This page is out of date and needs to be updated and tools attached.

Source Data

Tins are pregenerated using a DEM file. the tin program will take in an upper left x and y coordinate, as well as a tile width. it will then go to the DEM file and grab all of the values that lie in those extents. once it has those values it runs 1 of two algorithms (specified in the command line), a max points or a significance point elimination.

POINT ELIMINATION

Both of these algorithms begin by giving a significance to each DEM point, significance is calculated by taking the perpendicular distance of each opposing point. max points takes the n maxpoints with the highest significance. significance drops anything below the significance value.

in order to match up the edges of the DEM files, the edge points are dropped in a separate pass. edge points do not take into consideration inner points, so that the same points will be dropped for the next tile over. in the tin generation program a maxpoints/sig value can be set for the inner points, and the edges.

see http://www.geog.ubc.ca/courses/klink/gis.notes/ncgia/u39.html#SEC39.2.2

we implement - 2. VIP (Very Important Points) Algorithm

TRIANGULATION

once the points have been dropped, the are then triangulated using fortunes algorithm.

STRIPING

next the triangles are organized into triangle strips, in order to improve performance. 4 algorithms are run against the triangles and the one with the least amount of separate strips is used. the 4 algorithms are GREEDY, GENEROUS, HYBRID, and LONGEST PATH

The first 3 are all similar, using a neighbor count to decide which triangle to move to next. GREEDY will move to the neighboring triangle with the most neighbors, etc.

Longest path starts from each triangle and uses recursive calls to find the longest path. once all triangles have been used the algorithm is comes to an end.

FILE FORMAT

A big-endian binary file is written in the following ordered manner:

UL_X double(8)
UL_Y double(8)
Width int(4)
NumPoints?? int(4)
-points float(4)*NumPoints?*3
NumStrips?? int(4)
-NumVerticies? int(4)*NumStrips?
--vertex_index int(4)*NumVerticies?