High resolution terrain data is more accessible than ever. There are various open data LiDAR initiatives for example 3DEP or NOAA(coastal) in the USA, Kortforsyningen in Denmark, Environmental Agency LiDAR data in the UK, Gipuzkoa in Northern Spain, a quick Google search throws up many sources of LiDAR data, not to mention the relative ease and low cost of project based capture. High resolution terrain models can even be generated via drones using traditional photogrammetry techniques.
Often the end product be it DSM or DTM is often supplied in a format fit for import in to GIS platforms. Due to the large size of these files some GIS platforms can struggle to display them efficiently. This could be said about older versions of MapInfo, in recent versions however MapInfo’s MRR and improved handling of large raster files has made this a problem of the past.
It is important to understand how MapInfo Pro and MapInfo Pro Advanced differ in regard to MRR and large raster file handling. The first thing to note is that a large raster file does not have to be converted in to an MRR format from its original format in order to benefit from the improvements in MapInfo raster file handling. MapInfo Pro and MapInfo Pro Advanced both utilise pyramiding for the rendering of large files. You will notice in file explorer a new file with the suffix .ghx, this is created as a file is opened and contains precomputed grid statistics that ultimately improve the performance and rendering of the file. This is a default action that occurs when a supported grid format is opened in MapInfo, it removes the job of choosing these setting from the user.
MapInfo Pro is able to do this when opening grid files, meaning that users do not need Advanced in order to have visual performance improvements, MapInfo Pro also supports the MRR format. The benefit over the other grid formats include performance improvements as file sizes get larger, aside from this there is the ability to handle multiple bands of data. An easy way to understand what this means is to imagine three grid files of the same resolution all covering the same area. one grid might represent elevation, the second might represent slope and the third aspect. All of these files can be combined together in to a single MRR file. This allows a user to package all of their raster layers for a project area into one file reducing file management issues. It also allows the user to toggle through the layers in the user interface of the Raster tab, alongside accessing and querying the three grids together in the grid calculator. Another benefit includes handling multi or hyperspectral imagery that contains multiple bandwidths for a single image area of interest, to read more on this see this article.
In order to manipulate LiDAR data or derive new products such as contours or surface calculations open the files in to MapInfo Pro Advanced.
Go to File Open > File of Type = Raster Image. Click Open. In this example surface analytics will be discussed.
Go to the Raster tab.
To create a slope grid, select Surface. Surface contains all options for slope and aspect processing.
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Select the Input file (as with other tools in Surfaces, the files does not need to be displayed in a map window, or can even be opened via the file open button in the Surface Analysis callout).
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Set the Surface Analysis choice as required for the relevant output and choose degree or percentage. Slope and Aspect are simple concepts to understand so will not be covered here. To create them, follow the above steps and click Process.
One less obvious option is Curvature. It can sometimes be a misunderstood option in the Surface Analysis toolbox. Curvature calculates the curvature of the surface, is it concave, convex or linear, converging, diverging? What combinations of these does the terrain model incorporate and why are they important?
There are two quite straightforward ways to look at this, one is visualisation enhancement and one relates to movement of surface features.
Firstly, Curvature models can be utilised to greatly enhance how a terrain model appears. For example, the image below is the same elevation model. However, for the left part of the image, a ‘Surface’ Curvature grid has been created (greyscale colour in this example). This grid highlights the curvature of the surface rather than just the elevation values seen in a regular terrain model. Once the two have been layered on and the transparencies adjusted, the viewer can see an incredible amount more detail and information about the actual surface of the land.
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Secondly, in regard to analysing the surface and understanding where any loose surface phenomena may be transported it is easy to make a visual estimation of direction of travel based on the curvature view.
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A more scientific estimation is to use the grid values to understand if the slopes are converging or diverging, splitting movable surface materials in different directions or illustrating where it is likely to collect. A classified map can then be created based on these areas of potential routes transportation, movement or deposits. These types of surface can be combined with land class grids in order to model possibilities of change in the physical terrain.