Different Geographic Projections from Two Files are Slightly Offset From Each Other

RE: Different Geographic Projections from Two Files are Slightly Offset From Each Other

Oto — Mon, 31 Jan 2022 09:04:43 GMT

You can easily do a Helmert translation if scale factor is the same.

https://communities.bentley.com/other/old_site_member_blogs/peer_blogs/b/marc_thomass_blog/posts/setting-up-in-the-real-world-georeferencing-update

https://communities.bentley.com/products/microstation/w/microstation__wiki/56125/helmert-transform

RE: Different Geographic Projections from Two Files are Slightly Offset From Each Other

David Hollner — Fri, 28 Jan 2022 18:21:14 GMT

We have it right now to test (I and one or two others have access to it), but we actually just moved to InRoads SS4 so it might not be given to us for a while.

Noted, though, thanks! I'll have to check it out.

RE: Different Geographic Projections from Two Files are Slightly Offset From Each Other

Lucas Hicks — Fri, 28 Jan 2022 18:14:43 GMT

Does anyone where you work have ORD? It has a translation tool for this kind of situation.

RE: Different Geographic Projections from Two Files are Slightly Offset From Each Other

David Hollner — Fri, 28 Jan 2022 18:08:01 GMT

[quote userid="5490" url="~/products/microstation/f/microstation-forum/225129/different-geographic-projections-from-two-files-are-slightly-offset-from-each-other/693871"]Have you spoken to the surveyor who did the survey[/quote]

This particular project, I'm personally not sure who it came from nor when the original survey was run. But I remember seeing this with another separate project or two recently where original survey under NAD27 projection didn't line up with newer survey with a NAD83 projection. Question's more generally-speaking than specific. Thanks for the response!

RE: Different Geographic Projections from Two Files are Slightly Offset From Each Other

David Hollner — Fri, 28 Jan 2022 17:57:32 GMT

[quote userid="5932" url="~/products/microstation/f/microstation-forum/225129/different-geographic-projections-from-two-files-are-slightly-offset-from-each-other/693824"]The average correction between NAD27 and NAD83 is an average of 0.349″ northward and 1.822″ eastward[/quote]

Hmm, that seems like it would make up most the difference. Question is now, is there a way to move the reference of the older survey that distance while keeping it as "Reprojected"?

I think ultimately I'll have to just make it Coincident to the original and reproject it manually. Thanks for the quote about the correction distance.

[quote userid="5932" url="~/products/microstation/f/microstation-forum/225129/different-geographic-projections-from-two-files-are-slightly-offset-from-each-other/693824"]But you could try EPSG:32015 for NAD27 as it has slightly different scale factor.[/quote]

I tried all other NY East projections that were in feet before posting. None made too much of a difference. One (probably that one) moved a fraction of an inch it seemed; not two feet.

RE: Different Geographic Projections from Two Files are Slightly Offset From Each Other

Lorys — Fri, 28 Jan 2022 05:58:51 GMT

[quote userid="318754" url="~/products/microstation/f/microstation-forum/225129/different-geographic-projections-from-two-files-are-slightly-offset-from-each-other"]One older survey uses an older state projected geographic coordinate system and the newer survey uses a newer projected GCS. When both are referenced into a mutual file (both Geographic-Reprojected), [/quote]

Have you spoken to the surveyor who did the survey they may be able to suggest a better datum with lower scale factor or they might do a better transformation for you...

RE: Different Geographic Projections from Two Files are Slightly Offset From Each Other

Oto — Thu, 27 Jan 2022 21:33:26 GMT

I read this: Depending on where you are in North America, NAD27 and NAD83 may differ in tens of meters for horizontal accuracy. The average correction between NAD27 and NAD83 is an average of 0.349″ northward and 1.822″ eastward

But you could try EPSG:32015 for NAD27 as it has slightly different scale factor.