# Does Generalize Support 3D?

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06-11-2016 07:19 AM
Occasional Contributor III

Trying to generalize some 3D lines, but it does not seem to obey the distance tolerance in the Z space. Documentation doesn't seem to say anything either way. Would like to confirm if the generalizer even supports 3D?  If not, any recommendations on simplifying a 3D line?

Actually trying to do this in FME, but it was simplifying the same way... so using an ArcGIS GP was going to be the backup plan until it appears to not obey Z values either. Running 10.4 at the moment.

Thanks a lot!

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15 Replies
MVP Legendary Contributor

I will say no... generalization in 2D has some application such as data simplification based on proximity or duplicates.

I think to generalize in the Z axis would be a bit more complicated since one would presumably have to perform the generalization in the xy directions first.

Now will there be a counter-point???

Occasional Contributor

Hi Dan,

Just found this discussion, and I have another application case where I would need 3D generalization. My customer maintains a road network and wants to print kilometrage on maps that can be used by car drivers and should be consistent with their trip meters. Since part of the network is in mountainous terrain, we decided to use 3D length derived from a 10m DGM and accumulate it in M values. In a first step, we get the Z component onto the road nethwork with the Interpolate Surface tool, so that we can calculate the 3D length. You might argue that this does not represent the "true" length of the road, but it is certainly closer to reality than the 2D length.

The tool densifies the road network with vertices at about every 10 m, blowing up the size of the dataset by about 100%. We now want to generalize the dataset to get rid of vertices that do not have an influence on 3D length and the M values - that is, vertices that fall on a straight line in 3D space (straight line in XY space and zero or constant slope).

My approach for now is this:

1. From the densified and 3D length calibrated road network, extract all vertices to points and add X, Y, Z, M attributes
2. Generalize the road network (all vertices on straight lines in the XY space will drop out)
3. Locate features along routes to get updated M values for the extracted vertices along the generalized routes
4. Determine the difference between M values before and after generalization - those points where the difference is greater than a tolerance value we need to add back (this is a subset of the points that dropped out before)
5. Re-calibrate the road network with its vertices plus the points identified in step 4 - this will add only the relevant vertices back

I still think that the Douglas Peucker algorithm should not be too difficult to be implemented in 3D space, so maybe I will give it a try some day as an alternative.

Occasional Contributor

I found what I was looking for. There is a Generalize3D method in the ArcObjects interface IPolycurve3D. It just hasn't been exposed in a toolbox tool.

Occasional Contributor III

Hi Dan, thanks for that information.

We are basically after simplification based on proximity. We have ~60,000 3D lines each varying from 1,500 to 6,000 feet long. Each of these lines has a vertex at each foot along it, that's a lot! So after running the current generalize tool, a line might go from 2,000 vertices to 100. We just need the line to stay within a tolerance of about 1/2 a foot.

Our drivers for this are:

1. The performance on this dataset in ArcMap and ArcScene is tremendously better.

2. We need to intersect these 3D lines with 3D multipatchs... that intersection GP tool works great but takes many, many hours when run on the non-generalized dataset. The multipatches that are intersecting these lines change often so we have a nightly job to recalculate the intersections.

That's our reasoning for this at least. Thanks again for the help and if you or anyone might have any recommendations to solve this issue, that would be much appreciated.

MVP Legendary Contributor

I am curious now.  Are your lines straight? or do they collectively follow a pattern?

I am thinking along the lines of your data forming a 3D array.  It is easy to determine points of departure in the z direction, then generalize in the x,y based on that, perhaps rather than generalizing in the xy, first.  If you have any more comments on the data form that would be interesting.

Occasional Contributor III

I think that  generalization in the Z axis is depend on

1. The interpolation method for DEM creation
2. cell size ( small cell size make your 3d line more smooth )

After create DEM make your line get elevation from DEM surface.

layer properties > base heights >elevation from surface > floating  on a custom surface

MVP Legendary Contributor

Abdullah...this is for vector, not raster

x,y,z data can be represented as either sparse or dense arrays and it is possible to generalize the array in the 3rd dimension, then extract those array elements that either deviate globally or sequentially from a specified value or within a range.

As a sparse array, you are not confined by a cell size which limits the spatial resolution to finite units since there is no requirement for equal locational spacing.

This type of analysis currently is the forte of analytical tools such as numpy, scipy, r etc which we are beginning to interface with arcmap.

Occasional Contributor III

Yes that logically for vector, look to Ryan Coodey Question,Dan.

" Trying to generalize some 3D lines"  is line Raster ??????

when you get elevation from survey points , you shouldn't waste any one of them

for example, If I have 5 survey points in one meter square and adjust my cell size to 1 meter , that is meaning wasting for survey.

you should make your cell size not have more than one point ( In 3d modeling application).

So you should be carious for cell size and make it small enough to don't contain more than one point, and it will make the Lines smooth as far as survey enables us.

I'm not talking about dividing a cell pixel after creation a raster or increase pixels without varies data, Dan

because its output will be same pixel value  and we will not see a difference.

MVP Legendary Contributor

They are working with vectors, so I am not sure of your point.  Rasters and arrays are two different data structures which might share a often similar outward appearance visually but can be completely different conceptually and structurally.