VTP Software Tutorials

Tutorial 4: Using Paging Tilesets

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 free data from the USGS EarthExplorer and National Map, of a scenic spot called "Diamond Head" on the island of Oahu.
To save you from digging around the USGS sites, I have already downloaded and cropped some files to use:

• Elevation: oahu_dem_subset.tif (3.4 MB), a 10m DEM stored as a floating-point GeoTIFF
• Low-res satellite imagery: oahu_landsat_subset.tif, a small bit of LandSat (28m, which is very blurry)
• High-res aerial imagery: oahu_2010_diamond_head_30cm.tif (252 MB)
  • OR if you are constrained on bandwidth, you can use the reduced-resolution oahu_2010_diamond_head_60cm.tif (68 MB)

While this isn't a massive dataset, it is nonetheless large enough to demonstrate the process of using paging tilesets.

Step 1: Load and Examine the Data

Fortunately, the elevation and imagery are already in the same projection (coordinate system).

Launch VTBuilder, then drag and drop each file in: first the elevation, which should look like this:

Next, the satellite image:

Then the high-res aerial.  Note that because the image is large, by default, we don't display it; it stays on disk until we need to sample it.  This is called "out-of-core" access.  This is what allows you to sample from huge imagery, much more than your computer can hold at once.  It also makes dealing with big data faster, since only the extents are drawn:

 You can choose when images are handled out-of-core, in the Preference dialog (menu Project: Preferences).

Step 2: Choose Area and Tiling

Let's pick an area which will encompass the Diamond Head crater and some surrounding terrain.  You can pick any area with the Area Tool, or open the dialog (menu Area Tool: Numeric Values) and paste the following into the Origin and Size: (618989.2, 2349855.8), ( 7987.2, 9216.0)

Now let's think about what a good tiling would be for this data.  Menu: Area Tool: Match Area and Tiling to Layer:

As shown, choose the 30cm aerial as the layer we want to match. That's our highest-resolution data, we want to make sure we match it exactly, pixel-for-pixel.  To keep the number of tiles under control, we can go up to 2k tiles (Tile LOD0 Size: 2048).  That should result in 13 x 15 tiles.

If you are using the 60cm aerial instead, you can go with 1k tiles.  It will be the same number of tiles either way, but each tile will have fewer pixels.

When you ready, press OK. VTBuilder will very conveniently shifts the extents so that when we extract tiles, they will match our data precisely.

Step 2: Sample the Elevation

While our elevation isn't (in this example) big enough to need a tileset, we do need it as a set of tiles so that we can use it with the tiled imagery.  So, use the menu Area Tool: Sample Elevation to Tileset.

1. Choose a filename for the output, in the Elevation folder on your VTP data path.
2. Our elevation is much lower resolution than our imagery, so we can use just Size 256, 1 LOD:

You can see that this is still oversampling our 10m DEM at 2.4m (a 4x oversampling), but that's fine.  Press OK.  Say "no" to deriving image tiles (that would be very useful if we had no real imagery, but in this case we do).  VTBuilder will do the sampling and say "Successfully wrote" to your tileset.

Step 2: Sample the Imagery

Use the menu Area Tool: Sample Imagery to Tileset.

1. Choose a filename for the output, in the GeoSpecific folder on your VTP data path.
2. Now we go up to the full 2k per tile (or 1k with the lower-res aerial).  Note how the spacing of our most-detailed LOD matches the existing data (both 30 cm, or both 60 cm).
3. Use 4 LODs, as that will allow lower-res areas of our terrain to be smaller on disk:

Press OK.  VTBuilder will start working; it will take around 3 minutes depending on your machine.  A cool feature is that because we are using OpenGL to compress our images for us, you can see it working:

When finished, it will say "Successfully wrote".

Step 3: Describe your Terrain

Launch Enviro.  Create a new terrain and set the following in the Terrain Creation Parameters:

• Elevation: Grid Tiles: Tileset .ini file: diamond_head.ini
• Elevation: Grid Tiles: Check the option: Use multithreading for asynchronous tile loading.
• Texture: Tileset .ini file: diamond_head.ini

Step 4: Run

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.