This tutorial will walk you through one of the most powerful features of the VTP software: Tiled dataset (Tilesets) which can be used to visualize datasets that are far larger than your system's RAM.
We'll be using the Lake Tahoe data from USGS Lake Tahoe Data Clearinghouse. While this isn't a truly massive dataset, it is nonetheless large enough to demonstrate the benefits of using paging tilesets.
Go to the clearinghouse and download their 10m DEM file and MrSID DOQ. They offer various formats, which choice isn't important: VTBuilder can read (almost) every format. (Using the LandSat image would produce a prettier dataset, but it is only 3249x1525 in resolution, so it's not as good a test of large data support.)
We need some elevation and imagery which covers the same area. Fortunately, the elevation and imagery in this Tahoe dataset are already in the same projection (UTM zone 10, NAD27). Unfortunately, they have different extents:
- Elevation: Origin and Size: (736895, 4278545), (35160, 84300)
- Imagery: Origin and Size: (737399.8, 4289027), (34748, 63360)
For the purposes of this tutorial, we'll pick an area inside both extents, so that it is covered by both kinds of data:
- Subset: Origin and Size: (739120, 4290200), ( 30400, 62000)
Launch VTBuilder and import the elevation data. It should look like this:
If the colors are strange, it's possible that you got a version of the data for which vertical units aren't handled correctly, so that it thinks feet are meters, resulting in very high values. If so, you can correct this with menu Elevation: Scale Elevation:
0.3048
Menu Area Tool: Numeric Values. Paste the desired extents: (739120, 4290200), ( 30400, 62000) into the Origin and Size field, then press OK.
Menu Area Tool: Merge and Resample Elevation. Select Output: To folder of Tiles, then press Tile Options. Set the following:
- Tile output file: On your data path,
Elevation/tahoe.ini- Columns: 11
- Rows: 24
- LOD 0 Size: 256 + 1
- Number of LODs: 3
Notice how this divides the area up into a grid of approximately square tiles, which at full (Level 0) resolution are very close to the resolution of the original data (10 meters).
Press OK to close the Tile Options dialog, then OK again. VTBuilder will do the tiling and resampling.
MrSID is one of the few formats VTBuilder can't read directly, so you can use the free MrSID GeoViewer (or any other software you prefer) to convert the MrSID to a GeoTIFF. The full resolution is 34748 x 63360. Unless you really want to stress your machine, it is probably wise to incorporate a 2:1 resample at this point, along with reducing the area to the desired subset for a 15200 x 31000 image:
- left 739120, right 769520, bottom 4290200, top 4352200
As a RGB GeoTIFF, this is a 1.3 GB file.
Import this GeoTIFF into VTBuilder. If it asks you for a projection, this file is UTM, NAD27, Zone 10.
When it tells you the image is large and asks if you want to use out-of-memory access, say Yes.
Fortunately, the image has already been cropped to the desired area, so we don't need to crop it any further.
Menu Imagery: Export to Tiles.
- Tile output file: On your data path,
GeoSpecific/tahoe_doq.ini- Columns: 11
- Rows: 24
- LOD 0 Size: 1024
- Number of LODs: 4
- Texture Compression: OpenGL
Note that the number of Columns and Rows must match the values we used for the Elevation, but the resolution can be different - in this case, it is 4x higher. Press OK. VTBuilder will create and write the tiles, which should take around 8 minutes.
Launch Enviro. Create a new terrain and set the following in the Terrain Construction Parameters:
- Elevation: Grid Tiles: Tileset .ini file:
tahoe.ini- Elevation: Grid Tiles: Check the option: Use multithreading for asynchronous tile loading.
- Vertical Exaggeration:
1.30- Texture: Tileset .ini file:
tahoe_doq.ini
Press OK on the Startup dialog. Enviro will open its main window with a 3D view of your terrain. You should be able to fly around, with the terrain detail loading on the fly as needed.
