RSS Database Specification-1

1.0 Introduction

The Radar Support System (RSS) is a software tool developed for the
Federal Aviation Administration (FAA) that allows the performance of a
radar at a given location to be analyzed. The RSS requires several
databases in order to perform this analysis. This document describes
these databases and their specifications.

The databases are normally collected from stereo photography using
photogrammetric methods. The specifications given assume that this
method is used. For other methods, these specifications may need to be
modified to ensure a database of equivalent quality.

2.0 Databases

The RSS requires a terrain database, a cultural database, and a road
database. All databases are to be supplied in Universal Transverse
Mercator (UTM) coordinates in meters. Horizontal Datum is to be North
American Datum 1983 (NAD-83) and vertical information is to be supplied
relative to the NAD-83 ellipsoid, not the geoid.

Databases are to be supplied on appropriate media (normally CDROM of
DVD) in UNIX tar format or as Unix files on CDROM. Methods of electronic
transfer (e-mail, ftp) could also be employed if agreeable to all
parties involved.

2.1 Terrain Database

The terrain database is to be given as the heights at a regularly spaced
grid of points. These heights are to be given as the actual heights at
the postings, not as an integrated or averaged height about the posting.
The database is to be at 10 meter postings. The postings for the terrain
database are to be at multiples of 10 meters in X (Eastings) and Y
(Northings) relative to the origin in the UTM grid. That is, if the
coordinate is divided by 10, the quotient should be an integer.

The terrain database is to cover the entire stereo imagery. This is
normally a square approximately 20 miles on a side, but can vary. The
terrain database does not need to be either regularly shaped or consist
of a single connected area as long as it covers the specified stereo
imagery. It must, however, include all areas covered by any point in the
cultural database.

A posting for the terrain database is normally to be the ground height,
but in areas where there are trees but no buildings, postings should
follow the canopy, not the ground. The postings for the terrain database
should always be at ground height in areas where buildings are present,
never at the height of the buildings or the trees.

2.1.1 Terrain Database Accuracy

The accuracy required of the terrain databases postings depends on
several factors. The most critical are the scale of the photography used
to collect the database and the resolution at which the photography was
scanned. Another factor is whether the database is being collected at
the tree canopy or at ground height. In addition, errors from other
sources such as triangulation of the photography and other similar
procedures will increase the overall error. In general, postings at
ground height should have no more than the scanning resolution
multiplied by the scale of the photography added to the overall error
due to these other sources. For example, at a photographic scale of
1:40000 and scanning at 25 microns, postings should be accurate to
within 1 meter plus errors due to other sources. For collection of the
canopy, the accuracy of the postings will be much less than collection
of ground points. The highest accuracy possible should be maintained,
however. Ground control, aerial GPS, triangulation, and other processes
are to be performed with sufficient accuracy so as not to significantly
degrade the overall accuracy of the databases.

2.1.2 Terrain Database Output Format

The format of the output terrain database file is to be equivalent to
the Helava DPW \"ascii\" export type. This output format contains the
following information:

> The coordinates of the lower left (southwest) corner of a rectangle
> bounding the database. This rectangle should be aligned along the UTM
> X and Y coordinate axes.
>
> The grid intervals in both the X and Y directions. This should be 10
> meters.
>
> The number of grid points along both the X and Y axes of the bounding
> rectangle. The total number of points in the bounding rectangle
> (product of above) should also be included.
>
> Each valid data point in the database given as the X coordinate, the Y
> coordinate and the Z coordinate (height). Only valid data points
> should be given. Points within the bounding rectangle but outside the
> collected database should not be listed.

The information is to be given to 2 decimal places (centimeter
resolution).

Only one file is to be supplied for all the 10 meter data.

An example file is shown in Table 2.1.

**Table 2.1 Example Terrain Database File**

\#

\# The DTM grid had lower left (southwest) corner coords:

\# X or easting = 580650.00 meters

\# Y or northing = 4717590.00 meters

\# and grid intervals:

\# X (east) grid interval = 10.00 meters

\# Y (north) grid interval = 10.00 meters

\# For a total of 1147 x 1159 = 1329373 points.

