Working with Bathymetric Data

By: Katrina Schweikert

Global Mapper is well known for its file format support and terrain analysis capabilities. Perhaps what is less well known is the way the various data analysis tools in Global Mapper can be used to generate and analyze bathymetric data. 

Bathymetry is the study of topographic landforms below the water, such as on the ocean floor, the bottom of a lake, or even the bed of a river. Given that over 70% of the earth’s surface is covered with water, this branch of 3D analysis is extremely important in understanding the characteristics of the planet. What follows is an exploration of some of Global Mapper’s analysis and visualization techniques that are relevant to the bathymetric analysis. 

Great Barrier Reef Depth model obtained from Geoscience Australia

Bathymetric Data Support

Global Mapper provides support for over 300 file formats, and many of those include formats for bathymetric data, marine navigation, and remote sensing of subsurface data. Here are some examples: 

  • Marine Navigation and Nautical Charts (S-57 and S-63 with s-52 symbols, NOS/GEO, NV Verlag, PCX,  and others)
  • Sonar, Sidescan sonar and Bathymetric Sounding data (Lowrance Sonar, XTF, HTF, and others) 
  • Gridded Bathymetric Data (BAG, DBDBV, Hypack, IBCOA, GRD98, NITF, various other terrain formats such as netCDF, GeoTiff, ASCII grid)

Bathymetry in a DTM

Gridded bathymetric data provides various visualization and analysis options when loaded into Global Mapper.   The preformatted elevation shaders or a custom shader can be used to find the best color scheme to show depths of submarine landforms. Terrain Shaders can also reveal the slope steepness and slope direction of underwater topography. 

Displayed in the 3D viewer, gridded bathymetric data comes to life with draped imagery and charts, water level visualizations, and any other reference vector data. Quickly and easily generate elevation profiles, or a series of sequential cross-profiles using the Path Profile tool and Perpendicular Profiles setting. 

3D view of bathymetric data with path profile cutaway showing a shipwreck site in the Gulf of Mexico

Combining data from different surveys and fusing data from multiple sensors is as easy as loading in the datasets and ordering the layers. The analysis and visualization tools can automatically merge the various inputs to take data from the topmost layer or choose to view and compare the data from multiple surfaces simultaneously. There are also options for cropping, aligning, feathering, and comparing to create a more seamless integration between disparate datasets. 

Analyzing Bathymetry as a 3D Point Cloud

Global Mapper provides tools for converting existing sensor data such as sonar or soundings to a 3D point cloud; or for sampling existing gridded data to create an array of 3D points at the pixel centers. This enables the automated classification algorithms of the Lidar Module, which can be used to identify the seafloor and identify or remove other subsurface structures or topography. This powerful tool has been used for shipwreck detection and modeling, as well as identification of other subsurface features. 

Subsurface Contouring

Global Mapper includes an easy-to-use tool for generating precise depth contours and shorelines from gridded bathymetric data. The resulting line features can be edited and stylized in a variety of ways and combined with other datasets to create custom bathymetric charts. Alternatively, the areas enclosed by contours lines can be filled to create polygons that show the water extent at different depths or sea levels. 

Contour lines colored by elevation combined with other basemap data to create a custom chart

Measurement and Volume Calculation

Global Mapper provides various tools for calculating two- and three-dimensional measurements. In the 2D map view, the Path Profile window, and the 3D Viewer linear distances and areas are measured using a simple drawing function. Volume can be calculated from bathymetric data by either defining a height or by calculating numerous volumes across a range of water heights. Volume can also be measured by defining a plane or comparing the bathymetric data to a surface grid. This provides various options for water volume calculation. 

Flood Modeling

By combining bathymetric data with terrain data and using tools such as the watershed analysis and water level rise tool it is possible to discover flood extents, flow accumulation, and perform other hydrographic analysis. 

Employing the various terrain editing and terrain creation functions, Global Mapper can be used to create hydro-enforced DEMs or other modified surface models. These can be analyzed within Global Mapper or exported to various formats to support analysis in other applications. 

Temperature and other Measurements

The bathymetric analysis may also involve other gridded datasets such as surface temperature, salinity, gravimetric data, and various other measured values. These datasets can also be visualized, rendered in 3D, and contoured to provide additional insight into the dynamics of lakes, oceans, and other water bodies. 

