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Merged Image has shifted from original

MichaelGilham
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Hi,

I'm attempting to consolidate a series of images into a single image using Descartes 08.11.09.578 stand-alone version.

The series are TIFF files with sister data files. The image quality appears to be 1 pixel per 1 meter.

The DGN has a coordinate system attached.

When I use the merge tool, selecting a shape as the focus area, the resulting image is slightly shifted (in both X and Y) from the original. I've tried a number of different Resolution Options, and get a shift as the result of each - though the sift value may be different dependant on the option. And the sift is in the order of 0.25 to 0.7m. The goal is to produce an ECW at the same resolution as the original TIFF files.

I initially set the Resolution Option to Existing Raster, so the software reads the current resolution, and then change the option to another setting (e.g. Pixel size & scale), without changing any values, before creating the output ECW. I have tried using the Existing Raster setting when creating the output - I get a similar shifted result.

I have tried to output as a GEOTIFF and still get a shifted result.

I've also tried the corridor tool - using the same shape as the before and after shape - and still get a shifted result.

Any ideas??

Thanks in advance.

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    Hi Michael,

    The shift probably occurs because the border of the area you have selected resulted in a merged raster whose pixels are not aligned with the pixels of the original images.  

    There might also be caused if the pixels of your images are aligned together of if the resolution differs.

    If the pixels of your images are aligned, the solution is to try to select an merge area that match the border of pixels.

    You can see the border of the pixels by activating the Display Pixel Grid preference. Note that for performance reason the pixel grid is only displayed at high resolution (i.e. : when you zoom in the raster).

    Thanks,

    Mathieu



    Answer Verified By: MichaelGilham 

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    Try using the Corridor company.  With the corridor command you will need to place an element around your raster images that you want to combine to create one output image.  

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    Hi Mathieu,
     
    I had originally attempted to line the merge shape up with the pixel edges, in case that issue you described was the problem. I've since enabled the pixel grid, which allowed me to get the shapes much closer to the grid corners (the UORs didn't allow me to get exactly onto the grid corners), and have re-merged the images which significantly better results. I cannot see any shift at all now.
    Thank you for that excellent tip.
     
    fmcallis: Thanks for the tip but, as mentioned in my original post, I'd already tried the corridor tool with the same result.
    It seems that having the merge shape line up, as close as possible, with the pixel grid was the ticket.
     
    Thanks guys,
    Michael
     
    From: Mathieu St-pierre [mailto:bounce-Mathieu_St-pierre@communities.bentley.com]
    Sent: Tuesday, 8 July 2014 3:25 AM
    To: 3DImagingandPointCloudSoftware@communities.bentley.com
    Subject: RE: [3D Imaging and Point Cloud Software Forum] Merged Image has shifted from original
     
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    Replying to this email posts your reply in the thread.
     

    Hi Michael,

    The shift probably occurs because the border of the area you have selected resulted in a merged raster whose pixels are not aligned with the pixels of the original images.  

    There might also be caused if the pixels of your images are aligned together of if the resolution differs.

    If the pixels of your images are aligned, the solution is to try to select an merge area that match the border of pixels.

    You can see the border of the pixels by activating the Display Pixel Grid preference. Note that for performance reason the pixel grid is only displayed at high resolution (i.e. : when you zoom in the raster).

    Thanks,

    Mathieu

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