\#

\# There may be less points in this file because those

\# grid points that were outside of the polygon that

\# defined the DTM boundary are not included in this file.

\#

590750.00 4717710.00 35.77

590760.00 4717710.00 36.04

591050.00 4717710.00 36.62

.

.

.

2.2 Cultural Database

The cultural database consists of a single file that contains several
different types of features. The various types are listed in Table 2.2
and described in the following paragraphs.

2.2.1 Area of Collection

Features are to be collected in the entire area covered by the stereo
imagery, unless otherwise agreed upon. All features corresponding to the
types listed in the table are to be collected as described in the
following paragraphs.

**Table 2.2 Cultural Database Feature Types**

**[Type Number Form]{.underline}**

SINGLE_BUILDING 10 polyhedron

METAL_BUILDING 11 polyhedron

GLASS_METAL_BUILDING 12 polyhedron

MASONRY_BUILDING 13 polyhedron

WOOD_BUILDING 14 polyhedron

METAL_CIRCULAR_BUILDING 16 polygon

NON_METAL_CIRCULAR_BUILDING 17 polygon

BUILDING_UNDER_CONSTRUCTION 20 polyhedron

MOVABLE_OBJECT 21 polyhedron

ROOFLINE 50 polyline

SINGLE_FAMILY_ROOFLINE 51 polyline

TAXIWAY_SIGN 52 polyline

TOWER 60 point

WATER_TOWER 61 point

RADIO_TOWER 62 point

SMOKESTACK 63 point

FIRE_TOWER 64 point

POWER_LINE_TOWER 65 point

BRIDGE_TOWER 66 point

RUNWAY_LIGHT 67 point

FENCE 70 polyline

WOODEN_FENCE 71 polyline

METAL_FENCE 72 polyline

BLAST_FENCE 73 polyline

RADAR 80 point

SATELLITE_TRACKING_ANTENNA 81 polyhedron

WINDMILL 90 polyline

WINDMILL_TOWER 91 point

WINDMILL_GROUP 92 polygon

BRIDGE 140 polyline

SUSPENSION_BRIDGE 141 polyline

GIRDER_BRIDGE 142 polyline

PIER_TYPE_BRIDGE 143 polyline

ARCH 144 polyline

AIRPORT_SURFACE 150 polygon

RUNWAY 151 polygon

TAXIWAY 152 polygon

APRON 153 polygon

OPEN_TANK 220 polygon

OVERRUN_AREA 154 polygon

MOVEMENT_BORDER 155 polygon

HOLD_LINE 156 polyline

GRASS_LANDING_STRIP 157 polygon

TAXIWAY_CENTER_LINE 158 polyline

RUNWAY_CENTER_LINE 159 polyline

PAVED_SURFACE 200 polygon

AIRPORT_VEHICLE_PATHWAY 204 polygon

TREES 210 polyhedron

OPEN_TANK 220 polygon

2.2.2 Single Features

Single features are collected as polyhedrons, polygons, polylines, or
point features depending on the object type. The table specifies which
form of collection is to be performed for each object type. Polygons are
closed multi-sided two dimensional features. They lie on the ground or
designate the outline of a group of objects. Polyhedrons are polygons
with the addition of dropped sides. Most buildings are in this group.
Polylines are unclosed multi-sided features. Alternatively, they can be
described as a set of connected line segments with the endpoints not
only at different horizontal locations but also possibly different
heights. Point features consist of a single point in three dimensions.

2.2.2.1 Polyhedron and Polygon Feature Forms

Individual buildings are to be collected as polyhedron features. Airport
surface features are to be collected as polygons.

