Project/transform from GCS_Sphere_ARC_INFO to WGS_1984_UTM_Zone_10N?

[Mattborski]

Is this transformation possible? When trying to use the Project tool, I get the following warning: "A datum transformation is expected, but the parameter is empty." This is the first I've dealt with Sphere_ARC_INFO as GCS and, oddly, there is not much info online about it. I'm wondering if I have to use Define Projection instead but, if so, what CS should I choose?

[DanPatterson]

GCS Sphere ARC INFO - ESRI:37008 (epsg.io)

GCS Sphere ARC INFO: ESRI Projection -- Spatial Reference

contains the coordinate information, I suspect that the datum transformation information requirement is because you are going from a sphere to a projected coordinate system with a defined datum.

What did the results look like? or what options were you offered for a transformation?

[Mattborski]

Thanks, Dan.

That's what threw me off actually. The tool didn't suggest, and wouldn't allow me to choose, a transformation option. I ran Project anyway and the features (line features for a river dataset) line up exactly the same as the original features. Turns out I found a better rivers layer anyway that had a datum that Arc allowed me to transform to WGS 84 so I used that, but I'm still curious about this one. I figured the defined datum would be as indicated below. My other layers that only had a GCS were able to be run through the Project tool just fine.

GEOGCS["GCS_Sphere_ARC_INFO",
    DATUM["Sphere_ARC_INFO",
        SPHEROID["Sphere_ARC_INFO",6370997,0]],
    PRIMEM["Greenwich",0],
    UNIT["Degree",0.017453292519943295],
    AUTHORITY["EPSG","37008"]]

[DanPatterson · Accepted solution]

I suspect it is because a sphere has no flattening, hence no datum transformation exists to ones that do, like WGS84

[Mattborski]

Ok. That makes sense. Whenever I feel like I have a grasp on transformations I get thrown a curve ball like this.

Thanks for the comments.