Vr Mapping

ON-LINE REFERENCE DOCUMENTATION

CARDINAL SYSTEMS, LLC

www.cardinalsystems.net

Point Display (PoiDis or PO)

PointDisplay

LiDAR

 

Type: Display Management

 

Allows user to manage the parameters that control the display of Points.

 

Detailed Description

Point Display Dialog

 

Point Display Filters

Z Slice

Classification

List Classifications Used

Return Number

Sensor Number

Flight/strip Number

GPS Time

Scan Angle

Key-point

Adjust Clip Limits on Recenter

Reset Filters on Startup

 

Point Color Parameters

Entity

Intensity

Intensity Histogram

Classification

RGB

Elevation

Elevation Histogram

Slice

Sensor Number

Flight/strip Number

 

Point Display Key-ins

 

Detailed Description

Several point display criteria may be controlled.  Points may be filtered based on Z Slice, classification, return number, sensor number, flight/strip number, GPS time, scan angle and/or keypoint.  Any or all of these filters may be selected.  When displaying Points in 3D ViewPoint and 2.5D ViewPoint, near and far clip limits may be applied to help isolate points within a viewing slice based on the 3D eye point position and direction.

 

Points may be colored based on layer (entity), LiDAR intensity, classification, RGB color values, point elevations or Z slice, sensor number, or flight/strip number.  Many of the color display modes include additional parameter settings.  Any of the coloring options such as elevation may be supplemented by draping the Intensity values which offers a dual coloring method in most configurations.

 

Several reporting applications are available including a LiDAR intensity histogram and the LiDAR classification use.

 

Other key-in commands that further control Point display include the Point Density (PD) command which allows the skipping of points during display and Point Size (PS) command which controls the size of the Points during display .  The parameters defined in Point Display (PoiDis) are used when displaying Points in the VrOne 2D window, VrTwo stereo with images or LiDARgrammetry images and in 3D ViewPoint.

Point Display Dialog

PointDisplayMainDialog

Point Display main dialog box

 

The Point Display dialog box is divided into the Point Display Filters area and the Point Color Parameters.

The Point Display Filters display points based on one or more criteria.
The Point Color Parameters define the coloring scheme when points are displayed.  One of the six color options may be active at a time.

Point Display Filters

Multiple point display filters may be checked.  For example, it would be possible to display only points that are classified as vegetation a last return number in the elevation range of 100 to 120 ground units.

 

Pressing the Edit button to the right of the checkbox will allow the definition of parameters for that point display filter.

 

Point Display Filters - Z Slice

Displays a slice of Point data that is defined as an elevation range.  This filter is useful when some of the point data obscures other data such as decks, tunnels and areas of tree cover.  The Z Slice filter may be turned on/off with the check box.  The following is an example of a Z Slice applied to an overpass area in which LiDAR data was collected both on a highway overpass and on the roadway under the overpass.  By using the Z Slice filter, either the overpass or the roadway may be isolated for viewing and data collection.

Points with an elevation in the Z Slice range will be displayed if the point passes other active point filters also.

 

The interactive application Point Set Z (PoiSetZ) is also available which allows the definition of the Z Slice parameters with the option to digitize the base elevation.

 

PointDisplayZSlice01

Overpass area with all data displayed

 

PointDisplayZSlice02

Overpass area with Z Slice showing roadway without bridge deck

 

PointDisplayZSlice03

Overpass area with Z Slice showing bridge deck without road

 

PointDisplayZSliceDialog

The Z Slice parameter dialog

Z Slice Base Z

Defines the elevation base for the Z Slice in ground units.

Z Slice Minimum Delta Z

Defines the lower range of the Z slice using a delta Z from the base Z.  This value is typically a negative number.  The example in the above dialog would set the Z Slice range from 123 to 130.

Z Slice Maximum Delta Z

Defines the upper range of the Z slice using a delta Z from the base Z.  This value is typically a positive number.  The example in the above dialog would set the Z Slice range from 123 to 130.

 

Point Display Filter - Classification

Defines up to 32 LiDAR Classifications to be displayed.  Points with these classifications will be displayed if the point passes other active point filters also.  The "Check all" button selects all classifications and the "Uncheck all" de-selects all classifications.

 

PointDisplayClassDialog

The Point Display Filter for Classifications

 

List Classifications Used - Point Color Parameters

Pressing the "List classifications used" button will display the LiDAR Classifications that are used in the currently opened VrOne files.