The latest version of the Global Mapper and Lidar Module include several enhancements, many of which apply to bathymetric data analysis. If this blog piqued your interest and you’d like to find out if Global Mapper is the right application for you, download a 14-day free trial and request a demo today!

How Pixels to Points Works

By: Katrina Schweikert

The Pixels to Points tool in Global Mapper’s Lidar Module uses a process of Automated Aerial Triangulation to reconstruct the 3D scene present in overlapping images. This computationally intensive process may seem like magic, but it relies on basic concepts of vision and photogrammetry. Photogrammetry is the science of taking real-world measurements from photographs. Let’s pull back the curtain to reveal how this process works. 

What is Aerial Triangulation?

Based on photogrammetry techniques, the location, size, and shape of objects can be derived from photographs taken from different angles. By combining views from multiple images, the location of distinct parts of the image are triangulated in 3D space. This is similar to how depth perception works with two eyes; since the object in front of you is viewed from two slightly different angles, the brain can perceive how far away the object is.

Diagram of depth perception

In traditional photogrammetry with stereo-image pairs, the two angles of the image allow the photogrammetrist to measure objects in the image and determine their real world size. With automated techniques using many overlapping images, the entire 3-dimensional nature of the scene being photographed can be reconstructed. 

Photogrammetry measurement diagram

What are the steps in Automated Aerial Triangulation?

Automated Aerial Triangulation involves a number of steps to get from the original images to 3D point clouds, terrain models, textured 3D models, and orthoimages. The first step is to detect distinct features in each image, and then match those features across the adjacent images. The challenge is to automatically detect distinct features that may be at different scales and rotations in each of the images. 

Features detected in two images, with lines showing the matches found

After the features are tracked through the images, the initial reconstruction begins with a process called Structure from Motion (SfM). In the context of mapping technology, the structure of the 3D scene is revealed based on the motion of the camera. This process calculates the precise orientation of the cameras relative to each other and to the scene, and builds the basic surface structure of the scene. This is the point where the selected Analysis Method is applied. The Incremental Analysis Method starts with a set of the best matching photos, and incrementally adds the features from subsequent images into the scene to build the 3D reconstruction. This works well for drone-collected images collected over a large area in a grid pattern. The reconstruction will typically start somewhere near the center of the scene, and work outwards. The Global Method, by contrast, takes information from all of the images together and builds the scene all at once. This makes for a faster process, but it also requires a higher degree of overlap between adjacent images. This is recommended if the images are collected focusing on an object of interest, such as a building, especially when all of the images focus on that central area or object. The result of the Structure from Motion analysis is a sparse point cloud that builds the basic structure of the scene, and a set of precisely oriented cameras that show where and in what direction the images were taken relative to each other

Example of sparse point cloud with camera frustums

The final step of the Automated Aerial Triangulation process involves filling in additional details from each image that was calibrated as part of the scene. This process is called Multi-view Stereo. It involves calculating the depth of each part of the image (i.e. how far away it is from the camera), and then fusing those depth maps to keep the points that appear in multiple images. 

Depth map and confidence map based on overlap with other images

This process generates the final dense 3D point cloud. Based on the options selected, there may be further processing to convert the point cloud into a refined mesh surface (3D Model) that is photo-textured by projecting the images onto it. This option also produces the highest quality orthoimage, removing relief distortions based on the 3D mesh surface. 

What factors impact Automated Aerial Triangulation?

Lens Distortion

An important initial step in the Pixels to Points process is removing the lens distortion in the image. While the photograph may appear as a flat image capture of the target area to the untrained eye, most photographs contain some distortion, particularly towards the edge of the image, where you can see the effect of the curvature of the camera lens. Pixels to Points will remove distortion in the image based on the Camera Type setting. Most standard cameras need correction for the basic radial lens distortion in order to create an accurate 3D scene. The default camera type setting, ‘Pinhole Radial 3’, corrects for the radial lens distortion (using 3 factors). In some cases it might be beneficial to use the ‘Pinhole Brown 2’ camera model, which accounts for both radial distortion and tangential distortion, where the lens and sensor are not perfectly parallel. 

