Teach Yourself VRML 2 in 21 Days/Teach Yourself VRML 2 in 21 Days.iso/mac/ISO9660/3rdparty/POLYTRAN/dos/PT_DOS.ZIP/DOC_1/IMP_VPRO.1

Text File | 1996-06-13 | 7.8 KB | 161 lines

.so psroff.inc        # Include the macros needed for output to Postscript
.TH Import-VistaPro
.SH NAME
imp_VistaPro \- Vistapro Digital Elevation Model (DEM) geometry import filter
.SH SYNOPSIS
.PP
This man page describes the options specific to the Vistapro DEM geometry
import converter.
.PP
.SH EXAMPLE CONVERSION SYNTAX
.PP
To convert a Vistapro DEM file to 3D Studio using the default parameters listed
in the setup.ini file:
.IP
pt -i vpro -o 3ds filename.dem
.PP
To convert a Vistapro DEM file to VRML and override some of the default options
in setup.ini:
.IP
pt -i vpro -in-vpro-skip-factor = 6 -o vrml filename.dem
.PP
.SH OVERVIEW
.PP
This geometry import converter imports, manipulates and converts
digital elevation model (DEM) data in the Vistapro format.
.PP
.SH FEATURES OF THIS CONVERTER
.PP
Vistapro DEM datasets typically contain 60000 or more quadrilateral polygons, or
1200000 triangles (for a 258x258 resolution sample). This is an enormous
number of polygons for most 3d rendering programs so this DEM converter
incorporates two unique options to overcome this problem:
.IP
1) The converter can skip over samples in the dataset so that only every n-th
sample is used. Rather than importing 258x258 samples, the converter imports
51x51 samples (for a skip factor of 5) which results in only 2601 quadrilateral
polygons.
.IP
2) Rather than store the entire DEM dataset in single object, the DEM converter
breaks up the data into multiple smaller objects with a common parent. This
has shown to be an effective method to speeding up the wireframe redraws of the
DEM data (by a factor of 2 or 3), and makes interactive user movement of a 3d
camera much faster since each sub-object is only a few hundred polygons.
In addition, certain rendering programs
(such as Okino's NuGraf renderer) use much less memory when many smaller
objects are used rather than one large object with many polygons. By
default each sub-object stores a maximum of 900 polygons; contrast this with
other converters which lump all 120,000 polygons into a single object - few
renderers will be able to render such a large object.
.IP
3) A default 3d camera is added to the scene which views the DEM data from a
pleasing angle.
.IP
4) u/v texture coordinates are added to the imported data so that a bitmap image
can be easily draped over the DEM data.
.IP
5) The converter creates smoothed vertex normals for the DEM data so that
it will appear to be smooth when rendered.
.PP
.SH COMMAND LINE OPTIONS
.PP
The following options are specific to this import converter:
.TP
-i vpro
This is the optional command line option which specifies that the input data
is in the Vistapro DEM file format. If not specified then the converter will try
to guess the input file's format from its file extension (.dem) and then from the
contents of its file.
.TP
-in-vpro-print-statistics = [ yes | no ]
If set to 'yes' then the converter will print out the number of objects
and polygons created.
.TP
-in-vpro-add-default-camera = [ yes | no ]
If set to 'yes' then the converter will add a default camera to the scene
which views the DEM data at a pleasing angle.
.TP
-in-vpro-skip-factor = #
This switch determines the quality of the imported DEM data (it
directly controls how many polygons will be used to approximate the
input DEM data). THIS IS AN IMPORTANT CONTROL PARAMETER!! A value of
1 results in the highest quality mesh while higher values (2, 3, 4, etc)
result in lower quality, but at the benefit of reducing the number of
polygons in the input data. This number will cause the converter to
'skip' over every n-th input sample. For example, if the input dataset
size is 258x258 samples, and the skip factor is set to 4, then the
converter will actually read in the data as if it were of size 65x65
(258/4 = 65). This will produce 4225 polygons (65x65) instead of
66565 polygons. A value of 2 or 3 (16641 polygons to 7396 polygons)
will produce good results for a final rendering, while values of 5 to 8
will produce small datasets ideal for fast previews (2704 polygons to
1024 polygons).
.TP
-in-vpro-sub-grid-size = #
By default the DEM data will be cut up into several smaller sub-objects
rather than having all of the DEM data clumped together into one huge
object. This option controls how many polygons will be put into each
sub-object. The default is 30 which will cause 900 polygons (30x30)
to be stored in each sub-object. The valid range is 5 to 100.
.TP
-in-vpro-height-scaling-factor = #
This option scales the height of the DEM data. It default to 1.0. Values
greater than 1.0 will make the DEM data higher while values between 0.0
and 1.0 will make the DEM data shorter.
.TP
-in-vpro-add-2d-txtr-coords = [ yes | no ]
If set to 'yes' then u/v texture coordinates will be added to the
imported dataset. These texture coordinates will allow a 2d bitmap image
to be easily mapped to the surface of the data. Please note that the
texture coordinates are aligned with the mathematical bounding quadrilateral
of the dataset, not the actual physical edges of the data (this is because
the physical edges of the data are not square or precise).
.TP
-in-vpro-add-default-2d-texture     = [ yes | no ]
If set to 'yes' then a default 2d bitmap texture file ("default.tif") will
be linked to the DEM data. This option is useful if you intend to apply a
2d bitmap image to the DEM data. The "-in-vpro-add-2d-txtr-coords" option must
also be enabled.
.TP
-in-vpro-texture-2d-u-repeat = 5
.TP
-in-vpro-texture-2d-v-repeat = 5
These two values determine how many times the 2d bitmap texture is to repeat
across the DEM data surface (see the "-in-vpro-add-default-2d-texture"
option above). The default values are 5 which will make the texture repeat
5 times in the horizontal and vertical directions.
.TP
-in-vpro-add-default-3d-texture = [ yes | no ]
If set to 'yes' then a NuGraf "mountain" procedural texture definition
will be added to the scene and assigned to the current shader (useful for
rendering the DEM data with the NuGraf renderer). This texture varies the
color of the DEM data according to the elevation and slope of a polygon (the
color varies from greens, to browns to whites at the highest altitudes).
Please note that this texture tends to be slow to compute due to the turbulence
math functions; a better alternative would be to assign a 2d bitmap texture.
.TP
-in-vpro-create-one-object = [ yes | no ]
If set to 'yes' then one single object is created for all of the imported
data rather than having the data broken up into multiple smaller
sub-objects (the default). The converter automatically sets this to 'yes'
(internally) if the selected output format is to be 3D Studio (this is
because 3D Studio requires all polygons to be inside a single object so
that its smoothing algorithm will work properly; if multiple objects are used
then the vertex normals will not be the same where the sub-objects meet
and hence "cracks" may appear at the junctions).
.TP
-in-vpro-triangulate-data = [ yes | no ]
If set to 'yes' then the DEM data will be imported as triangles instead of
4 sided polygons. This is sometimes useful to enable since 4-sided DEM data
polygons are not planar.
.PP
.SH LIMITATIONS
.PP
If exporting to 3D Studio then all of the DEM data must be exported as one
object so that proper smoothing occurs between the sub-chunks. 3D Studio
has a limit of 64k vertices and 64k polygons, therefore the chunk size must
be set appropriately to limit the number of polygons and vertices output
(the number of polygons created can be verified by setting the
'-in-vpro-print-statistics' option to 'yes' and checking that the number of
polygons created is less than 65536).