3D Analyst Terrain to TIN resulting in z values that do not correspond with terrain

[StephanieSimpko]

Trying to create a TIN from a LiDAR terrain dataset.  I am using ArcGIS 9.3.1 with 3D Analyst extension enabled for processing LiDAR .las files.  I created a terrain with reasonable elevations for my project area in Illinois.  Elevations in my terrain range from a low of 515.25 - 584.18, but the TIN that is created from it has an elevation range from 1690.449 - 1918! 

I used "1" as the pyramid resolution z tolerance, which was also one of the pyramid z tolerances I used to create the terrain.  Used the default Maximum Number of Nodes of 5000000, and checked Clip to Extent.

I am able to create a reasonable raster from the terrain, but again, if I try to use the Raster to TIN tool, it results in the same elevation increase.

Has anyone come across this problem when you were still using ArcGIS 9.3.1?

Thanks,
Stephanie

[JeffreySwain]

Since your differences from  are a factor of 3.28, I believe that you are suffering from the meters to feet conversion factor.  Are the units matching up?  Was there a change indicated between the processing?  I would check the units that the elevations are in.

[StephanieSimpko]

The distance units for the LiDAR data is in survey feet.  I just checked the terrain properties, and maybe that's the problem.  Here are the properties:

Data Type: File Geodatabase Terrain Dataset
Location:  \\CENTRAL\Shared\D3\Shared\Everyone\GIS\Grundy Co LiDAR\Geodatabase\Prologis.gdb
Feature Dataset: Prologis_Terrain
Terrain: Prologis_Terrain
Z Range: 515.250000, 584.179993
Pyramid type: Z Tolerance
Pyramid levels: 2
Total points: 11174864
Needs to be built: FALSE

Projected Coordinate System:  NAD_1983_StatePlane_Illinois_East_FIPS_1201_Feet
Projection:  Transverse_Mercator
False_Easting: 984250.00000000
False_Northing: 0.00000000
Central_Meridian: -88.33333333
Scale_Factor: 0.99997500
Latitude_Of_Origin: 36.66666667
Linear Unit: Foot_US (0.304801)

Geographic Coordinate System: GCS_North_American_1983
Datum: D_North_American_1983
Prime Meridian: 0
Angular Unit: Degree

Did I do something wrong when creating the terrain?  I don't remember any prompts saying that the units were being changed when creating the terrain, but it's been a while since I created it.  I'll create a new one to see if I can find where it is changing the units.

Thanks,

[StephanieSimpko]

Resolved the problem!  I needed to modify the properties of the coordinate system of the terrain dataset.  When I selected NAVD_1988 as the vertical datum, the Linear Units are in meters, so I had to click the Modify button from the Z Coordinate System tab in the dataset's Properties box, and change the Linear Unit Name from "Meters" to "Foot_US".  Once I did this, I tried the Terrain to TIN tool, and it produced a TIN that makes sense! 

Thanks for the help! 

Stephanie