 

PointDisplayClassUsed

Results of "List classifications used"

 

Point Display Filter - Return Number

The LiDAR Return Number is the pulse return number for a given output pulse. A given output laser pulse can have many returns. They are marked in sequence of return. A single output pulse may have up to five returns.  The Return Number filter defines and displays only the points that match the specified return number.

 

Points with the user specified return number will be displayed if the point passes other active point filters also.

 

Pressing the Edit button will display the following dialog and allow the definition of the return number to display.

 

PointDisplayReturnNumber

The Return Number dialog

 

The Return Number may be from one to five or the last return.  Typically the Points with the last return are the lowest points and considered to be on the ground.  By selecting the last return, many points in vegetation and trees are not displayed.  In the examples below, one scene from 3D ViewPoint displays LiDAR Point data will all the returns. Another shows only the last returns.

 

PointDisplayReturnNumber02

A scene from 3D ViewPoint showing LiDAR Point data will all returns

 

PointDisplayReturnNumber01

A scene from 3D ViewPoint showing LiDAR Point data will the last return only

 

Point Display Filter - Sensor Number

LiDAR collection platforms such as mobile LiDAR may use more than one sensor that work simultaneously.  The Sensor Number parameter allows filtering by up to eight sensor numbers.  On input, the sensor number may be embedded in the input file name.  Starting at LAS version 1.4, the sensor number is a point attribute in this format.  A number line may be entered for this parameter.

 

PointDisplaySensorDialog

Sensor number filter dialog

 

Point Display Filter - Flight/strip number

Each point in the VrPoint (LiDAR) database has an attribute for the storage of the flight or strip number.  In aerial applications, this number may indicate a flight line number; in mobile LiDAR collection, it may indicate a pass number.  On input the flight/strip numbers may be embedded in the input file name.  This attribute is not part of the LAS format. A number line may be entered for this parameter.

 

PointDisplayFlightDialog

Flight/strip number filter dialog.

 

Point Display Filter - GPS Time

If the VrPoints are saved with the available GPS time, points may be filtered based on a minimum and maximum GPS time.  The parameters are typically expressed in seconds from a known start time.

 

PointDisplayGpsDialog

GPS Time filter dialog

 

Point Display Filter - Scan Angle

VrPoints may be filtered by their scan angle attribute.  This may be useful when isolating the points directly under the sensor.  The Scan Angle is entered in degrees.

 

PointDisplayScanAngleDialog

Scan Angle filter dialog

 

Point Display Filter - Keypoint

Keypoints or model Keypoints are used to thin LiDAR datasets by identifying points in flat areas that represent other LiDAR points nearby to be within the same user defined elevation tolerance.  When the keypoint filter is active only VrPoints that are defined as keypoints are displayed.

 

Point Display Filter - Adjust Clip Limits on Recenter

This parameter is used only by the VrThree (VrLiDAR) 3D ViewPoint environment. If checked, it adjusts the near and far clip limits each time the screen is re-centered.  The Edit button allows the definition of the near and far clip and clip increment values.  See Getting Started with 3D ViewPoint for information for turning on/off and changing the near and far clip limits interactively while in 3D ViewPoint.

 

When viewing Point data in 3D ViewPoint, clipping planes are used to prevent the display of data that is "near to" or "far away" from the viewer's eye point or center of projection.  The planes are perpendicular to the camera and set at user definable distances from the 3D center of the current scene.  The near clip place is set in front of the 3D center and the far clip plane is set behind it.  The clipping planes are useful when using ground based LiDAR in situations such as tunnels, roadway overpasses or other data in which data outside the current area of interest obscures or overlays this area.  The clip limits are also useful when using aerial LiDAR to help minimize tree cover.

 

PointDisplayClipDiagram

Near and far clip diagram

 

The following two ground based static LiDAR examples show a 3D scene in which a tree obscures the area of interest then the result of the application of a near clip to remove the tree from the view.  Once the near clip is activated and positioned, the user can move the eye point closer to the area for viewing and data collection and measurements.  The eye point may also be rotated in any direction in X Y and Z and the near and far clips will remain in effect allowing the area of interest to be viewed from any angle and at any scale.

