docs that should help
I can't seem to find any example with "linked axes" for plotting multiple source CRS data on the same figure. Maybe this is not possible yet.

[rafaqz]

Ok now I read it all this is awesome! Really is something we need.

Thanks @asinghvi17 I should have written this a year ago

[asinghvi17]

hmm, the whole idea is to set the source kwarg. Something like:

using CairoMakie, GeoMakie
import GeoFormatTypes as GFT
using Interpolations # for Streamplot on gridded data if necessary

f(x::Point2{T}) where T = Point2{T}(
    10 * (2 * cos(2 * deg2rad(x[1]) + 3 * deg2rad(x[2] + 30)) ^ 2),
    20 * cos(6 * deg2rad(x[1]))
)

pole_longitude=177.5
pole_latitude=37.5
fig, ax, plt = streamplot(
    f, 311.9..391.1, -23.6..24.8;
    arrow_size = 6,
    source = "+proj=ob_tran +o_proj=latlon +o_lon_p=0 +o_lat_p=$(pole_latitude) +lon_0=$(180+pole_longitude) +to_meter=$(deg2rad(1) * 6378137.0)",
    axis = (;
        type = GeoAxis,
        title = "Streamplot",
    )
)
lp = lines!(ax, GeoMakie.coastlines(); source = GFT.EPSG(4326), linewidth = 0.5, color = :black, xautolimits = false, yautolimits = false)
translate!(lp, 0, 0, -1)
fig

https://geo.makie.org/dev/examples/cartopy/streamplot

[alex-s-gardner]

whole idea is to set the source kwarg

Got it, thanks!

[asinghvi17]

I guess that wasn't made clear in the GeoMakie docs. I'll add a doc page about GeoAxis, and I guess the "multiple CRS" example doesn't show it off very well :D

[alex-s-gardner]

Are there plans to have the source crs read directly from the geometries? It seems a bit silly that we keep associating crs info to the geometries but then they're not used by GeoMakie.

[skygering]

Love it!! I think the CRS part could use a little more polishing but I am happy we have such thorough documentation!

[alex-s-gardner]

@asinghvi17 is there a function for adding crs info to an existing geometry ... I was looking for something line setcrs

[asinghvi17]

I don't think we have anything like that yet. Probably better to just create a new geometry with the CRS, or GO.tuples(geom; crs = ...).

[alex-s-gardner]

Stupid codespace server crashed when I was about to submit my modification... off to meetings now. I will get you something in a few hours

[rafaqz]

It would be nice to be able to rebuild any geom with crs without needing to use the right constructor.

We could make rebuild here more public, or add setcrs like Rasters has

[alex-s-gardner]

Is it by design that GeoMakie unable to plot a Line but it can plot a LineString?

[asinghvi17]

I'm pretty sure that there was just no convert_arguments added for that on the Makie end. We could add that I guess, at least for single Lines.

How would you treat a vector of lines? Would it be continuous (as a LineString) or discontinuous (as individual linesegments)?

[alex-s-gardner]

add setcrs like Rasters

setcrs of addcrs is more intuitive than rebuild... I don't think most people will intuitively think of adding a crs as rebuilding a geometry

[alex-s-gardner]

How would you treat a vector of lines? Would it be continuous (as a LineString) or discontinuous (as individual linesegments)?

This is a question for @rafaqz

[alex-s-gardner]

Moving some additional thoughts from the PR back over to Slack

[rafaqz]

I imagine given a vector of lines we should plot each one separately.

[asinghvi17]

I just pushed some Line conversion methods to my GeoMakie PR. It's a bit inefficient, but should be fine.

[alex-s-gardner]

Let's merge this PR

[asinghvi17]

One last thing - I was going through this and figured we needed some anchor points, so added headers. I will merge for now, but if the headers seem unreasonable we can always change them!

Thanks a lot for the effort @alex-s-gardner (and @JuliaGeo/geometryops for the reviews :D )