2.2.2.1.1 Single Building Features

Objects of the type SINGLE_BUILDING, METAL_BUILDING,
GLASS_METAL_BUILDING, MASONRY_BUILDING, and WOOD_BUILDING are to be
collected as a connected series of polygons (i.e. a polyhedron). The
roof and each wall of the building are to be collected as individual
polygons. These polygons are to abut at the appropriate corners or
roofline. Peaked or gabled roofs are to be collected as abutting
polygons. Walls are to intersect the ground. Walls that are perfectly
vertical (i.e. normal walls) do not have to be collected. The RSS
software will automatically create walls between the roof and the
ground. All polygons that form an individual building are to be
designated as corresponding to that building by assigning each polygon
the same building number. A building with a complex shaped can be
collected as a series of individual buildings. For this case, walls and
roofs of one building can pass partly or totally through another
building (See Figure 1). It is not desirable to specify in any way that
these individual buildings correspond to a larger building.

![](media/image1.png){width="3.4402777777777778in"
height="3.053472222222222in"}

Figure 1 Overlapping Features

If the construction material of the building can be determined with
certainty, it should be specified by choosing the appropriate feature
type. Only four materials can be chosen, METAL, GLASS_METAL, MASONRY and
WOOD. If the material type cannot be determined with certainty, the
feature type should be set to SINGLE_BUILDING.

Buildings that are cylindrical (storage tanks, etc.) should be
approximated as an even number of flat surfaces around the circular
surface. The number of flat surfaces used should not be less than 20.
The vertices separating these flat surfaces should be equally spaced
around the cylinder and should fall on the cylinder. Alternatively,
three points can be collected around the outside of the cylindrical
building and the RSS software will create the circular roof and walls.
The feature type must be METAL_CIRCULAR_BUILDING or
NON_METAL_CIRCULAR_BUILDING in order for the RSS software to process the
three points into a cylindrical building. The three points do not have
to be equally spaced around the building, but greater accuracy will
result with more equal spacing.

Cylindrical tanks that are open on the top (sewage treatment is common)
are to have both the outside and inside of the tank wall collected. The
roof in this case is the top of the wall. An alternative method of
collection exists for this type of structure, also. Five points need to
be collected: three point around the outside of the tank at the height
of the wall, an additional point on the inside of the wall, and a point
anywhere on the inside of the tank, at the level of the inside surface.
The RSS software will create a circular building with the proper width
and a water surface inside the created building. The feature type must
be OPEN_TANK.

The points that must be collected for cylindrical objects are
illustrated in Figure 2.

Figure 2 Collection of Cylindrical Buildings

Buildings that have a courtyard or other non-building interior cannot be
collected as one object located inside another. Examples of these types
of buildings are the open tank just discussed and an open air sports
stadium. These buildings must be collected as two abutting buildings,
each roughly in the shape of the letter C, This is shown in Figure 3,
where individual features are shown in different colors.

Figure 3 Incorrect and Correct Method of Collecting Courtyard Building

Any building that is in the process of being built (outside dimensions
are changing) should be collected as a feature of type
BUILDING_UNDER_CONSTRUCTION. The specifications for collecting this
building are the same as for a Single Building feature type.

2.2.2.1.1.1 Building Size

Buildings that are larger than a single family house are to be collected
as single buildings. Also a building at least the size of a house is to
be collected as a single building if it is within 3000 feet of any
airport surface at the specified primary airport(s).

2.2.2.1.2 Airport Surface Features

Airport Surfaces consist of the feature types AIRPORT_SURFACE, RUNWAY,
TAXIWAY, APRON, OVERRUN_AREA, MOVEMENT_BORDER, and GRASS_LANDING_STRIP.
All surfaces that aircraft can travel on are to be collected. RUNWAYs,
TAXIWAYs and APRONs are self explanatory. The OVERRUN_AREA is the area
at the end of a runway, also called the blast pad. The MOVEMENT_BORDER
is that area bordering TAXIWAYs, RUNWAYs, etc. that is paved but
aircraft are not permitted on. This is often called the shoulder.
General airport surfaces that aircraft can travel on can be collected as
objects of type AIRPORT_SURFACE. Areas that are no longer used as
aircraft movement areas are to be collected as PAVED_SURFACE features.
In addition all marked centerlines are to be collected as
TAXIWAY_CENTER_LINE or RUNWAY_CENTER_LINE polyline features.

