What's the Point of Grid Surfaces?

[OliverE]

Hi, 

Grid surfaces seem to have so many limitations compared to TIN surfaces. For example, the following are not permitted:

- pasting into another surface

- pasting another surface into the grid surface

- adding non-destructive boundaries

- creating cropped surfaces from them

- using most of the Edit Surface commands

- using the Data Shortcuts Manager to link/replace TIN surfaces with grid surfaces

- using the Data Shortcuts Manager to link/replace grid surfaces with other grid surfaces

I'm sure there's many more that I'm not aware of. It leaves me wondering what the purpose of grid surfaces are. Can anyone provide insight into when these surfaces are useful apart from purely displaying large surfaces that you don't plan to manipulate?

Cheers

C3D2021

Windows 10

[m_kingdon]

I think you answered you own question with "purely displaying large surfaces that you don't plan to manipulate".  This would be large existing ground data sets, aerial LIDAR etc that someone might design a stretch of highway / railway over.

To be honest, I have never encountered a grid surface in my career.  I think they might be somewhat of a legacy feature from early Civil 3D days.

[TerryDotson · Accepted solution]

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It leaves me wondering what the purpose of grid surfaces are.

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Just because Civil3D has a number of limitations regarding GridSurfaces doesn't mean they aren't useful and widely used outside of the Civil3D arena. 

1. Memory: In a TinSurface every point has to be stored with (3) doubles for X,Y,Z where a GridSurface only needs to store (1) double for the Z value, making it 3x more efficient in terms of memory and that's before you consider that TinSurfaces have to store an index of (3) long integers per triangle.  A TinSurface could easily take 5x the amount of memory.
2. Speed: To find the face for a random location in a TinSurface (without a special index) requires looping through thousands of points and doing double math which likely involves a SquareRoot calculation (slow).  This can be sped up with special indexes which burns more memory (on top of what's mentioned in item 1).  In contract in a GridSurface two simple divide operations (one for X, one for Y) tells you the cells row/col and you can find the values in the elevation array.
3. Appearance: This one is debate-able but contours from a TinSurface tend to look sharp and angular unless smoothing is applied.  The nature of a GridSurface tends to smooth out the data in the process of gridding.  That's a double edge sword when you need careful analysis of features like ditches and roads where TinSurfaces are best.
4. Usage: In the BIG world outside of Civil3D GridSurfaces are widely used.  Take Q(QIS) for example that does hundreds of functions with GridSurfaces in the name of Rasters, and has little to no support for TinSurfaces.

In summary, they both have their strengths and weaknesses, and both justify their existence.  To me a better argument would be that Civil3D needs to do more with GridSuraces than it does now.

[OliverE]

Hi Terry, thanks for the response. I should have made it more clear that I was enquiring about their uses within C3D. I'm aware they are a much more efficient surface model for the reasons you've mentioned, hence I'd like to utilize them in my workflows. However, as you stated, C3D doesn't seem to do much with grid surfaces and needs to include the ability to manipulate them in the same ways you can with TIN surfaces, otherwise I can't see much use for them other than displaying large surfaces. I was hoping I was missing something regarding their uses and functionality but seems like this isn't the case. Maybe I'll submit an idea.

[TerryDotson]

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Maybe I'll submit an idea.

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If there is any urgency, keep in mind that the 'desk isn't the only source of solutions. We were already looking into the ability to extract a bound subset of a GridSurface to a new surface.  Most of the things on your list look doable, it's just a question of who does them, and when.  If you're interested, contact me at dotson at dotsoft dot com.

[OliverE]

No urgency here. Would just be nice for Autodesk to include some more functionality with grid surfaces so we can make use of their efficiency while using them in our designs.

Cheers.

[neilyj666]

If it ain't to do with Cloud or collaboration then Autodesk aren't interested - it's the corporations with thousands of seats that drive the development