 

PointDisplayClip01

A scene from 3D ViewPoint showing a tree obscuring the area of interest

 

PointDisplayClip02

A scene from 3D ViewPoint showing the result of the application of a near clip

 

The values entered into the Near/Far Clip dialog are in arbitrary units from 1-100.  The near and far clip distances may be edited interactively when clips are on in the 3D Viewpoint environment.  If the "Adjust clip limits on recenter" is checked then the near and far clip distances will be modified when a new 3D center for the view is computed (recentered).

 

PointDisplayClipDialog

The Near/Far Clip dialog

Near Clip Distance (1-100)

Defines the distance from the 3D center of the view to the near clip plane.

Far Clip Distance (1-100)

Defines the distance from the 3D center of the view to the far clip plane.

Clip Display Increment (1-100)

Defines the near and far clip distance increment to add or subtract from the existing near and far clip distances when editing these values interactively.

 

Point Display Filter - Reset Filters on Startup

If this parameter is checked, the Z Slice filter, classification filter, return number filter will be unchecked and the Adjust clip limits on re-center will be checked when VrOne or VrTwo is started.

 

Point Color Parameters

The Point Color Parameters define the coloring scheme when points are displayed. Not all color options are supported by all LiDAR (Point) data sets.  For example, RGB is typically not used for aerial based LiDAR.

Only one point color checkbox may be active.  Pressing the Edit button to the right of the checkbox will allow the definition of parameters for that point color item.

 

Point Color Parameters - Entity

The Entity color option colors VrPoints (LiDAR) by their layer numbers.  This method uses the same method lines, symbols and text use to set colors which is with pen numbers.  VrPoints are colored using the same color parameters that are used to color Vr Symbols using a pen table.

 

Point Color Parameters - Intensity

Each point in the database carries an intensity along with many other LiDAR point attributes.  Intensity is one of the most popular methods used for coloring points.

 

In the measurement of light, intensity means irradiance, which is optical power per unit area (watts per square meter). The imprecise definition would be how much light (watts) the instrument received.  There are a number of factors that affect the intensity value:

 

1.How much light was sent out;
2.Range to the target;
3.Attenuation of beam by atmosphere;
4.Reflectance of target (at the appropriate wavelength);
5.Incident angle of light on the target surface;
6.Size of receiver aperture;
7.Efficiency of receiver optics at focusing the return light onto receiver sensor;
8.Specularity reflection of the target surface.

 

Point Color Parameters - Intensity Histogram

The range of intensity vary between different LiDAR sensors and manufacturers.  The Intensity histogram button displays a dialog containing the intensity range and point counts of the intensity values in the currently opened VrOne files.

 

PointDisplayIntensityHistogram

The Intensity histogram dialog

 

The above intensity histogram shows an intensity range from 0 to 255 however the majority of the point intensities are in the range of 0 to approximately 50.  Moving the cursor over the histogram area of the dialog displays the intensity value and the number of points that have that value.

Point Color Parameters - Intensity Edit

PointDisplayIntensity

The Intensity parameter dialog

 

The Intensity histogram may be used to determine the usable intensity value range of the currently opened VrOne files (see Intensity Histogram).

Intensity Minimum

Defines the minimum intensity value for which the start color will be assigned.

Intensity Maximum

Defines the maximum intensity value for which the end color will be assigned.

Start Color

Defines the start color value.  Press the color square to change the color assignment.  Point colors will be blended from the start color to the end color for point intensities between the minimum and maximum intensities.

End Color

Defines the end color value.  Press the color square to change the color assignment.  Point colors will be blended from the start color to the end color for point intensities between the minimum and maximum intensities.

 

Point Color Parameters - Classification

User-defined colors may be assigned to each of the 32 ASPRS standard LiDAR point classes.

 

Point Color Parameters - Classification Edit

Color values may be assigned by pressing the color squares.  The "Color blend" button will blend color assignments between classification 0 and classification 31.  Classification 0 is the start color and classification 31 is the end color.  The "Color random" button sets color assignments randomly for the 32 classifications.

 

PointDisplayColorClassification

The Intensity color assignment dialog

 

Point Color Parameters - RGB

The point data base contains three color channels for each LiDAR point if these values exist.  These fields are used to color each point and are normally obtained using secondary data, typically a camera.  Checking this options will use these values.  White will be used if RGB is not available.