Any of the airport surfaces can be collected as a series of smaller
polygons, rather than a single large polygon. For example, a single
runway can be collected as multiple polygons of type RUNWAY. All airport
surface polygons, however, must perfectly abut adjacent polygons
horizontally and vertically, whether of the same object type or not.
Overlaps and gaps are not permitted. This is illustrated in Figure 4.
Each individual polygon is to have a unique building number, even if
part of a larger feature. A sufficient number of vertices in the
polygons are to be collected in order to follow the elevation contour of
the surface.

![](media/image2.png){width="3.097916666666667in"
height="2.7555555555555555in"}

Figure 4 Poor Abutment Between Shoulder and Taxiway

Only the \"tops\" of airport surfaces are to be collected. Runways,
taxiways, etc. have no sides (i.e. they are polygons, not polyhedrons).

As with courtyard type buildings, a grassy area entirely enclosed by
paved airport surfaces must not be collected as two concentric airport
surface features. Instead, airport surfaces in the shape of abutting C
shaped objects must be used. Correct collection is shown in Figure 5,
where the triangular shape near the center is a grassy plot, the grey
areas next to it are paved shoulders (MOVEMENT_BORDER) and the area
outside that are taxiways. The taxiways are colored red, but are
occasionally overwritten in the display by the shoulders. Notice that
the shoulder encircling the grassy area is sectioned into abutting
parts. Similarly, the taxiways encircling the shoulders are also
sectioned into parts.

![](media/image3.png){width="2.0625in"
height="1.8305555555555555in"}![](media/image4.png){width="2.0625in"
height="1.825in"}![](media/image5.png){width="2.0625in"
height="1.825in"}

Figure 5 Correct Collection of Grassy Areas Surrounded by Shoulders
Surrounded by Taxiways

2.2.2.2 Polyline Feature Forms

Fences, bridges and certain rooflines are to be collected as polyline
features. In addition, airport centerlines and hold lines are to be
collected as polyline features.

2.2.2.2.1 Fences

Fences consist of the feature types FENCE, WOODEN_FENCE, METAL_FENCE,
and BLAST_FENCE. These feature types are to be collected as a series of
line vertices along the top of the fence. A single fence can be
collected either as a single polyline or as a series of shorter
polylines. If the fence is collected as a series of polylines, each
polyline in the series must be started at the exact position of the
ending vertex of the previous polyline. The building number of each
polyline should be unique, even if it is part of a longer fence. If the
type of fence can be determined, it should be specified by choosing the
appropriate feature type. Only WOODEN_FENCE, METAL_FENCE, and
BLAST_FENCE can be chosen. WOODEN_FENCE and METAL_FENCE specify the
material the fence is constructed from. BLAST_FENCE is the (usually
concrete) fence set up at the end of a runway to protect from aircraft
engine blast. If the fence type cannot be determined, FENCE should be
chosen for the object type.

If a fence is wide enough so that a line can be drawn along each side,
then the fence should be collected as a single building type object
rather than a fence type object. Only those fences that are so thin they
can only be collected as a single line should be collected as an object
type of FENCE, WOODEN_FENCE, METAL_FENCE, or BLAST_FENCE.

2.2.2.2.2 Bridges

Bridges consist of the feature types BRIDGE, SUSPENSION_BRIDGE,
GIRDER_BRIDGE and PIER_TYPE_BRIDGE. These feature types are to be
collected as a series of line vertices at the level of the roadway or
walkway of the bridge. A bridge should be collected as a single polyline
object. The type of bridge should be specified by choosing the
appropriate feature type. A SUSPENSION_BRIDGE is self explanatory. A
GIRDER_BRIDGE has a network of steel girders bolted or welded together
and extending either below or above the roadway. A PIER_TYPE_BRIDGE has
concrete posts below the roadway. This is commonly used for Interstate
highway overpasses, and is also used for long bridges over relatively
shallow water. If the bridge type cannot be determined or does not fall
into one of the specified categories, then the generic BRIDGE feature
type should be specified.