Image with distortion and processed undistorted imag

Some cameras have the ability to perform a calibration, which automatically removes distortion in the image. If the Pixels to Points tool detects from the image metadata that the images have been calibrated, it will switch to the ‘Pinhole’ camera model. If you know your images have already had the distortion removed either by the camera, or some other software, choose the ‘Pinhole’ camera model, which will not apply any additional distortion removal. The final two Camera Type options account for the more extreme distortion of Fisheye or Spherical lenses. Select these options if appropriate for your camera. 

Focal Length and Sensor Width

An important part of transferring the information in the image into a real world scale is knowing some basic camera and image information. The focal length and sensor width values allow for a basic calculation of how large objects are in the image, and thus how far away they are from the camera. What is calculated using these values is a ratio between a known real world size (the sensor width) and the pixel equivalent of that size in the image. This is a starting point for reconstructing the 3D scene. Focal Length information is typically stored in the image metadata. Global Mapper includes a database of sensor widths based on the camera model, however, you may be prompted for this value if your camera is not in the database. You can obtain this information from the device manufacturer. 

Image Position

The basic position of each camera is typically stored in the image metadata (EXIF tags). With a standard camera this location is derived from GPS, from which average horizontal accuracy is within a few meters. There are a few ways to improve the accuracy of the resulting data based on the desired accuracy, and decisions about cost vs. time spent. 

Height Correction

The GPS sensors contained in most cameras may have sufficient horizontal accuracy for some applications. However, the corresponding height values are usually less accurate and are based on an ellipsoidal height model. A basic height correction can be performed using the options for Relative Altitude. This will anchor the output heights based on the ground height where the drone took off (the height of the ground in the first image). You can enter a specific value, or Global Mapper can automatically derive the value from loaded terrain data or online references (USGS NED or SRTM). 

Ground Control Points

One way to correct the position of the output data is through the use of Ground Control Points. This is a set of surveyed points with known X,Y,Z locations that should be evenly distributed throughout the scene. The measured ground control point locations need to be visually identifiable throughout the corresponding images, so it’s common to use a set of crosshairs or targets placed on the ground throughout the collection area before the images are captured.

 

Ground Control Points can be loaded into the Pixels to Points tool and the corresponding locations identified in multiple input images. This will align the scene based on the control points taking precedence over the camera positions. This procedure is a more time-intensive option, but is streamlined through a process whereby the images containing each point are highlighted, It is also possible to use Ground Control Points after the output files have been generated. Global Mapper provides various tools for this, including 3D rectification and the Lidar QC tool, which can also provide accuracy assessment information. 

RTK and PPK Positioning

Hardware manufacturers provide options for improving the accuracy of the positional information by communicating with a reference base station in addition to satellites, and by performing additional corrections based on available information at the time of the image collection. This includes both Real-Time Kinematic and Post-Processing Kinematic options. With some systems, higher accuracy positioning information is written into image metadata, which can be used directly in the Pixels to Points tool. Other systems may save the higher accuracy positions in a text file, in which case you will want to load your images into the Pixels to Points tool and use the option to Load Image Positions from External File

 

Understanding the variables and data requirements for the Pixels to Points tool and other SfM processes will help you to collect images better suited for processing. In turn, this will create higher quality results for further geospatial analysis.

The latest version of the Global Mapper Lidar Module includes several enhancements, many of which apply to the Pixels to Points tool for generating point clouds and 3D meshes from drone-captured images. If this blog piqued your interest and you’d like to find out if the Lidar Module of Global Mapper is the right application for you, download a 14-day free trial and request a demo today!

Classifying Lidar with the push of a (few) button(s)!

By Rachael Landry

If you are working with any type of point cloud data, the Global Mapper Lidar Module is a powerful, must-have add-on to the desktop application. One of the standout features of the Module is its ability to automatically identify and apply the appropriate ASPRS classification to each point with a few clicks. This blog will walk through the steps required to automatically classify a point cloud. 

Global Mapper’s Lidar auto-classification tools provide the means to identify ground, buildings, utility lines and poles, vegetation, and noise points within an unclassified point cloud. Each of the classification processes requires the presence of ground points in the point cloud so this is a good place to start. If necessary, noise classification can be used to automatically identify any points that are beyond the expected elevation range when compared to those in close proximity. This cleanup tool is used to remove obvious anomalies in the data.  At this stage, buildings and trees can be classified and if the point cloud is of sufficient density, there are even tools to classify above-ground utility lines and poles. 

