topic Re: Projecting data correctly in Arcgis basemaps. in ArcGIS Online Questions

Projecting data correctly in Arcgis basemaps.

ClintonSpencer — Fri, 28 Oct 2011 21:46:06 GMT

I loaded some data onto the basemap, but it is off by about 100 feet. is there anyway to correct this? My data is in NAD27. Thanks.

Re: Projecting data correctly in Arcgis basemaps.

MikeMinami — Mon, 31 Oct 2011 21:01:47 GMT

What kind of data are you adding to your map?

Thanks,

Mike

Re: Projecting data correctly in Arcgis basemaps.

ClintonSpencer — Tue, 01 Nov 2011 13:08:45 GMT

I am trying to add zipped shapefiles.

Re: Projecting data correctly in Arcgis basemaps.

MikeMinami — Tue, 01 Nov 2011 15:48:07 GMT

it's probably best to transform your data into WGS84 Web Mercator Auxiliary sphere first.

Thanks,

Mike

Re: Projecting data correctly in Arcgis basemaps.

ClintonSpencer — Tue, 01 Nov 2011 18:04:36 GMT

Okay, so that got is close, but we're still off by about 20-30 feet. Is that typical?

Re: Projecting data correctly in Arcgis basemaps.

MikeMinami — Tue, 01 Nov 2011 19:50:27 GMT

Well, there is some rounding going on during conversion, but this offset seems too big. Do you have ArcGIS Desktop? When you display the shapefile in desktop over the same basemap data, do you see the same offset?

Can you share your shapefiles with us? Both the original and transformed versions? Perhaps you can clip out a small piece of it if the data is large.

Thanks,

Mike

Re: Projecting data correctly in Arcgis basemaps.

JimWatts — Wed, 02 Nov 2011 00:55:46 GMT

Hi,
We are having the same problem with the Bing basemaps near approximately 45 Degrees S latitude.
The original thought was that because of the mercator projection, we were seeing a 10 m offset in the Bing basemap, however, when we projected into the WGS84 Web Mercator sphere, the problem didn't go away. We know the shapefiles we have are correct because they match all other data sources. We are using ArcGIS Desktop (ArcINFO licence) Version 10.0. The original polygon layer that we are working with is in WGS_1984, and we are just using the "On the fly" projection to visualize those in the WGS 1984 Web Mercator projection. The points that are out by ~ 10 meters are in NZGD 2000 New Zealand Transverse Mercator. We have tried re-projecting the points and polygons to Web Mercator, but still see the same offset, so it is likely that the problem is the Basemap, not the points/polygons.

Is there a way to correct the offset in the Bing maps?

One thought was to rasterize the Bing map so we can use the "Shift" tool and put it into the correct orientation, however, we are unable to figure out how to do that.

Do you have any tips for doing this?

Cheers

Re: Projecting data correctly in Arcgis basemaps.

MikeMinami — Wed, 02 Nov 2011 15:26:49 GMT

Jim,

Are you seeing the 10m shift when displaying in ArcGIS Desktop? Or in ArcGIS.com map viewer? Or both?

Thanks,

Mike

Re: Projecting data correctly in Arcgis basemaps.

JimWatts — Wed, 02 Nov 2011 19:48:31 GMT

Hi Mike,

We are seeing the 10m shift displaying in ArcGIS Desktop. Haven't tried it in ArcGIS.com. Should I re-post this in the ArcGIS Desktop Forum?

Cheers

Jim

Re: Projecting data correctly in Arcgis basemaps.

MelitaKennedy — Wed, 02 Nov 2011 23:12:38 GMT

Hi Clinton,

When you converted to Web Mercator Aux Sphere, what transformation did you use between NAD27 and WGS84? Is the data in the lower 48 states, Alaska, Hawaii, or Canada? (Each has a 'best' transformation)

Thanks,
Melita

Re: Projecting data correctly in Arcgis basemaps.

MikeMinami — Thu, 03 Nov 2011 17:42:34 GMT

Jim,

I don't really have a good answer why you're seeing offsets. We can see some offsets too (on the order of 5m) in our imagery basemaps when comparing some control points from here http://www.linz.govt.nz/. With other points, we have perfect alignment. We did some visual comparisons based on some descriptions we found, like in the attached file. In some instances, Bing Maps appears to be correct, where our imagery is off, but it could be related to the particular area we're looking at.

Mike

Re: Projecting data correctly in Arcgis basemaps.

JimWatts — Fri, 04 Nov 2011 02:51:07 GMT

Hi Mike,

Thanks for your help. I am mainly confused as it seems that other people on these forums seem to have similar issues but seem to be able to correct them. All my offsets are in the same direction and are relatively the same distance from where they should be.

Thanks again.

Cheers

Jim