2.2.2.2.3 Rooflines

Buildings that are the size of single family houses are to be collected
as ROOFLINE or SINGLE_FAMILY_ROOFLINE type features. A single line is to
be drawn along the peak of the roofline of these buildings. Single
family houses are to be collected as a feature type of
SINGLE_FAMILY_ROOFLINE. Other buildings of the same size are to be
collected as ROOFLINE. A building is not to be collected as a ROOFLINE
or SINGLE_FAMILY_ROOFLINE type feature within 3000 feet of any airport
surface feature. These buildings, regardless of size, are always to be
collected as single buildings. Also, single family sized houses that are
part of a closely spaced development (and greater than 3000 feet from an
airport surface) are not to be collected.

2.2.2.3 Point Feature Forms

Tall features that are too narrow in diameter to collect as single
buildings are to be collected as point features. Point features consist
of the types TOWER, WATER_TOWER, RADIO_TOWER, SMOKESTACK, FIRE_TOWER,
POWER_LINE_TOWER, and BRIDGE_TOWER. These features are to be collected
as a single point at the height of the top of the object. Objects that
have a sufficient diameter that the outside can be traced are to be
collected as a single building type feature, not as a point type. If the
use of the tower can be determined, it is to be collected as the
corresponding feature type. A POWER_LINE_TOWER is the tower used to hold
high tension power lines, not the normal street \"telephone pole\",
which does not normally have to be collected. A BRIDGE_TOWER is the
concrete or steel tower that holds up a suspension bridge. For towers
that cannot be determined to be in one of the specified categories, the
generic feature type TOWER is to be used. Any tower that rises above the
height of its surroundings is normally to be collected. Street lights
usually do not have to be collected, unless they are of the type that
are extremely high towers (often used in large parking lots).

2.2.3 Windmills

Windmills used for electrical generation are to be collected in a unique
manner. Windmills used to pump water do not need to be collected in this
manner. A TOWER point feature or a SINGLE_BUILDING polyhedral type is
sufficient for windmill water pumps.

A single windmill is to be collected as a WINDMILL polyline feature
containing exactly three points. The first point is to be at the X and Y
location of the farthest extent of a blade. The second point is to be at
the X, Y, and Z location of the blade hub. The third point is to be at
the X and Y location of the farthest extend of a blade on the opposite
side from point one. This is illustrated in Figure 6. Only point 2
requires an accurate height value.

![](media/image6.png){width="3.4402777777777778in"
height="3.053472222222222in"}

Figure 6 Windmill Collection

Windmills are often placed in "farms" of hundreds or thousands. To ease
collection, a single windmill can be collected using the above method.
All other nearby windmills of the exact same type can be collected as
WINDMILL_TOWER types. A single bounding polygon of type WINDMILL_GROUP
is then placed around the fully collected WINDMILL feature and the
WINDMILL_TOWER features. The polygon can contain only one WINDMILL
polyline feature and all WINDMILL_TOWER point features must correspond
to windmills with the exact same dimensions as the WINDMILL polyline
feature. This process can be repeated for windmills with different
dimensions as long as the WINDMILL_GROUP polygons do not overlap.

The RSS software calculates blade length and tower height from the
WINDMILL polyline feature and applies these dimensions to all
WINDMILL_TOWER features located within the WINDMILL_GROUP containing the
WINDMILL polyline.

2.2.4 Cultural Database Output Format

The cultural database is to be provided in the Helava DPW \"ascii\"
export type format. An example of this format is given in Table 2.3.

