How Decimate TIN Nodes (3D Analyst) works
Decimate TIN Nodes constructs a new triangulated irregular network (TIN) that contains a subset of the nodes from an input TIN. It's a form of generalization that is useful for thinning oversampled data. It's also a means of simplifying a TIN for more efficient visualization. There are two decimation methods: ZTOLERANCE and COUNT.
The ZTOLERANCE-based decimation method uses an iterative algorithm to produce a TIN whose surface interpretation is vertically accurate to within the specified Z tolerance of the input. This means that any data node of the input TIN, when compared using linear interpolation against the output TIN, will deviate by no more than this amount. This method also supports an optional {max_nodes} value, which is a size constraint. The tool will halt if it discovers that it's unable to produce a TIN within this size that also honors the requested Z tolerance. The output will still be produced, but a warning is issued that it's not within the requested tolerance. The default is no limit; the size of the output TIN can potentially be as large as the input.
The COUNT-based decimation method is geared toward producing a TIN of a certain size. Its {max_nodes} parameter represents the desired number of nodes in the output TIN. The output isn't guaranteed to have exactly this number of nodes; it's more of a target, and the output will be approximately this size.
The option to copy over breaklines will take the breaklines from the input and enforce the same lines, without any generalization of them, in the output. Note, this is likely to produce a TIN with a node count higher than necessary to achieve the Z tolerance. It also operates independently of any specified {max_nodes} value. Use this only if your application requires it. The default is FALSE (breaklines will not be copied).
The data boundary of the output TIN will be enforced via breakline edges regardless of whether the option to copy breaklines has been used or even whether the input TIN data boundary is enforced with breakline edges. This may increase the size of the output TIN and operates independently of any specified {max_nodes} value.