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Clipping 3D Elevation data to void feature

PatGPatG Global Mapper UserPosts: 54Trusted User
edited February 2010 in Technical Support
I have a large 3D elevation low accuracy Geotiff that I need to merge with long linear irregular high accuracy data.

I have found that the combine terrain layers feathering options do not give me that great results and I now need to cut a void out of the large dataset that is bigger than my high accuracy data and then merge the two. This should then allow a smooth surface across the "gap" between them.

My question is how do I clip a void rather than crop a dataset? I want to remove the data inside a polygon rather than crop the data outside.

Is this possible in GM ver 11?

PatG

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2010
    Pat,

    You can do that by creating a large area covering your entire data set, then adding the desired void area as an island to that large area using the Digitizer Tool, then crop that area with the island for the void area when doing your export cropped to selected areas.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited February 2010
    Thanks Mike, that sounds like it will work but not as "cleanly" as I had hoped. I have noticed that when cropping to selected features the process is extremely slow. My polygon void has many vertices covering thousands of km. I cannot simplify it as the boundary is crucial to the data integrity. This sounds like it is not something that is possible to improve so we may have to live with it or find another way of doing it.

    Pat
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited February 2010
    Mike,
    I tried this method and found that GlobalMapper 11 does not honour my void boundary when creating the island in the large area shape. Please see attachments for an idea of what is happening. This makes this solution unworkable at the present time.

    01 is part of the area shape that I need to create as an island in the larger area. 02 is the result after applying the previous area as an island in the larger shape. This happens in many areas throughout the dataset. The island shape is contained entirely within the larger (rectangular shape).

    Any ideas as to why?

    Thanks for any assistance
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2010
    Pat,

    Ah, in this case the problem is that the area that you want to create as an island itself has islands in it. Since you can't have multiple levels of islands within an area, you lose the islands from the area being added as an island, so you just get the outer boundary of the selected area as a single island in the larger area. You would need to split your complex shape into pieces that don't have islands before add those pieces as islands into the larger area.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited February 2010
    (Thinking out loud.)

    This is a problematic workflow for us too.

    We often get beautifully fine data from a client for part of an area of interest, always an irregular part, and have to blend it into coarse data for the remainder.

    We have a workflow that involves creating an area representing the visible pixels in the fine surface, which we use to introduce feathering either in Manifold (using custom code executing on the GPU, very fast) or in Global Mapper (not as fast since using just the CPU).

    But I'm wondering whether there mightn't be a better workflow, which began by producing a raster mask for the fine-scale DEM, white pixels showing valid elevations and black pixels missing data. Its edges could then be heavily blurred, in Photoshop if necessary, and the mask exported back to a greyscale TIFF, which Global Mapper ought to be able to read as a DEM. What I'm looking for next is a way to use this mask to control the visibility of pixels in the fine-scale DEM, and thereby to control its blending with the coarse DEM.

    The main advantage of this workflow is in processing speed. GM blends two rasters much faster than it can use a polygon (or especially, a large set of complex polygons) to control feathering.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2010
    It sounds like what you are suggesting is basically creating a grayscale raster layer with the translucency value to apply to create the feather blending between an elevation layer and what is below it. That would be much faster once the initial grayscale raster layer was created, although of course it adds some additional complexity and the extra step of creating the raster mask layer in Photoshop.

    What you might try instead of this is selecting your mask area with the Digitizer Tool in Global Mapper, then right-clicking and selecting the option to simplify the area. This will allow you to remove vertices that don't significantly contribute to the shape. With how feather blending works you likely won't even notice a visual difference unless you really simplify it a ton, but having less vertices in the feather polygon will speed up the feathering process tremendously.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatGPatG Global Mapper User Posts: 54Trusted User
    edited February 2010
    Mike,
    This is obviously a technical issue with how GM software works. I have solved this problem by using Safe software's FME application. This worked flawlessy and extremely fast. Now I have a course DEM with voids larger than the high accuracy DEM that fits in. I can now merge the two and get a smooth interpolation along the edges.

    I'm just imagining the FME engine embedded in GlobalMapper. What a piece of software that would be!!! (but probably costly!).

    Not denigrating GM in any way here though. It's advantages far outweigh problems like this. Many thanks for your assistance Mike.

    TJHB,
    If you are not aware of FME you might like to investigate this piece of software. It's expensive but in our workflow, well worth it.
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited February 2010
    Thanks Pat. Yes, I would love FME, given the budget for it. Though might it stop me from learning to do things the hard way?

    Another piece of kit worth serious consideration is Geographic Imager from Avenza, which as of version 3.0 (released today) allows you to manipulate georeferenced DEMs in Photoshop, as well as georeferenced imagery. It's a lot more affordable than FME (being much more narrowly focussed), at $US699. The new release supports 64-bit Photoshop extremely well. So this will be the basis of this sort of workflow for me from now on—unless it gets easier in Global Mapper or Manifold.

    Mike, have you checked out Geographic Imager 3.0? In my opinion it's the first version that adds anything worth paying for, to the toolset in Global Mapper. It lacks most of what Global Mapper has, naturally. Its strength is in allowing you to use the whole power of Photoshop (and its many plugins) to manipulate geographic images and DEMs.

    E.g. for this workflow: load both DEMs separately; "mosaic" the fine DEM on top of the coarse DEM, as a separate Photoshop layer; select all visible pixels in the fine DEM, and make that selection into a mask for the same layer; then feather or blur the mask so that the fine DEM will blend gently into the coarse one.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2010
    I was not aware of the Geographic Imager product at all, although I don't even have Photoshop so it wouldn't really pop up on my radar. It does look like a good tool for Photoshop users. Hopefully as Global Mapper continues to get more functionality there will be less need for going to Photoshop to do things, but of course Global Mapper will likely never have the full suite of graphics tools that Photoshop has due to the more focused market (plus there are a lot more developers working for Adobe!).

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • STHSTH Global Mapper User Posts: 434Trusted User
    edited February 2010
    Thanks for reminding me of a new version of the Geographic Imager. I wasnt too satisified with version 2, however I will try the new v3 now and see if it handles for instance BigTiff-files. These files are not handled by photoshop - so I am curious if it can be handled after installing Geographic Imager.
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