 

PointDisplayRGB

LiDAR points with RGB assignments

 

Point Color Parameters - Elevation

Colors points by elevation.  Not all LiDAR data contains point intensities, classifications, or RGB values, but the data always contains elevations for each point.  The option to color points using elevations is always available.

 

PointDisplayElevation01

Point colors based on elevation

 

Points that fall below the minimum defined elevation will use the start color and points that fall above the maximum defined elevation will use the end color.

 

PointDisplayElevation

Point Color Parameters - Elevation dialog

Use elevation range

When displaying point colors based on elevation, the elevation range may be defined "From Point data" or "From a user defined Z range".  If  "From user defined Z range" is selected then the minimum and maximum user defined Z will be used.

Minimum user defined Z

If the "Use elevation range" option is set to "From user defined Z range", this value will be used for the minimum elevation when setting point colors.

Maximum user defined Z

If the "Use elevation range" option is set to "From user defined Z range", this value will be used for the maximum elevation when setting point colors.

Elevation increment (0=none)

If this parameter is set to a non zero positive number, the Point colors will be held to a constant value for this elevation increment  (see example below). When this parameter is set to zero, the point colors are evenly blended from the minimum defined elevation to the maximum defined elevation.

Use color scale

Using the color scale defines the color for the lowest elevations to the highest in a predefined, broad color range.  This setting overrides the "Start color" and "End color" parameters.

Use start/end colors (below)

When checked, the "Start color" and "End color" parameters will be used to define the colors for the lowest to highest elevations.

Start color (Lowest Elevations)

Defines the start color value for the lower elevation.  Press the color square to change the color assignment.  Point colors will be blended from the start color to the end color for elevations between the minimum and maximum elevation range.

End color (Highest Elevations)

Defines the end color value for the highest elevation.  Press the color square to change the color assignment.  Point colors will be blended from the start color to the end color  for elevations between the minimum and maximum elevation range.

 

PointDisplayElevation02

Point colors based on elevation using the Elevation Increment option

 

 

PointDisplayElevation03

Point colors based on elevation using start and end colors of red and blue

 

PointDisplayElevation04

Point colors based on elevation using color scale

 

Point Color Parameters - Elevation Histogram

The Elevation histogram button displays the elevation range values of the VrPoints in the currently opened VrOne files.

 

PointDisplayElevation05

Elevation histogram

 

Point Color Parameters - Slice

This option allows the setting of individual colors for user defined elevation ranges.  This option is useful when elevation ranges need to be identified.

 

PointDisplayColorSlice01

Scene from 3D ViewPoint of Mount St. Helens showing color slices

 

PointDisplayColorSlice02

Scene from VrOne of Mount St. Helens showing color slices

 

Up to 20 elevation slices may be defined.  If both the minimum and maximum elevations are set to zero the slice will not be used.

 

PointDisplayColorSliceDialog

Point Color Parameters -Slice Dialog

Minimum User Defined Z

Defines the minimum elevation for the Z slice in ground units.

Maximum User Defined Z

Defines the maximum elevation for the Z slice in ground units.

Color

Shows the current color for the Z slice.  Press the color square to change the color.

 

Point Color Parameters - Sensor Number

LiDAR collection platforms such as mobile LiDAR may use more than one sensor that work simultaneously.  The Sensor Number parameter allows filtering by up to eight sensor numbers.  On input, the sensor number may be embedded in the input file name.  Starting at LAS version 1.4, the sensor number is a point attribute in this format.  Selecting "Sensor number" colors points based on up to eight sensor numbers.

 

Color values may be assigned by pressing the color squares.  The "Color blend" button will blend color assignments between sensor number 0 and sensor number 7.  Sensor color 0 is the start color and sensor color 7 is the end color.  The "Color random" button sets color assignments randomly for the 8 sensors.

 

PointDisplaySensorColorDialog

Point Color Parameters - Sensor color dialog

 

Point Color Parameters - Flight/strip Number

Each point in the VrPoint (LiDAR) database has an attribute for the storage of the flight or strip number.  In aerial applications, this number may indicate a flight line number; in the case of mobile LiDAR collection, it may indicate a pass number.  On input, the flight/strip numbers may be embedded in the input file name.  This attribute is not part of the LAS format. Selecting "Flight/strip number" will color points based on their flight/strip number.

