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Thread: removing points from a surface

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    Default removing points from a surface

    I know i have done this before, it has just been a while.
    What is the proper way to remove points from a surface?

    I just want to remove/delete them so the contours generate without taking any information from those points. we have some odd things happening; contours sprouting off lines in some areas, so im hoping removing some excess points will help

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    AUGI Addict sinc's Avatar
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    Default Re: removing points from a surface

    We'd need more details, but...

    If you're talking about Cogo Points, those are usually added to a Surface by adding a Point Group to the Surface definition. Easiest way to remove unwanted points from the Surface is to remove those points from the Point Group definition and rebuild the Surface.

    You can also make sure you have "Points" turned on in your Surface Style display. Then you can use the "Edit Surface - Delete Points" option to select and remove them. I recommend only using this for deleting "extra" points, though, such as those added by "minimize flat areas". If the points are Cogo Points, I prefer to remove them from the Point Group in the Surface definition, rather than by using "Edit Surface - Delete Points".

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    Default Re: removing points from a surface

    I dont usually work on the civil3D drawings but the others are convinced the only way to deal with this is exploding the surface and deleting the extra lines. But I'm convinced that is a terrible idea...

    they are Cogo Points, i was litterally just selecting them and deleting them before. I assume this is not the same?

    I attached a couple examples of what the contour lines are doing. maybe this can help direct the question of whether deleting points is even the right approach.
    Attached Images Attached Images

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    AUGI Addict jpaulsen's Avatar
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    Default Re: removing points from a surface

    That looks like a valley. The points at the bottom of the valley are the same elevation as your contour so the contour runs right into them. Try lowering those (-8.0) points 0.01' that should cause the contour to split into two and run on both sides of the points.

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    AUGI Addict sinc's Avatar
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    Default Re: removing points from a surface

    Quote Originally Posted by JRBOURNE View Post
    they are Cogo Points, i was litterally just selecting them and deleting them before. I assume this is not the same?
    Cogo Points don't automatically go into surfaces; you have to add them to the surface definition. For example, by default, our templates have a "Surface Points" Point Group that is setup to include only the appropriate point codes - e.g., things like storm inverts are automatically excluded from the surface definition.

    Similarly, if you have Cogo Points that you don't want in the surface, you can just exclude them from the Point Group(s) that you add to the surface definition. Then those points will still be in the drawing, in case you need them in the future, but they won't be part of the surface.

    What are all those numbers in that first image? Is that where you have field shots? How did you get these shots? Did you have a GPS rover setup to continuously take shots?

    If so, that's probably why you see the contours doing what they're doing. It's part of the nature of a TIN. Contours that are created from a TIN look best when the underlying shots approximate a grid. If you have widely spaced lines, with lots of shots close together in the lines, then you create a lot of long, skinny triangles in your TIN. Those lead to lots of "jaggies" in contours. So you'd probably get better-looking surfaces if your field surveyor set the equipment to take more widely-spaced shots, and then tightened up the lines, so that the shots were more evenly-spaced.

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    Default Re: removing points from a surface

    @ jpaulson,

    just so i understand you correctly, do you mean change the elevation the points are set at from -8' to .01' ?

    @ sinc,

    Yea those are field shots, (i turned them off for the second image) it is actually a hydro survey of a river, so the boat drives along using sonar to constantly take depth readings. I dont think it should be hard to just set the computer to take less readings. I am wondering if there would be a relatively simple way to just use every third shot or something.

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    Default Re: removing points from a surface

    No I meant to change them to -8.01. This may not be your best solution if they are field shots. I didn't realize what they were when I made that suggestion. As a general rule I don't change field shots.

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    AUGI Addict sinc's Avatar
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    Default Re: removing points from a surface

    Quote Originally Posted by JRBOURNE View Post
    Yea those are field shots, (i turned them off for the second image) it is actually a hydro survey of a river, so the boat drives along using sonar to constantly take depth readings. I dont think it should be hard to just set the computer to take less readings. I am wondering if there would be a relatively simple way to just use every third shot or something.
    The easiest way I can think of to weed it down to every third shot would be to use Excel. There are a variety of ways to accomplish it there. For example, delete 2 out of 3 shots in Excel, then import the smaller point file. Or use Excel to add an additional text string to the description of every third shot, and use that text string to create a Point Group in C3D.

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    Default Re: removing points from a surface

    You could also create a new point file format that only imports every third point. http://screencast.com/t/YWQwNjgxYmYt

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    AUGI Addict sinc's Avatar
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    Default Re: removing points from a surface

    Thanks for the reminder... I forgot that option was in there.

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