When you begin the auto-classification process and load your point cloud into the software, it is important to know that Global Mapper has the ability to display points in several different ways including by RGB value (if present), intensity, and classification. For this process, we will color the Lidar by classification. If your point cloud has never been classified, it will look similar to this:

*An unclassified point cloud is displayed as gray.

After the data is loaded, you are ready to classify ground points. To do this, locate the Auto-Classify Ground Points button in the toolbar. This tool brings up the Automatic Classification of Ground Points settings window. These values will need to be adjusted based on the local terrain, the range of elevation values in the data set, user-defined preferences for filtering points prior to auto-classification, or known features in the landscape. This will help to optimize the output. When you have applied the necessary settings, click the OK button to initiate the process. 

*A point cloud with classified ground points.

If necessary, your next step will be to click the Auto-Classify Noise Points button. Identifying previously unclassified noise points will clean up the point cloud and improve further classification results. 

At this stage, the non-ground points or points representing buildings and vegetation, are ready to be identified and classified. In the Lidar module, buildings and vegetation are classified using the same algorithm, and the dialog box can be accessed using the Auto-classify Buildings and Vegetation button. The parameters required in the classification process describe the expected structure of buildings and trees within the point cloud. These values can be adjusted to account for the characteristics of your specific point cloud. 

*Point cloud with ground buildings and vegetation classified.

The Auto-Classify Powerline and Pole points button can automatically detect above-ground cables, and/or pole-like objects, such as utility poles, in high-density Lidar data with at least 20 points /m2. This density is typical of terrestrial Lidar and mobile Lidar point clouds. While synthetic Lidar (photogenerated Lidar) may also have this density, it does not typically have the reconstruction detail to precisely identify power lines or pole-like objects. Similar to the other classification tools, this process looks for structures resembling powerlines or poles based on user settings.

After you have classified your point cloud, you can begin analyzing the data further. This may involve creating a terrain model or extracting vector features from the classified point cloud.

Keep an eye out for our upcoming blog, focused on the lidar QC process! 

To learn more about the Lidar Module’s automatic classification tools please check out the Global Mapper Knowledge Base and if you have any further questions about the auto-classify tools please contact geohelp@bluemarblegeo.com.

Getting to Know the Global Mapper Toolbars

Written by: Cíntia Miranda, Director of Marketing

Global Mapper is a robust and yet easy-to-use GIS application that offers access to an unparalleled variety of spatial datasets, a complete suite of vector and raster processing tools, and an extensive collection of analysis tools, especially for working with Lidar or terrain data. If you’re new to Global Mapper, getting to know the toolbar is one of your first steps in familiarizing yourself with the application.  This blog provides a brief review of the buttons to help you understand the basic function of each.  More in-depth information is available in the Knowledge Base

The toolbars in Global Mapper provide quick and easy access to the most commonly used tools. To hide or display the toolbars, click the View menu and, from the Toolbars submenu, check or uncheck the appropriate checkboxes as needed.

The drop-down menu on the right side of each toolbar provides access to Customization of the toolbars, including adding new buttons and showing text labels.

Note that some toolbar buttons will not be available in certain situations. For example, most of the Digitizer (Edit) buttons will be disabled until one or more vector features are selected on the map.

Here’s what each toolbar button can do for you:

File

Open Data Files  Save Workspace  

Connect to Online Data  Map Layout Editor  

 Overlay Control CenterConfigure

 Overview Map

Navigation

Zoom (Alt+Z)Pan (Alt+G)

Zoom InZoom Out

Restore Last View (Ctrl+Backspace)Full View

Selection

Digitizer Tool (Alt+D)Select by Drawing Polygon

Clear Current SelectionSelect Labels

Tools

Measure Tool (Alt+M)Feature Info Tool (Alt+P)

Search Vector Data

Analysis

Create Elevation GridCreate Contours

Calculate Cut and Fill Volume (Ctrl+Alt+M)Path Profile (Alt+L)