 

Color values may be assigned by pressing the color squares.  The "Color blend" button will blend color assignments between flight/strip number 0 and flight/strip number 255.  Sensor color 0 is the start color and sensor color 255 is the end color.  The "Color random" button sets color assignments randomly for the 256 flight/strip numbers.

 

There are 256 possible flight numbers from 0 to 255.  64 of these flight/strip numbers are displayed in the dialog at one time.  Pressing the Previous or Next buttons will move between the four possible pages.

 

PointDisplayFlightColorDialog

Point Color Parameters - Flight/Strip Number dialog

 

Point Color Parameters - Intensity Drape

When coloring VrPoint (LiDAR) data using any of the coloring options (except Intensity) it is possible to add intensity coloring in addition to the current coloring option.  Selecting "Intensity Drape" will turn this coloring addition on.

 

PointDisplayIntensityDrape01

Point colors based on elevation using color scale without Intensity Drape

 

PointDisplayIntensityDrape02

Point colors based on elevation using color scale with Intensity Drape

 

Point Display Key-ins

Following are equivalent Vr key-ins for conditioning the Point Display parameters.

 

Description

Key-in

Keyword

Parameters

Example

 

 

 

 

 

Point Display Filter - Z Slice - On/Off

PoiFilZsl

On|Off|Tog

 

PoiFilZsl  On

Point Display Filter - Z Slice - Set Base Z

PoiFilZsl

BasZ

BaseZ

PoiFilZsl  BasZ  117.0

Point Display Filter - Z Slice - Set Z Range

PoiFilZsl

RanZ

RangeZ

PoiFilZsl  RanZ  4.0

Point Display Filter - Minimum Delta Z

PoiFilZsl

MinDel

Minimum Delta Z

PoiFilZsl  MinDel -2.0

Point Display Filter - Minimum Delta Z

PoiFilZsl

MaxDel

Maximum Delta Z

PoiFilZsl  MaxDel 5.0

 

 

 

 

 

Point Display Filter - Classification - On/Off

PoiFilCla

On|Off|Tog

 

PoiFilCla  On

Point Display Filter - Classification - Set

PoiFilCla

Set

NumberLine (0-31) On|Off

PoiFilCla  Set  0-5;7;14  On

 

 

 

 

 

Point Display Filter - Return Number - On/Off

PoiFilRet

On|Off|Tog

 

PoiFilRet  On

Point Display Filter - Return Number - Return number to display (0=Last)

PoiFilRet

RetNum

0-5

PoiFilRet  RetNum  0

 

 

 

 

 

Point Display Filter - Sensor Number - On/Off

PoiFilSen

On|Off|Tog

 

PoiFilSen  On

Point Display Filter - Sensor Number - Sensor numbers to display

PoiFilSen

Set

NumberLine (0-7) On|Off

PoiFilSen  Set  0;3-5  On

 

 

 

 

 

Point Display Filter - Flight/Strip Number - On/Off

PoiFilFli

On|Off|Tog

 

PoiFilFli  On

Point Display Filter - Flight/Strip Number - Strip numbers to display

PoiFilFli

Set

NumberLine (0-255) On|Off

PoiFilFli  Set  0-5;7;14  On

 

 

 

 

 

Point Display Filter - GPS Time - On/Off

PoiFilGps

On|Off|Tog

 

PoiFilGps  On

Point Display Filter - GPS Time - Min time to display

PoiFilGps

Min

GPS Time

PoiFilGps  Min  1000

Point Display Filter - GPS Time - Min time to display

PoiFilGps

Max

GPS Time

PoiFilGps  Max  5000

 

 

 

 

 

Point Display Filter - Scan Angle - On/Off

PoiFilSca

On|Off|Tog

 

PoiFilSca  On

Point Display Filter - Scan Angle - Min Scan Angle to display

PoiFilSca

Min

Angle (degrees)

PoiFilSca  Min -20

Point Display Filter - Scan Angle - Max Scan Angle to display

PoiFilSca

Max

Angle (degrees)

PoiFilSca  Max  20

 

 

 

 

 

Point Display Filter - KeyPoint - On/Off

PoiFilKey

On|Off|Tog

 

PoiFilKey  Tog

 

 

 

 

 

Point Display FIlter - Turn all filters off

PoiFilOff

 

 

PoiFilOff

 

 

 

 

 

