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Author Topic: geo-refrenced orthomosaic photos exported with wrong coordinates  (Read 1491 times)

majou

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geo-refrenced orthomosaic photos exported with wrong coordinates
« on: September 18, 2020, 10:00:06 PM »
Hi all,

I have a model of excavation site that is referenced with markers, of which the xyz values are given to match point on site. I have generated an ortho photo for the "top" view, choosing "geographic" projection option. exported as Tiff with World file. I imported the photo into Autocad Map 3d, and it fill right into place matching the surveyed location. setting in xy correct location i mean. with z being 0.

now, the problem occurs because I need ortho photos for elevations and sections of the same model.
what I did is, as an example:
I set the view to predefined "front" view, then process generating orthomosaic, I choose "planer" projection (because geographic is greyed out) and from te drop down menu I choose "Top", I keep other options to their default, I now have the image exported as Tiff with world file.
since it is an elevation (facade) view then the photo actually shows what the model looks like in alignment to xz axes.

when I import this into autocad Map 3d, it falls in the wrong location. and in the wrong rotation. so, it imports it in the xy plane, but still insert it in different location than my survey and of course it should be tilted 90 degrees into the xz plane.

How can I export such views with their right coordinates so that it is imported within the right coordinated too??
is that possible? if not, then what strategy can I follow to make use of these image in the way I need ? of course I can always change the view in autocad to be "front", change UCS to match it, import the image, and manually move it into the right place. but I believe there must be a smarter way to do this since Metashape already offers the tool of exporting geo-refrenced ortho images. in the mean time I am only able to make use of ortho images in the "top" view.

all advises are appreciated.

many thanks!

dpitman

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Re: geo-refrenced orthomosaic photos exported with wrong coordinates
« Reply #1 on: September 19, 2020, 07:00:15 PM »
Hi Majou,

I'm not familiar with AC Map3D, but for clients using AC Civil3D they usually want a mesh (3D Model) to work with xyz data on a project and not an orthomosaic.  Maybe that would work for you.  You could use a textured mesh if you want RGB if AC Map3D will accept that.

Dave
« Last Edit: September 19, 2020, 07:03:06 PM by dpitman »

Alexey Pasumansky

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Re: geo-refrenced orthomosaic photos exported with wrong coordinates
« Reply #2 on: September 19, 2020, 10:21:22 PM »
As far as I know, GeoTIFF may only contain image in Geographic/Projected system (i.e. top down view), therefore if you are using arbitrary/custom projection plane option, if cannot be transformed to the geographic projection, as the transformation between them is not stored in GeoTIFF.

So for the planar projection you are getting just X and Y coordinates for the point on the orthomosaic, which do not correspond to the real word coordinates. Therefore you might need to find a different way of completing this task, probably, there's some way in Autocad to manually define the projection plane of the imported orthomosaic.
Best regards,
Alexey Pasumansky,
Agisoft LLC

majou

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Re: geo-refrenced orthomosaic photos exported with wrong coordinates
« Reply #3 on: September 20, 2020, 01:21:16 AM »
Thank you Alexey and Dave, indeed it seems that I should find a way to import 3d model instead.

Arie

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Re: geo-refrenced orthomosaic photos exported with wrong coordinates
« Reply #4 on: September 21, 2020, 05:28:40 PM »
Hi again,
i'm not sure how well this works with Metashape, but you can generate topographic height contours and import them into AutoCAD. If Metashape creates proper 3D-polylines, it should give you a nice, simplified version of the excavation.
I know it is possible in Cloudcompare. You could also generate cross-sections, export them as polyline and use in CAD. I'll be happy to send you a link to that tool. I'm not sure if I can post it here.
Cheers!