Learning about SRIDs (and constructing geometries via SQL)

Bud

Edit: Mods, I suppose this post could be moved to the Data Management community (or whatever's appropriate).

What resources do you recommend for learning about SRIDs? SRIDs have always been a gap for me.

For example, when working with a FC using SQL, it's not clear to me if/when I would need to change the SRID for the output geometries.

• If I extract points from a line FC via an SQL query:
  When constructing the resulting points using SQL, should I use the original SRID from the lines, or do I need a new SRID since the geometry type has changed? (from lines to points)

select 
    objectid,
    --Side note: If anyone's wondering, this is why I convert to/from WKB: https://support.esri.com/en/Technical-Article/000011333
    sde.st_geomfromwkb(sde.st_asbinary(sde.st_startpoint(sde.st_geometryn(shape,1))),sde.st_srid(shape)) points_shape
    --                                                                                   🡅
    --Question: When constructing the resulting points, should I use the original SRID from the lines, 
    --    or do I need a new SRID since the geometry type has changed? (from lines to points)
from
    lines    --Note: The original SRID of the lines is 300051.

 

• Or, if I remove the M-dimension from lines via an SQL query:
  Do I need to use a different SRID when constructing the non-M-enabled geometries via SQL?

 

Thanks.

George Thompson

Thanks for catching the extra "0". Post updated.