curvilinear_compute_rectangular_grid_on_extension does not result in grid with constant dx/dy

[veenstrajelmer]

Describe the bug
When generating a spherical mesh I would expect the edge length to be relatively constant. I request 4/60 degrees, which is approximately 40075/360/60*4=7.42 km. However, the edge lengths of the resulting grid vary from 3340 to 5515. This might be valid, but also the edge length varies over latitude which I think should not be the case.

To Reproduce

from meshkernel import MakeGridParameters, MeshKernel, ProjectionType
import dfm_tools as dfmt

#general settings
lon_min,lon_max,lat_min,lat_max = -8, 3, 46, 52
lon_res,lat_res = 4/60, 4/60 # 4 nautical miles, is approx 40075/360/60*4=7.42 km

figsize = (10,8)
crs = 'EPSG:4326'

# Create an instance of MakeGridParameters and set the values
make_grid_parameters = MakeGridParameters(angle=0.0,
                                          origin_x=lon_min,
                                          origin_y=lat_min,
                                          upper_right_x=lon_max,
                                          upper_right_y=lat_max,
                                          block_size_x=lon_res,
                                          block_size_y=lat_res)

mk = MeshKernel(projection=ProjectionType.SPHERICAL)
mk.curvilinear_compute_rectangular_grid_on_extension(make_grid_parameters)
mk.curvilinear_convert_to_mesh2d() #convert to ugrid/mesh2d

#write xugrid grid to netcdf
xu_grid_uds = dfmt.meshkernel_to_UgridDataset(mk, crs=crs)
netfile = 'test_grid_no_constant_edge_length.nc'
xu_grid_uds.ugrid.to_netcdf(netfile)
#TODO: grid has edge_length of 3340 to 5155 meters, should this not be more constant?

Expected behavior
A resolution of about 7400 meters and more constant over space.

Screenshots

Version info (please complete the following information):

• OS: Windows 10
• Version 3.0.0