Thanks for your page, that's helpful to understand your question.
Our API focus on convert between two specified projections, I tested based on the page today like this:
PointShape point = new PointShape(-117, 30);
UnmanagedProj4Projection proj4 = new UnmanagedProj4Projection();
proj4.InternalProjectionParametersString = "+proj=longlat +datum=NAD27"; // that's maybe epsg 4267?
proj4.ExternalProjectionParametersString = "+proj=longlat +datum=NAD83"; // it looks like epsg 4269, but not the same
PointShape rPoint = proj4.ConvertToExternalProjection(point) as PointShape;
But it looks the result is incorrect.
The correct value should be like this:
I guess that's maybe because our wrapper don't support this conversion type, or maybe that's because we hadn't integrated the latest Proj4 version.
I am not sure about your scenario, do you think that's possible to use two specified projection? If so I think we can get a exact result with our API.
Wish that's helpful.