How can I convert coordinates from global to local CS in Mechanical?

Pierre Thieffry

When I select an entity in Mechanical, I can choose a coordinate system to display coordinates in the selection information. Is there a way to do it by script?

Pierre Thieffry

Here's an example for converting coordinates to a local coordinate system. Pay attention to proper unit conversions. The example works on cartesian coordinate systems and would require little work to apply to cylindrical CS as well.

def convertToCS(coords,cs_name,convert=True):
    # Converts coordinates to a given coordinate system
    # If convert=True, 'coords' is assumed to be in users unit
    # If convert=False, 'coords' must be in meters
    import units

    # Retrieve conversion factor from current length unit to meters
    toUnit = "m" # Always generate the result to display in SI unit
    fromUnit=ExtAPI.DataModel.AnalysisList[0].CurrentConsistentUnitFromQuantityName("Length")
    convFact = units.ConvertUnit(1, fromUnit, toUnit, "Length")

    # Retrieve axis from coordinate system
    # Assume cs_name is unique (if not, the first one will be used)
    csM = ExtAPI.DataModel.GetObjectsByName(cs_name)[0]
    csXAxis = csM.XAxis
    csYAxis = csM.YAxis
    csZAxis = csM.ZAxis

    # Convert to 3D vectors
    xAxis = Vector3D(csXAxis[0], csXAxis[1], csXAxis[2])
    yAxis = Vector3D(csYAxis[0], csYAxis[1], csYAxis[2])
    zAxis = Vector3D(csZAxis[0], csZAxis[1], csZAxis[2])

    # create transformation matrix
    # We use a 4x4 matrix with rotation and translations
    idM  =  Matrix4D()
    transM = idM.CreateSystem(xAxis,yAxis,zAxis)
    # Transpose to ensure proper transformation from global to local
    transM.Transpose()

    # Translation part of the transformation matrix
    origin=csM.Origin # Origin will be in user units, so convert to m
    origin_transfd=transM.Transform(Vector3D(origin[0],origin[1],origin[2]))

    for i in range(0,3):
        transM[12+i]=-origin_transfd[i]

    # Now convert point to new CS
    # First convert to meters if needed
    if convert:
        vec=Vector3D(coords[0]*convFact, coords[1]*convFact, coords[2]*convFact)
    else:
        vec=Vector3D(coords[0], coords[1], coords[2])

    # Rotate
    vec_transfd=transM.Transform(vec)

    # Return new coordinates in user units
    if convert:
        invFact=1/convFact
        return [vec_transfd[0]*invFact,vec_transfd[1]*invFact,vec_transfd[2]*invFact]
    else:
        return [vec_transfd[0],vec_transfd[1],vec_transfd[2]]

# Test function on current selection's centroid 
cursel=ExtAPI.SelectionManager.CurrentSelection
# using convert=False in function call as Centroid is always in meters
print(convertToCS(cursel.Entities[0].Centroid,'myCS',False)) 

Landon Mitchell Kanner

Here are some similarly useful functions.