Point Color Parameters - Entity (Color by layer) - On

PoiColEnt

On

 

PoiColEnt  Off

 

 

 

 

 

Point Color Parameters - Intensity - On

PoiColInt

On

 

PoiColInt  On

Point Color Parameters - Intensity - Intensity minimum

PoiColInt

Min

Intensity

PoiColInt  Min  100

Point Color Parameters - Intensity - Intensity maximum

PoiColInt

Max

Intensity

PoiColInt  Max  4096

Point Color Parameters - Intensity - Start color

PoiColInt

StaCol

R-G-B

PoiColInt  StaCol  20-40-255

Point Color Parameters - Intensity - End color

PoiColInt

EndCol

R-G-B

PoiColInt  EndCol  125-50-255

 

 

 

 

 

Point Color Parameters - Classification - On

PoiColCla

On

 

PoiColCla  On

Point Color Parameters - Classification - Set color

PoiColCla

Col

Classification#  R-G-B

PoiColCla  Col  5  75-0-255

 

 

 

 

 

Point Color Parameters - RGB - On

PoiColRgb

On

 

PoiColRgb  On

 

 

 

 

 

Point Color Parameters - Elevation - On

PoiColEle

On

 

PoiColEle  On

Point Color Parameters - Elevation - Elevation range source

PoiColEle

Sou

Poi | Usr

PoiColEle  Sou  Poi

Point Color Parameters - Elevation - Minimum user defined Z

PoiColEle

MinZ

Elevation

PoiColEle  MinZ  630.0

Point Color Parameters - Elevation - Maximum user defined Z

PoiColEle

MaxZ

Elevation

PoiColEle  MaxZ  860.0

Point Color Parameters - Elevation - Elevation increment (0=none)

PoiColEle

EleInc

ElevationIncrement

PoiColEle  EleInc  5.0

Point Color Parameters - Elevation - Start color for lowest elevation

PoiColEle

StaCol

R-G-B

PoiColEle  StaCol  25-45-75

Point Color Parameters - Elevation - End color for highest elevation

PoiColEle

EndCol

R-G-B

PoiColEle  EndCol  125-50-255

Point Color Parameters - Elevation - Color scale type to use

PoiColEle

ScaTyp

Sca|Usr|Tog (Scale or User)

PoiColEle  ScaTyp  Sca

 

 

 

 

 

Point Color Parameters - Slice - On

PoiColSli

On

 

PoiColSli  On

Point Color Parameters - Slice - Slice elevations

PoiColSli

SliZ

Index  MinZ   MaxZ

PoiColSli  SliZ  10 3000.0  3500.0

Point Color Parameters - Slice - Color for elevation slice

PoiColSli

SliCol

Index   R-G-B

PoiColSli  SliCol  10  120-80-10

Point Color Parameters - Slice - Default color

PoiColSli

DefCol

R-G-B

PoiColSli  DefCol  255-0-255

Point Color Parameters - Slice - Reset elevation parameters

PoiColSli

ResZ

 

PoiColSli  ResZ

 

 

 

 

 

Point Color Parameters - Sensor - On

PoiColSen

On

 

PoiColRgb  On

 

 

 

 

 

Point Color Parameters - Flight/strip Number On

PoiColFli

On

 

PoiColFli  On

 

 

 

 

 

Point Color Parameters - Intensity Drape - On/Off

PoiColIDr

On|Off|Tog

 

PoiColIDr  On

 

Point Display Key-In Parameter Notes

Number Line - Blanks and commas are used to separate commands on a Vr key-in.  When using a number line, semicolons, colons, or stars should be used to separate the fields.  For example: to specify classifications 0, 1, 2, 3, 4, 5, 7, 14, the number line "0-5;7;14" could be used.
Tog - When Tog is listed as a keyword or parameter option, it may be used to toggle the current value.  For example, if the classification filter were turned on, "PoiFilCla Tog" would turn it off.
Red Green Blue (RGB) values - The red, green and blue values that define a color are separated with a dash.  For example, 127-255-212 would define the color aquamarine.
Point Filters - Multiple point filters (PoiFil) can be active.
Point Color - Only one point color (PoCol) mode can be active.  When a mode is selected the previous color mode is de-selected.
Point Color Parameters - Slice - The Index is the elevation slice number.  There may be up to 20 elevation slices.  The range of Index is from 1 to 20.