topic Re: Are there differences with ESRI geolocation services and other services? in AEC (Architecture, Engineering and Construction) Questions

Are there differences with ESRI geolocation services and other services?

MauricioMartinez — Thu, 01 Oct 2020 19:47:08 GMT

I have an issue when exporting CAD files to ArcMap. The CAD software I use is Autocad Civil 3D (2019) and as some of you may know, it has a geolocation tool where you input the coordinates system you are workig with, and then it displays an online map (provided by BING).

Problem happens after I have been working on such map to create a series of poligons, when I export the polygons to ArcMap these are not in the same position as shown in Autocad, instead they are displaced a meter or so (using for this one of the BaseMaps provided by ESRI).

Is there an explanation of why this happens?

Re: Are there differences with ESRI geolocation services and other services?

HamedFarzin — Thu, 01 Oct 2020 22:11:42 GMT

Hi Mauricio Martinez,

You may have a different coordinate system between your CAD data and base map and need to apply a transformer, refer to this How To: Apply a geographic (datum) transformation in ArcMap .

Hope it helps!

Cheers,

Hamed

Re: Are there differences with ESRI geolocation services and other services?

JoshuaBixby — Thu, 01 Oct 2020 22:19:02 GMT

when I export the polygons to ArcMap these are not in the same position as shown in Autocad,

What are you comparing, specifically, to come to the conclusion they aren't in the same place? Are the polygons in shifted from background imagery, or are the new polygons shifted from the same data layers you have in Autocad?

Re: Are there differences with ESRI geolocation services and other services?

MauricioMartinez — Fri, 02 Oct 2020 18:00:56 GMT

Thank you.

The polygons are shifted from the background, they are in the same place (meaning the polygons), and what is changed are the background images of both programs.

Re: Are there differences with ESRI geolocation services and other services?

MauricioMartinez — Fri, 02 Oct 2020 18:24:45 GMT

Thank you Hamed.

My CAD data have the C.S. (UTM 13N WGS84) so I exported this to Shape with the same one... and wich Transformation should I select if the BaseMap has de C.S. : WGS 1984 Web Mercator Auxiliary Sphere?

Cheers.

Re: Are there differences with ESRI geolocation services and other services?

JoshuaBixby — Fri, 02 Oct 2020 22:10:29 GMT

The positional accuracy of "freely available" online imagery, e.g., Google Maps imagery or Bing Maps imagery, is seldomly better than 1 meter. The positional accuracy of the imagery is not related to its pixel resolution, but it is common for people to think that sub-foot/sub-30cm must be spatially accurate because it is so crisp. It is completely possible, and some would argue likely, that creating a polygon based on tracing features from one imagery source will shift at least a meter when overlaid on top of a different imagery source of the same area.