Create View Shed (Alt+V)Create Water Shed

Combine/ Compare Terrain LayersCombine/ Compare Terrain Layers

Create 3D Fly-through

Viewer

Add 2D Map ViewsRotate Map

Image SwipeShow 3D View

Link 2D and 3D Views (Ctrl+Shift+3)Display Water Level

Increase Water LevelDecrease Water Level

Enable/ Disable Hill ShadingDynamic Hill Shading

Shader Drop-down Menu

GeoCalc

Enable GeoCalc Projection ModeAuto-select GeoCalc Transform

Launch Geographic Calculator

Favorites

Favorites Drop-down

Run Selected Command (Ctrl+Enter)

Digitizer (Create)

Create Point/ Text FeatureCreate Line Feature (Vertex Mode)

Create Line Feature (Trace Mode) (Shift+T)Create Area Feature

Create Rectangle/ Square Area FeatureCreate Circle/ Ellipse Area Feature

Digitizer (Advanced)

Create Distance/ Bearing/ COGO LineCreate Range Rings / Ellipses

Create Regular Grid of FeaturesCreate Strike-and-Dip Point

Cut Selected Area(s) From Another AreaRight Angle Draw Mode (R)

Ortho Draw Mode

Digitizer (Edit)

Move Selected Feature(s) (Ctrl+Shift+M)Rotate Scale Feature(s)

Display Area/ Line Vertices (Shift+V)Move Selected Vertices

Insert VertexCombine Line Features

Split Line At Selected VertexCreate Points From Line/ Area Vertices

Create Areas From LinesCreate Lines From Areas

Combine Selected AreasCrop To Selected Areas

Create Buffer Around Selected Features

GPS

Start Tracking GPS (Ctrl+T)Stop Tracking GPS

Keep GPS\ Video Vessel on screenOrient View to GPS \Video Heading

Mark Waypoint (Ctrl+M)Mark Waypoint from Averaged Position

Mark Waypoint at OffsetDisplay GPS Info

Animate

StartStop

SlowerFaster

AddRemove

Get the most of Global Mapper by learning how it can improve productivity, encourage efficiency, and save time and money in your GIS operations.  The following resources will help you become familiar and more proficient with the software.

1) The Global Mapper Getting Started Guide provides a concise overview of the software.

2) The Global Mapper Knowledge Base has more in-depth information about Global Mapper’s features and functions.

3) The FAQ page offers answers to commonly asked questions.

4) The self-guided training provides a series of free hands-on exercises, including written instructions and sample data files. Take a moment to download these instructional materials to learn how to use some of Global Mapper’s basic tools. 

5) The GeoTalks Express webinars are a series of free online presentations conducted every two weeks covering a wide variety of topics and themes. Sign-up to one or multiple webinars! 

6) Global Mapper online training classes provide the most effective way to get the most out of the software. Scheduled public classes provide a thorough introduction to the full breadth of the application’s features and functions, while a custom class will allow your organization to adapt the course content to meet your specific needs. For more information, email training@bluemarblegeo.co

Global Mapper’s intuitive user interface and logical layout help smooth the learning curve and ensures that users will be up-and-running in no time. Take advantage of the aforementioned resources and if you need any further assistance with the application, contact geohelp@bluemarblegeo.com.

How to Activate Global Mapper Single-User License

By Rachael Landry

The Global Mapper single-user licensing process begins with an email. When a purchase is completed, an order confirmation email is automatically sent with information and instructions on how to license the software, including links to download Global Mapper, information about how to become a registered user, and access to detailed instructions on how to activate the license. The email also provides the order number for the purchase, which is used to activate single-user licenses via the internet.

*It is important to note that the email is generally sent to the purchaser unless otherwise requested. Please keep this in mind if the software was purchased by your company the licensing email may have been sent to the purchasing department and not the end-user.

After reviewing the order confirmation email, the next step is to download Global Mapper and open the application. The software will open with the License Global Mapper dialog box where you enter your user information (make sure to enter the same information you use to login to the Blue Marble website). If you are not a registered user, follow this link to register before proceeding. Then select the Activate single-user or trial license option, and click the Continue button.

