topic Re: Datum in Coordinate Reference Systems Questions

Datum

ChuckTurlington — Tue, 04 Sep 2018 13:50:22 GMT

Hello,

I am using ArcMap 10.4.1.

I would like to match the datum between AutoCAD and ESRI ArcMap. However, I do not see the datum in the AutoCAD selections, comparing the WKT ESRI information and the AutoCAD options. The coordinate system I am looking for in ArcMap is designated as LL84 in AutoCAD, which is the WGS84 coordinate reference system, but do not see the flattening value matching. Is there a better way I can search for the correct datum/coordinate reference system that will match AutoCAD?

Re: Datum

DanPatterson_Retired — Tue, 04 Sep 2018 14:06:57 GMT

WGS 84: EPSG Projection -- Spatial Reference is a geographic coordinate system, aka unprojected

the inverse flattening is about 298

GEOGCS["WGS 84",

DATUM["WGS_1984",

SPHEROID["WGS 84",6378137,298.257223563, AUTHORITY["EPSG","7030"]], AUTHORITY["EPSG","6326"]],

PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]],

UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4326"]]

Re: Datum

ChuckTurlington — Tue, 04 Sep 2018 14:54:16 GMT

Dan,

Thanks again for your help. I did find the correct datum but I notice that the flattening is not the same as what Autodesk reports, see attached screen shots. However, the EPSG code matches and the imported aerial imagery appears to align with the site correctly. For my own understanding, is there a way I can search in ArcMap for the EPSG code when trying to match between Autocad or MicroStation to ESRI AcrMap?

Re: Datum

ChuckTurlington — Tue, 04 Sep 2018 14:56:41 GMT

Re: Datum

DanPatterson_Retired — Tue, 04 Sep 2018 15:48:09 GMT

Chuck

go to this link... there is one for projected coordinate systems as well

http://desktop.arcgis.com/en/arcmap/latest/map/projections/pdf/geographic_coordinate_systems.pdf