Getting Started
with VNS 3: Terrain
Basics
Part 3B. Tiling & Layers
1. After data import is complete,
save the project and go to the Render Task Mode. Open
the YNP Camera and rename it Main.
2. Use Edit Next 
on the editor titlebar to move to the YNP Planimetric
camera and rename it Plan.
3. Open the Main view,
Plan view, and Database Editor.
4. Open the Plan Camera
View Preferences to the Terrain page and check
the Terrain Polygon Edges box.
5. Use the + key or mouse
scroll wheel to zoom into the wireframe representation of the
3D terrain surface. It's a grid of regularly spaced georeferenced
points, each with an elevation.
6. Go to the Database Editor. Along with its new look and tabular
organization, you can undock  and
expand the window. You'll need to resize it again before docking
it. Turn to the Extent page. Slide right to the NS
Grid and EW Grid columns. The grid size is 10 m by
10 m. 10-meter DEMs are sometimes referred to as having a 10-meter
resolution. At render time, grid cells are divided into triangular
polygons. The degree of polygon subdivision is determined by
the Maximum Fractal Depth. The Plan grid with the square
cells divided into 2 triangles represents a Maximum Fractal Depth
of 0.
7. Return the Plan Camera
to its default  location.
Uncheck the Terrain Polygon Edges box in the View Preferences window and close it.
8. Alt-click the Main
Camera to activate it and Crtl-click a new location in
the drainage about here.
9. Give it an elevation of
2100 meters.
10. Render a preview.
11. Depending on the amount of
RAM you have, one of 2 things will happen. VNS will either take
some time to think about it and start rendering and or give you
a Memory Allocation Failure error.
12. To save time, VNS only renders
the DEMs it has to. In this project, our Main camera is
only seeing a part of the total terrain. Since we only have 1
DEM, VNS has to make calculations for the entire DEM, which is
a big waste of time and memory. The solution is to tile the DEM,
that is, subdivide it into several smaller DEMs. VNS will only
have to render what the camera sees, resulting in fewer calculations
and faster render times. Tiling is done during import for most
data types but the gap-filling required by the SDTS DEM format
precludes it. SDTS DEMs require a second import to tile the single
DEM created by the first import.
13. Open the Import Wizard  . Choose
the YNP-10m.elev we just created, and Open it.
14. Next your way through
the Import
Wizard to the DATA POSITIONING
window. Previously, this is where we accepted defaults and imported.
We could do this now and the DEM would be tiled automatically,
but we'd like to see what the Wizard is doing. Select Change
Settings.
15. Click Next until you
get to the OUTPUT DEMS page. The information box at the top explains
tiling, telling us the render engine has to load an entire DEM
into memory if any portion of the DEM is in camera view. The
Import
Wizard chooses DEMs Row-Wise
and Column-Wise to divide the imported DEM into 300-row by 300-column
tiles. That's where the 7 and 10 come from. We're not going to
change anything so Import.
16. If you select an Object
in the Database to refresh the list, you'll notice that we now
have 75 objects. That's 4 quad boundary vectors, 70 tiled DEMs
(10 rows times 7 columns), and the original DEM.
17. Select the original YNP-10m
DEM at the bottom of the list. That makes it the active object,
so it's partially highlighted in the Main view where it overlaps
matching DEM tiles. If we don't disable or remove it from the
Database, it will still render. Remove 
the DEM.
18. When asked if you want to
remove the DEM from the disk, answer No; we might want
the DEM later on. Save the project.
18. Render another preview. Aside
from going much faster, you'll see from the Status window
that we're only rendering some of our 70 DEMs. The smaller tiles
free up valuable memory for other operations, which we'll need
later on.
20. Let's group the 10-meter
DEMs on a layer for easy selection. Select the first DEM and
shift-click the last one to select all the DEMs. The titlebar
will show 70 of 74 objects selected.
21. Go to the Layer page
and Show Properties Panel  .
You'll see TOP, which is the default layer VNS creates
on import.
22. Click Add and enter
DEM 10m into the Input Request
window for the Layer Name. This will add all the 10-meter
DEMs to a layer named DEM 10m.
23. To test it, select any object
in the list and select the DEM 10m layer. Use the Select
button to select all objects on that layer. This may not seem
like much help now, but it will be when you have hundreds of
database objects.
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