Table 2.3 Cultural Database Output Format Example

2 SINGLE_BUILDING 10 5 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

600032.421875 4751122.011719 0 44.799999

600065.220703 4751110.632812 0 44.799999

600061.224609 4751099.117188 0 44.799999

600028.427734 4751110.500000 0 44.799999

600032.421875 4751122.011719 0 44.799999

2 SINGLE_BUILDING 10 5 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

600065.220703 4751110.632812 0 44.799999

600032.421875 4751122.011719 0 44.799999

600032.421875 4751122.011719 0 37.784172

600065.220703 4751110.632812 0 38.427219

600065.220703 4751110.632812 0 44.799999

2 SINGLE_BUILDING 10 5 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

600061.224609 4751099.117188 0 44.799999

600065.220703 4751110.632812 0 44.799999

600065.220703 4751110.632812 0 38.427219

600061.224609 4751099.117188 0 39.170845

600061.224609 4751099.117188 0 44.799999

2 SINGLE_BUILDING 10 5 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

600028.427734 4751110.500000 0 44.799999

600061.224609 4751099.117188 0 44.799999

600061.224609 4751099.117188 0 39.170845

600028.427734 4751110.500000 0 37.861046

600028.427734 4751110.500000 0 44.799999

2 SINGLE_BUILDING 10 5 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

600032.421875 4751122.011719 0 44.799999

600028.427734 4751110.500000 0 44.799999

600028.427734 4751110.500000 0 37.861046

600032.421875 4751122.011719 0 37.784172

600032.421875 4751122.011719 0 44.799999

2711 POWER_LINE_TOWER 65 1 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

default.icn

5 0 0 0.000000

600489.337891 4738388.925781 0 42.299992

8968 FENCE 70 3 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

603046.722656 4723548.348145 0 1.299997

603058.962891 4723542.367676 0 1.299997

603052.792969 4723553.450195 0 1.299997

28263 SINGLE_FAMILY_ROOFLINE 51 2 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

613920.035156 4725073.716309 0 129.800003

613902.648438 4725074.390625 0 129.800003

5622 TAXIWAY 152 5 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

598441.503906 4733565.715820 0 54.500000

598108.882812 4733550.741211 0 52.799999

598108.570312 4733574.018555 0 52.799999

598441.177734 4733590.004883 0 54.200001

598441.503906 4733565.715820 0 54.500000

5623 TAXIWAY 152 11 NO_LAYER

ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES

598108.570312 4733574.018555 0 52.799999

598072.968750 4733572.378906 0 52.000000

598070.826172 4733580.439453 0 52.000000

598075.777344 4733590.649414 0 52.599998

598058.275391 4733605.525391 0 52.599998

598028.169922 4733573.613281 0 51.799999

598011.929688 4733570.290039 0 51.599998

597909.208984 4733564.430664 0 51.500000

597908.505859 4733541.135742 0 51.299999

598108.882812 4733550.741211 0 52.799999

598108.570312 4733574.018555 0 52.799999

A feature of type SINGLE_BUILDING is listed first. The order the feature
types are listed is unimportant. A feature of type SINGLE_BUILDING, the
second entry in line 1, is a feature of type number 10, the third entry
in line 1. The corresponding feature number for each feature type can be
found from Table 1. The roof of the building is listed first. It has 5
vertices (the fourth entry in line 1), with the first and last equal,
giving a closed polygon. This building is designated as feature number
2, the first entry in line 1. Notice that the next four polygons also
are designated as feature 2. These next four polygons are the walls of
the SINGLE_BUILDING. Line 1 ends with NO_LAYER, and line 2 is
ELEMENT_ATTRIBUTES END_OF_ELEMENT_ATTRIBUTES. The coordinates of each
vertex follow on separate lines, with x,y and z as the first, second,
and fourth entries of each line. An integer 0 is the third entry of each
line. The x,y and z coordinates are real values to at least millimeter
resolution (three decimal places).

The next feature is a POWER_LINE_TOWER (second entry on line) of feature
type number 65 (third entry). This is the 2711th (first entry on line)
feature in the list. (This is a very abbreviated sample of an actual
feature file containing almost 30,000 features.) The number of vertices
for a point feature is set to 1 (fourth entry on line). The line ends
with NO_LAYER, and the second line of the entry is ELEMENT_ATTRIBUTES
END_OF_ELEMENT_ATTRIBUTES. The third line is default.icn and the fourth
line is 5 0 0 0.000000. The fifth line contains the x (first entry), y
(second entry) and z (fourth entry) coordinates of the point. An integer
0 is the third entry of this line.

