Here's a summary of the issue to date. New standard names to be used with coordinates variables for the geostationary projection have been proposed to resolve a problem with canonical units that exists with the standard names being used to date. This problem is a defect in the current version of CF (CF 1.7).
The current CF conventions specify that the rectangular coordinates for the geostationary projection are identified by the **`standard_name`** attributes **`projection_x_coordinate`** and **`projection_y_coordinate`**. The standard name table declares these standard names to have canonical units of meters. The CF convention regarding standard names specifies that the units for a variable with a given standard name must have units that are convertible to the canonical units for that standard name. This conversion must be a simple units conversion — length to length, volume to volume, etc. The coordinate values for the geostationary projection are angles and have units of degrees or radians. It is a defect to use **`standard_name`** attributes of **`projection_x_coordinate`** and **`projection_y_coordinate`** for such coordinate variables because units of angles are not directly convertible to units of length. The proposed correction for the defect is creation of two new standard names for use with the geostationary projection. The new standard names are **`projection_x_angular_coordinate`** and **`projection_y_angular_coordinate`**. These new names would have canonical units of radians. A number of commenters have said they approve of the change. Others have expressed reservations about impacts on those who have already implemented software based on the current version of CF that might not recognize the coordinate variables because it was expecting the old standard names. @magau asked if it might be possible to change the CF conventions regarding standard name canonical units or make some exception for these particular standard names to resolve the defect without specifying new standard names. @erget suggested that the reservations, while valid, should not prevent correction of the defect, as it would not invalidate files claiming adherence to CF 1.7 (or 1.8), and it should not be difficult for software to support the new standard names. People indicating approval so far are: @lllliso @JimBiardCics @steingod @JonathanGregory Randy Horne @mraspaud People indicating concerns so far are: @magau -- You are receiving this because you commented. Reply to this email directly or view it on GitHub: https://github.com/cf-convention/cf-conventions/issues/230#issuecomment-575788782 This list forwards relevant notifications from Github. It is distinct from [email protected], although if you do nothing, a subscription to the UCAR list will result in a subscription to this list. To unsubscribe from this list only, send a message to [email protected].
