DHI / DHI/mikecore-python

Projected to Geographical conversion breaks with Lambert_Conformal_Conic_2SP

Open
#26 2 comments 0 reactions 0 assignees View on GitHub
Dominant language
Python
Stars
5
Forks
1
PR merge metrics
No merged PRs in 30d

Description

Hi,

I had issues in mikeio when trying to create a Dfs2 file with a _Lambert_Conformal_Conic_2SP_ projection. I can do this succesfully when trying manually (i.e. in MIKE Zero GUI), and in mikecore. So I traced the issue to the `mikecore.projections.MapProjection` class used to setup the Dfs2 projection info for the Dfs2 builder: when it tries to convert projected coordinates it runs into numerical issues. See example below:

# Fail case: Lambert_Conformal_Conic_2SP projection
```python
from mikecore.Projections import MapProjection

# The projected and geographic coordinates here are the same
# This can be converted back and forth using the Datum Converter tool in MIKE Zero
origin_projected = [ -65900.32888812723, -678217.039068304]
origin_geographic = [ 24.01529,-34.987278]

# Custom projection string
proj_str = 'PROJCS["Custom",GEOGCS["Unused",DATUM["User defined",SPHEROID["WGS 1984",6378137,298.257223563]],'+\
'PRIMEM["Greenwich",0],UNIT["Degree",0.0174532925199433]],PROJECTION["Lambert_Conformal_Conic_2SP"],'+\
'PARAMETER["False_Easting",0],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",24.751587],'+\
'PARAMETER["Standard_Parallel_1",-40],PARAMETER["Standard_Parallel_2",-10],'+\
'PARAMETER["Latitude_Of_Origin",-28.702538],UNIT["Meter",1]]'

# Try conversion using MIKE MapProjection
proj_core = MapProjection.Create(proj_str)

# Projected to Geographic Fails
print(proj_core.Proj2Geo(*origin_projected))

# Geographic to Projected works
print(proj_core.Geo2Proj(*origin_geographic))

```
```shell
>>> (444.87039857071056, nan)
>>> (-65900.2668223073, -678217.0403999202)
```

As you can see the _Lambert_Conformal_Conic_2SP_ coordinate pairs fail when trying to converted from projected to geographical coordinates, while the reverse works just fine. I haven't tested this in the .NET/C# code, but I'm confident this isn't correct behaviour.

# Working case: Transverse_Mercator projection
```python
from mikecore.Projections import MapProjection

# Coordinate info
# The projected and geographic coordinates here are the same
# This can be converted back and forth using the Datum Converter tool in MIKE Zero
origin_projected = [ -89907.8133323,-3873624.5460040]
origin_geographic = [ 24.01529,-34.987278]

# Custom projection string
proj_str = 'PROJCS["WG25",GEOGCS["Unused",DATUM["User defined",SPHEROID["WGS 1984",6378137,298.257223563]],'+\
'PRIMEM["Greenwich",0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],'+\
'PARAMETER["False_Easting",0],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",25],PARAMETER["Scale_Factor",1],'+\
'PARAMETER["Latitude_Of_Origin",0],UNIT["Meter",1]]'

# Try conversion using MIKE MapProjection
proj_core = MapProjection.Create(proj_str)

# Projected to Geographic Fails
print(proj_core.Proj2Geo(*origin_projected))

# Geographic to Projected works
print(proj_core.Geo2Proj(*origin_geographic))

```
```shell
>>> (24.015290000000082, -34.9872779999965)
>>> (-89907.81333230426, -3873624.5460043526)
```
Success - works as expected!

Contributor guide

No contributing guide indexed for this repository

Assessment

This issue has not been assessed yet.

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.