Use this function for the following:
To generate the grid surface model (grid of the desired size with terrain elevations at intersection points of grid lines) of the terrain for a defined terrain area or for the selected laser scan data file.
Grid surface models can be generated from the following source data:
Current terrain model - The terrain data available in the terrain model
Laserscan Data files - The laser scanned data files in XYZ format (txt files) or raster files (*.LAS files)
The intersection of the horizontal and vertical lines of the grid will be having terrain heights calculated by the Novapoint program based on the heights of the terrain points in the vicinity of the intersection.
The function reads the terrain data from the active database to generate the grid model and hence it is required to check the project setting.
Run the function from:
MOUS_ICO Menu: Terrain > Volume Calculations > Make Grid
MOUS_ICO Toolbar: Volume Calculation: Make Grid
MOUS_ICO Menu: Novapoint > Terrain Model > Grid Model
MOUS_ICO Toolbar: Terrain Model: Grid Model
When this function is activated, Command prompts for:
First corner for DTM View:
MOUS_ICO Pick the lower left corner for the boundary of the data, for which grid model is to be generated.
To generate the grid model, the area, for which the grid model is to be generated, must be defined. A grid model can be generated for the entire data (all groups) available in the database.
Command prompts for:
Other corner for DTM View:
MOUS_ICO Pick the upper right corner for the boundary of the data, for which grid model is to be generated.
Correct corners can be selected if the data, for which grid model is to be generated, is available on the current drawing. Desired data (available in the database) can be drawn to the current drawing using the function 'Draw Map from Terrain Model' of the menu Novapoint Map. Command prompts for:
Draw frame (Yes/No) <No>:
A frame can be drawn to the current drawing to represent the DTM view with the option 'Yes'.
The lower left and upper right corners of the DTM view can also be defined in the dialog box 'Grid Model', which will pop up in this function.
The dialog 'Create Grid Surface Model' will pop up.
Select the source data and confirm the selection using 'OK'.
Refer to the topic 'Grid Model from Current Terrain Model' below for further procedures for creating a grid surface model for the terrain data available in the current terrain model.
Refer to the topic 'Grid Model from Laser Scan Data' below for further procedures for creating a grid surface model using laser scan data as source data.
Grid Model from Current Terrain Model
Generate a grid surface model
Use these steps to generate a grid surface model from the data active in the current terrain model.
Run the function 'Grid Model'.
Select 'Current Terrain Model' as source data on the dialog 'Create Grid Surface Model'.
Confirm the selection with 'OK'. The dialog box 'Grid Modelling' will pop up.
Select options from the three tabs: 'General', 'Settings', and 'Border Coordinates'.
Terrain Model - Displays the name of the active terrain model (database).
Grid File - The grid model being generated will be saved to a file (RUT file). The name of the grid file is to be defined using this option. Click the icon to define the grid file name. The dialog box 'Select' will pop up. Browse to the location where the grid file is to be saved and name the file to create a new RUT file. If an existing RUT file is to be upgraded, select the existing RUT file. If an existing grid file is selected, the program overwrites the existing file by default. You can opt to overwrite or supplement the existing file. Mark the desired radio button on the dialog box. The default option is 'Overwrite the exiting file'.
All active groups (layers) are calculated at the same time and stored in the same grid file. All calculated levels are physically put one after another in the grid file.
Interpolation - There are two methods available for calculating the terrain heights at the intersection of grid lines. Select the desired method of interpolation.
Grid Size - Grid size is normally set in between 2.0 and 10.0m. The grid is always set up with parallel axes. The unit of measurement is meters.
Level - Adjust the lowest level on models with level > 0: If level »0 is used to prioritize heights over level 0, the heights in level 0 are replaced by heights from a group with higher priority.
Adjust level 0 on models with code AL - The terrain surface will be adjusted so that layers that are underground will not come above the terrain surface.
Feature Code and Group Settings - Initiates the 'Terrain Model Properties' dialog box to change the settings such as Active/Passive, Breakline On/Off, Elevations Include/Ignore, etc.
