topic Re: Define Projection/Unknown Coordinate System in Coordinate Reference Systems Questions

Define Projection/Unknown Coordinate System

janel_day — Mon, 23 May 2022 20:21:04 GMT

@MelitaKennedy An issue that came up when I was working on the Geologic Mapping Template a long time ago at Esri has resurfaced. The issue had to do with providing a 'template geodatabase" that contained a feature dataset with a spatial reference of "Unknown Coordinate System" that would later be set by using the "Define Projection" tool. This was sometime around ArcGIS Desktop 9.3 or 10. I'm remembering this workflow was problematic, but I don't remember why.

Is there any way to refresh my memory as to why this workflow was problematic and/or if it's still problematic in ArcGIS Pro? My rough recollection is that the issue had something to do with the sort of "behind the scenes" math. Maybe with the Domain, Resolution and Tolerance values?

Re: Define Projection/Unknown Coordinate System

MelitaKennedy — Mon, 23 May 2022 20:36:13 GMT

Hi Janel,

A feature dataset and/or feature classes use a spatial reference. A spatial reference includes the coordinate system and xy/z/m extents and resolutions (also tolerances but those are less problematic). The extents and resolutions are extremely different if the coordinate systems are geographic versus projected. You can't really set it for one type and have it work for the other type. PCS can also be pretty different, particularly in the US where you may have feet versus meters which messes up the storage precision (resolutions) and the tolerances.

I remember we discussed but I can't remember what you ended up doing!

Melita

Re: Define Projection/Unknown Coordinate System

janel_day — Mon, 23 May 2022 20:44:55 GMT

Hi Melita,

Thanks for the quick response and the detail! For the Geologic Mapping Template, we ended up creating a tool in ModelBuilder that would create a new database and dataset. The spatial reference for that was defined through user input as a model parameter at the time the database was created. Current project has taken a similar direction in that we're working on a script to create the database and the user defines the projection at the time of creation. My recollection from our discussion is the reason we started down that path, but then I started to question my recollection since it's been so long.

Thanks again!

Janel