In the next dialog box, select the Single user license option and enter your complete order number. Note that this field is case-sensitive. This dialog box also allows users who purchased Global Mapper and the optional Lidar Module in the same order to license it at the same time. Finally, click the “Continue” button to complete the licensing process.

After your copy of Global Mapper has been registered, please be sure to check out all of Blue Marble’s Global Mapper resources. From the YouTube page to the self-guided training, and bi-monthly webinars, Blue Marble wants to provide you with the tools to ensure that you are using Global Mapper to the fullest. 

If you have any questions or issues activating your license please contact authorize@bluemarblegeo.com.

What’s new in Global Mapper Mobile version 2.1

Written by: Cíntia Miranda, Director of Marketing

If you don’t have Global Mapper Mobile® on your phone or tablet, you’re missing out on a great opportunity to expand the reach of your GIS operations – for free!  Global Mapper Mobile is a powerful iOS and Android application for viewing and collecting GIS data.  It utilizes the GPS capabilities of mobile devices to provide situational awareness and locational intelligence for remote mapping projects. The mobile application provides maps-in-hand functionality for engineers, surveyors, wildlife managers, foresters, and anyone whose job requires access to spatial data in remote locations.

A complement to the desktop version of Global Mapper®, the mobile edition can display all of the supported vector, raster, and elevation data formats and offers a powerful and efficient data collection tool. The 2.1 release includes several new enhancements including:

  • Vector feature styling improvements with an increase in the number of built-in supported vector styles and expanded support for custom symbols. Feature styles can now be previewed when creating or editing a feature as well.
  • Terrain layers are now rendered with hill shading and a default color shader and elevation values can be viewed from elevation layers at a specific location. 
In addition to being able to render terrain data with hills shading and a terrain shader, the app will now display the terrain layer’s elevation value when in crosshair location mode.
  • A new option to set the layer transparency for raster and terrain layers. This latest release also features an improved color picker and support for Dark Mode.
The new Shortcut Bar (upper left) allows for quick access to Advanced GPS functionality and zooming/panning tools

For advanced field mapping applications, a Pro version of Global Mapper Mobile is available for only $50. Version 2.1 of Global Mapper Mobile Pro includes all of the capabilities of the free version and it also offers:

  • Advanced GPS support allowing users to connect to external high accuracy Bluetooth GPS devices, from vendors such as the Bad Elf and Juniper. This functionality allows users to access detailed information from these devices including the ability to view satellites, detailed location information, and even view/record the NMEA stream.  
Once an external GPS device is connected to the app, the Advanced GPS functionality allows the user to view detailed location information and check on a satellite connection, along with viewing and saving the NMEA stream.
  • A new configuration option that allows Pro users to select and change the terrain shader directly within the application.
  • Water display enablement to render the simulated water level over the loaded terrain data at a given elevation to visualize potential flooding.

If you’re already using Global Mapper Mobile, update to version 2.1 now!  If you haven’t tried it yet, download the app today and expand the reach of your GIS operations.

 

Try Global Mapper Mobile v.2.1 today!

[Download (iOS)]        [Download (Android)]

Elevation Grid Creation in Global Mapper: Creating a DTM

Written by: Mackenzie Mills,  Application Specialist

The Elevation Grid Creation tool in Global Mapper uses loaded 3D data, data with x, y, and z values, to create a raster gridded elevation layer. This layer can then be exported in one of the supported elevation formats, or used for further analysis or to create a map.

A generated elevation grid layer displayed in the 3D viewer. 

The first method Global Mapper offers to generate elevation grid layers is the Triangulated Irregular Network or TIN method. This method connects 3D point features or the vertices of 3D line and area features into a network of triangles. From there, the program interpolates over the triangular faces using the feature elevation and slope values to generate an elevation grid layer.

Triangulation Method Process: Source Contour Line Data, Contour Lines with Vertices connected by the Triangulation Network, Triangulation Network with Interpolated Raster Grid, Output Gridded Elevation Layer.

With the Lidar Module, Global Mapper not only provides point cloud classification and processing tools, but the program also provides additional methods for generating an elevation grid. These additional options are all variations on the binning method. This method is better suited for point cloud processing because not every single point in the point cloud is used to generate the output grid.