An area of terrain data in the database must be indicated for which grid model is to be generated (when a new grid file is established).
Full model - Fills in the smallest and largest x and y coordinates in the database.
Last View - Fills in the areas for coordinates for the last drawn section.
Manual punching - Ordered section must be acceptable lower left and upper right coordinates.
When supplementing i.e. grid file the sections will be locked to the values of the grid file.
Starts grid generation. The program will first generate grids along the x-axis and then along the y-axis. Grid generation can take some time if there is a large amount of data (large terrain models or small grid size). The program will advise of the number of grid squares and which level is being calculated.
Boundary lines in grid model
Using boundary lines to create holes in the grid model - only grid outside of boundary line (s):
You can use more the one boundary line, but the following must be defined:
Boundary line group must have a priority higher than the terrain
Boundary line group must have type Polygon
Boundary line must be a 3D line
The boundary line can be created using either the create line (Define as Boundary line) function in View / Edit or by creating a polyline in AutoCAD and using the function 'Save Boundary Line to Terrain Model'.
Using boundary line to limit the grid model - only grid inside of boundary line
Only applies to one boundary line
Boundary line must be created as a polyline in AutoCAD, and saved to the terrain model using the function 'Save Boundary Line to Terrain Model'. The polyline can be either 2D or a 3D polyline
Boundary line group must have type Terrain and the same priority as the terrain
Limitations: A grid can be generated for a maximum of 20 layers (Levels), with a maximum of 5000 x 5000 grid squares per layer.
Levels: When applying a grid to terrain, in which Level 1, 2, etc. have been used, all Levels greater than 0 can be inserted in the grid file together with Level 0, replacing the heights contained there.
Transfer to the terrain model: The grid file can be transferred to the terrain model like lines under “Import”. These lines can be used as a base for promotion. The grid file must be a “RUT” file extension.
For grid modeling, either the point grid (P) OR terrain line (L) method must be selected. If one Level is to be grid modeled on point grid and another on lines, this may be carried out in two stages. The methods cannot be mixed within one and the same Level.
Figure: Method L. Points 1 to 7 are interpolated heights in terrain lines. Points Z1 to Z4 are calculated heights based on grid intersections.
In method L, intersections are sought between terrain lines in both X and Y directions. The height of grid intersections is found by weighting the interpolated terrain line heights with the inverse distance from the grid intersection, e.g. Z3 (1,4), Z2 (5,6,7), Z1 (1,2,3,4). If only one (Z4) or no terrain lines coincide(s), the height will remain undefined.
Figure: Method P. Points 1 to 5 are survey points, Points Z1 to Z3 are calculated grid heights.
In method P, the calculation is done in 2 phases. In the first phase, all points nearer the grid intersection than the grid size are weighted with the inverse distance to the grid intersection. There is no limit on the number of points being used, but there must be at least one. Point Z3 will therefore not be assigned a height in the first phase.
In phase 2, lines between two neighboring grid intersections with heights calculated from phase 1 are considered to be terrain lines. The same technique as in method T is used on these “terrain lines”, in this way “islands” of non-defined grid points will later be assigned a calculated height.
Grid Model from Laser Scan Data
The method of this function: Laser scanned data in XYZ format (text file with Northing, Easting, and Elevation coordinates) or Binary LAS - the format is analyzed, converted, and saved as grid files.
The generated grid files (*.RUT) will be saved outside the terrain model. The only data that is saved to the current terrain model is a boundary line (frame) of each grid file and a link in between them. The advantage of this method is that it handles large laser scan data in the terrain model at a very fast rate. The method has been used on several projects with good results.
Other Terrain Model functions that can use the Laser Scan data
The 'View/Edit' function can be used to view the grid boundaries. Use this link for an example.
All the usual functions of 'View/Edit' that read data from the terrain model can be used for Laser Scan Data. This includes functions for generating terrain cross-sections, terrain profiles, alignment design Road Professional and all functions under terrain information under the menu 'Novapoint'. One can also draw a map of the terrain mode as usual.