The next feature is a FENCE of feature type number 8968. This has 3
vertices. The first vertex is unequal to the last, as should be the case
for a polyline, which is unclosed. There is only one entry associated
with this feature (number 8968), unlike the SINGLE_BUILDING, which had
five entries corresponding to the roof and four walls.

Feature number 28263 is a SINGLE_FAMILY_ROOFLINE, an object of type
number 51. This feature has two vertices.

The next two features, numbers 5622 and 5623, are of type TAXIWAY and of
type number 152. The first taxiway is a polygon with 5 vertices, the
first vertex equaling the last vertex. The second taxiway is a polygon
of 11 vertices. As with all polygons, the first vertex equals the last
vertex. Notice that vertices 10 and 11 (and 1) of the second taxiway
equal, in x ,y and z, vertices 2 and 3 of the first taxiway. This means
that the second taxiway perfectly abuts the first taxiway, as required.

2.2.5 Cultural Database Accuracy

The accuracy required of the vertices for a single feature in the
cultural database is the same as for the ground points in the 10m
terrain database. Vertices should have no more than the scanning
resolution multiplied by the scale of the photography added to the
overall error due to other sources. At a photographic scale of 1:40000
and scanning at 25 microns, vertices should be accurate to within 1
meter plus errors due to other sources.

2.2.6 Cultural Database Feature Squaring

Buildings that have corners that form right angles are to be collected
so that the segments connecting vertices also form right angles. These
angles formed by the segments are to be within 0.1 degrees of 90 degrees
at all corners that correspond to a right angle of the building.

2.3 Road Database

The road database consists of a series of polylines corresponding to the
roads and railroads within a 60 nautical mile radius of the center of
the stereo imagery or other point specified. It is expected that the
polylines are to be a corrected form of the USGS or other public road
database and in a different format. Also, the polylines are to have a z
coordinate corresponding to the height of the road.

Within the area covered by stereo imagery, the USGS database is to be
corrected so that the polylines fall along the center of the
corresponding roads or railroads. Polylines in the database that do not
correspond to roads in the imagery are to be removed. Polylines are to
be added to the database to correspond to any uncollected roads in the
imagery. Ideally, all polylines are to fall exactly at the center of the
corresponding road. Under no circumstances are the polylines to pass
through any building feature, unless the corresponding road also does
(tunnel under a building, etc.). The height of the road is to be
accurate to within 2 meters.

Outside the area covered by stereo imagery, it is not possible to
determine whether the polylines actually are aligned with the roads.
However, there is to be no discontinuity in the database within the area
covered by the imagery and that outside. The polylines in the area
outside the imagery are to be adjusted so that they align with the
polylines within the area of imagery. There are to be no twists or
additional bends added to the database that do not correspond to the
actual road.

2.3.1 Road Database Output Format

The road database is to be provided in the Helava DPW \"ascii\" export
type format. This is the same format as the cultural database format
described in Sections 2.2.1 and 2.2.4, but with different feature types.

There are five output feature types for the road database. USGS lines
with a major attribute code of 170 and minor attribute codes of 0201,
0202, 0203, and 0204 are to be output as a feature type of
PRIMARY_HIGHWAY (feature type number 111). USGS lines with a major
attribute code of 170 and minor attribute codes of 0205, 0206, 0207, and
0208 are to be output as a feature type of SECONDARY_ROAD (feature type
number 112). USGS lines with a major attribute code of 170 and minor
attribute codes of 0209, 217, 218 and 221 are to be output as a feature
type of STREET (feature type number 113). USGS lines with a major
attribute code of 170 and a minor attribute code of 0210 is to be output
as a feature type of CLASS_4_STREET feature type number 114). USGS lines
with a major attribute code of 180 and minor attribute codes of 0201,
0202, 0203, and 0204 are to be output as a feature type of RAILROAD
(feature type number 130).

For a road database that is produced from non-USGS sources, a reasonable
correspondence is to be made between the above five feature types and
the road types in the source files.