Full circle of earth meridian

Questions
1

  1. I cannot get the full circle with the spherical formula:

    ParametricPlot3D[ CoordinateTransform[“Spherical” → “Cartesian”, { 1, t, 0}], {t, 0, 2 Pi},AxesLabel->{x,y,z}]

produces the same half circle as:

ParametricPlot3D[ CoordinateTransform["Spherical" -> "Cartesian", { 1, t, 0}], {t, 0, Pi},AxesLabel->{x,y,z}]

  1. Another problem is with the equator (why only half circle?) :

    ParametricPlot3D[ CoordinateTransform[“Spherical” → “Cartesian”, { 1, Pi/2, t}], {t, 0, 2 Pi}, AxesLabel->{x,y,z}]

But the following can draw the equator:

ParametricPlot3D[ CoordinateTransform["Spherical" -> "Cartesian", { 1, Pi/2, t}], {t, -Pi, Pi}, AxesLabel->{x,y,z}]
2

It is because CoordinateTransform["Spherical" -> "Cartesian", {1, t, 0}] refuses numerical values of t not between 0 and Pi. You can bypass that with Evaluate:

ParametricPlot3D[
 Evaluate@CoordinateTransform[
   "Spherical" -> "Cartesian", {1, t, 0}], {t, 0, 2 Pi}, 
 AxesLabel -> {x, y, z}]

so that the coordinate transformation will be computed symbolically before the numerical check kicks in.
Similarly for longitudes:

ParametricPlot3D[
 CoordinateTransform[
  "Spherical" -> "Cartesian", {1, Pi/2, t}], {t, -Pi, Pi}, 
 AxesLabel -> {x, y, z}]