Triangulation will not work with this method. Generating a grid file based on the terrain model will not work either.
To generate a grid surface model from Laser Scan Data, run the function 'Grid Model', select 'Laser Scan Data' as source data on the dialog 'Create Grid Surface Model', and confirm the selection with 'OK'. A new dialog 'Create Grid Surface Model' will pop up.
Laser scan data available in the ASCII format or in the Binary LAS format can be selected source data for generating the grid surface model. Select the suitable format.
ASCII XYZ format:
Define how the coordinates are presented in the source data file (i.e., East, North, Level OR North, East, Level).
By default, the source data is treated as 'East', 'North', and 'Level', which is the standard practice in Norway.
If the coordinates presentation is not known, the best way to find it out is to open the source file in a text editor (Wordpad, Notepad, etc.,) and check the data. Normally there is a large difference in the East and North coordinates and it will be easy to see this in the source file.
Invert Levels: Use this option to change the sign of the elevation value. Invert levels will then put a minus sign in front of all elevation values. The terrain model will then be able to work properly with both the elevation values above and below the water surface.
Binary LAS format:
Use this option to use binary LAS format as source data for creating a grid surface model.
The default values for grid size, group number of the boundary line of each grid file being saved to the active terrain model, and feature code of boundary line being saved to the active terrain model are to be defined here. The same values will be displayed in the main dialog and can be changed if necessary.
Confirm the details defined in the above dialog using 'OK' to select the source data files. The dialog 'Open' will pop up, select the format at the field 'Files of Type', browse the source file location, select the source file(s) and confirm the selection using 'Open'. Multiple files can be selected using 'Control' and/or 'Shift' keys. The dialog 'Create Grid Surface model' will pop up.
File Name - The selected source files will be listed in this column.
To change a value, click in the cell and key in the new value. It is also possible to 'drag' the values of one field to the other fields in the column.
Grid Size - Define the grid spacing for each source file. The value defined as the default value will be the grid size for all the source files.
Group Number - Define the group number for the boundary line of the grid model being saved to the active terrain model. The group number defined as the default value earlier will be the group number for the first source files and the group numbers for the other source file will depend on the increment defined earlier (Default values).
Existing groups in the terrain model can be selected using the shortcut menu option 'Select Group'. The dialog 'Terrain Model Properties-Groups' will pop up.
Feature Code - Define the feature code for the boundary line of the grid model being saved to the active terrain model. The feature code defined earlier (Default values) will be the feature code for all the source files.
Feature codes can also be defined using the shortcut menu option 'Select Feature Code'. The dialog 'Terrain Model Properties-Feature Codes' will pop up
Shortcut menu options - Place the cursor in the tabular area and activate the shortcut menu.
Remove: To remove the source file.
Use this option to simplify the process of defining the parameters in the main dialog. The dialog 'Dialog' will pop up with the button 'Autofill' or the shortcut menu option 'Autofill'. In this dialog, one can automatically fill the grid size, feature code, and group number.
To activate the autofill option for group number, mark the check box 'Autofill Group'.
Stepwise fill: Use this method to specify different groups for different source data files (grid files) based on the first group number value and the increment specified.
Uniform group number: Use this method to specify the same group number for the source data files (grid files). Define the group number or select an existing group using the ellipse button. The dialog 'Terrain Model Properties-Groups' will pop up with the ellipse button.
To activate the autofill option for the feature code, mark the check box 'Autofill Feature Code'. The same feature code will be adopted for all the source data files (grid files). Define the feature code in the edit field. Feature code can also be specified using the ellipse button. The dialog 'Terrain Model Properties-Feature Codes' will pop up with the ellipse button.
Confirm the values using 'OK' and get back to the main dialog.
E.g.: Use this link to view the dialog of Autofill with a set of values and its result in the main (above) dialog.
Use the button in this column to start the analysis. The analysis will be done based on the specified grid size. After the analysis is complete the analysis result will be displayed in a log file (Analysis.LOG). Use this link to view an example.