Typically point clouds are quite dense and you don’t need to use every single value to generate an accurate output. In fact, using every point often results in an elevation grid layer that contains lots of noise and appears rougher than the actual study area. The binning methods help to reduce this noise by spatially binning the data into areas corresponding with the size of the output grid cells. One value from each of the spatial bins is then used to generate the gridded layer. The elevation value from each bin that is used to generate the grid is determined by the specific binning method that is selected. For example, the Binning Minimum Value method uses the minimum elevation value from each bin to generate the grid. The Lidar Module currently offers three variations on the binning method, with two additional variations coming soon.

  • Binning (Minimum Value – DTM)
  • Binning (Average Value)
  • Binning (Maximum Value – DSM)
  • Coming Soon – Binning (Median Value)
  • Coming Soon – Binning (Variance)
Elevation Grid Creation dialog from left to right: Using only 3D Line or Area Features, Triangulation Method Selected using a Point Cloud, A Binning Method Selected using a Point Cloud.

A digital terrain model, commonly referred to as a DTM, is an elevation model that describes the terrain or ground of an area as opposed to the structures and features on top of the ground, such as buildings and vegetation. Conversely, a digital surface model, or DSM, aims to show the structures and features on top of the ground.

When creating a DTM, you will likely want to use the binning minimum value method. Since lidar is not ground-penetrating, the minimum values detected in the point cloud are most likely to be true ground measurements.

Another option you have in your workflow is to further identify ground points by classifying your point cloud using the classification tools available in the Lidar Module. The automatic classification tools allow you to perform rough classifications that you can then clean up and fine-tune with manual classification.

When generating the elevation grid layer, there is the option to further filter the points of your point cloud to use only points within a specific class, with specific flags, or in a designated elevation range. This filtering will help to further narrow down the points available to consider when Global Mapper is building the elevation grid layer.

The Filter Lidar Points dialog accessed from the Elevation Grid Creation Options.

Water bodies such as ponds, lakes, and rivers may not provide consistent point cloud data. When generating an elevation grid that contains water-covered areas, you may want to flatten those areas to a specified elevation value. This can be done by including a 3D area feature in the data used to create the grid, and using the grid creation option to ‘Use 3D Area/Line Features as Breaklines’. This will burn the area feature into the output grid at the elevation designated by the area feature, thus flattening the noise within the area. This can be used for road features, building footprints, or any other area features as well.

A path profile showing the point cloud and generated terrain grid that used a breakline to flatten the water area, and the same grid in the 3D viewer showing the flattened water area and rockier shore. 

To compare a few different elevation grid creation methods, the path profile tool can be used. Below is a path profile over three elevation grids all using different methods. You can see that the binning method grid appears smooth compared to the triangulation method grid.

A Path Profile Comparing Generated Elevation Grids

With an elevation grid layer created to show the elevation as a surface, you can continue your analysis in Global Mapper to generate contour lines, generate watershed areas, perform volume calculations, or any other analysis function. To see more of what Global Mapper can do for you, please visit the Tips & Tricks page or request a demo or a trial today.

Try before you buy: Blue Marble Geographics trial licenses

Written by: Rachael Landry

Blue Marble Geographics offers trial licenses for both Global Mapper and Geographic Calculator to give you a chance to evaluate the products and to be sure that what you are purchasing meets your needs. There are two easy ways to receive a trial license for each product. 

The most popular way to access a trial license is through the website, which can be done by following these directions:

  1. Begin by visiting the website and logging into your Blue Marble account. 
    1. If you don’t have an account, make one before proceeding 
    2. If you can’t remember your password, you can reset it here 
  2. Once you have logged into your account, navigate to the download page
    1. For Global Mapper, click here
    2. For Geographic Calculator, click here 
  3. Select the product you want to try and download it
  4. Once the download is complete, install the software and a registration dialog box will appear
  5. Enter your Blue Marble Geographics account information and click the Next button
  6. Select the Trial license type. 
  7. Select any additional products for which you would like to request a trial license, such as the Lidar Module
  8. Press Continue to activate the trial license. 

The second way to receive a trial license is via email, using offline activation. Although you will still need to download the software, you can email authorize@bluemarblegeo.com to request the actual license file. The licensing team will help walk you through the activation process.  

If you have any questions about obtaining a trial license, please email authorize@bluemarblegeo.com