The information here is mainly a status of the source file analyzed with Filename, the extent of coordinates X, Y, and Z as well as grid size and the number of points in the file.
The most interesting information is Grid cells with more than 1 point in percent and percent of empty grid cells.
Based on this information, one can judge the effectiveness of the grid size. In case, the grid size is not effective, one can re-analyze the source file for a new grid size by keying the new value in the 'Grid Size' cell.
The connection between grid cells with > 1 point and empty grid cells
Experience from projects using this method indicates that Grid cells with > 1 point should be 10-15%. At the same time, the value of empty grid cells should not exceed 50-60%. This means that several grid sizes are to be analyzed to find the optimal grid size.
Grid size is limited to one decimal.
E.g. 1: For a grid size of 1.0, the analysis results indicate that the grid size is too large. The grid size is changed to 0.3 and analyzed again. Use this link to view the results of a grid analysis for grid sizes 1.0 and 0.3.
E.g. 2: For a grid size of 0.3, the analysis results indicate that the grid size is too small. The gird size is changed to 0.4 and analyzed again. Use this link to view the results of a grid analysis for grid sizes 0.3 and 0.4.
The results indicate that the grid size of 0.4 is optimal.
Use the button of this column for a preview of the contents of the grid file.
The preview is generated with colors indicating the elevation difference. All the points are sorted into 7 colors based on the elevations. Brown is the highest elevation and light green is the lowest elevation. Each interval is 1/7th of the elevation difference within the point in the source file. Use this link for an example of the preview in the window 'Point Viewer'.
Zoom and Pan Options - Use the mouse wheel for the dynamic zoom option. Holding down the left mouse button will define a window to zoom into. Use the key 'P' to zoom in to the previous window. Use the key 'E' to zoom to Extents. Hold down the mouse well and drag the mouse to the preview.
Close the dialog using the button 'X' in the upper right corner of the dialog.
Use the key 'S' to get statistical information. Use this link for an example of statistic information in the dialog 'Point Viewer'. The dialog shows the percentage of grids (vertical scale) and the number of points in the grid. The example above shows that 55% of the grids have 0 points and 10% of the grids have 2 points.
Use the key 'R' to go back to the previous dialog or close the dialog use the button 'X' in the upper right corner of the dialog.
Save to DTM as a linked object - Use this option to save the generated data on grid files with a link to the grid files in the terrain model.
Save as grid file only - Use this option to save the generated data on grid files with no link to the grid files in the terrain model.
Calculate empty grid cells: Mark this check box to fill the empty grid cells within the model as long as the function finds terrain information on all four sides of the empty cells. Empty grid cells in the outer boundary of the model will not be filled.
Grid file Folder - Define the grid file folder (name). By default, the name of the terrain model will be considered as the grid file name. In the above dialog (main dialog) the terrain model is named LASERSCAN and this will automatically generate a subfolder called laserscan and place all the generated grid files (*.rut) to this folder.
The grid file name will be as that of the source data file but the extension of the grid file will RUT. In the above dialog (main dialog) as the source files are E6_0011.TXT; the grid file name will be E6_0011<Postfix>.RUT.
Grid file Postfix - Define post fix for the grid files. E.g: Postfix Test will give a grid file name of E6_0011Test.RUT
E.g.: In the above main dialog, five source data files are selected/listed and as per the values defined in the main dialog (shown above), the grid files will be placed in the subfolder LASERSCAN and will be named as follows:
E6_0011.RUT; E6_0012.RUT; E6_0013.RUT; E6_0014.RUT; E6_0015.RUT;
Use this button to start generating the grid files. The status will be displayed in the dialog 'Calculation'.
Mark the check box 'Launch Report' and click 'OK' to obtain the log file (as shown below) and exit the function. Use this link to view the dialog 'Calculation' and the log file of generation grid files.
The 'View/Edit' function can be used to view the grid boundaries. Use this link for an example. Use the shortcut menu option 'Object report' on this boundary line to obtain a report on the grid data within the boundary line.