Global Mapper Volume Calculation
Jenelle Centeno
The commands to measure or calculate the volume between surfaces commands allow you to calculate the volume of material between two terrains or surfaces. Pile volume and cut and fill calculations are frequently used for determining the costs associated with moving material to or from a specific site, but may also be used for estimating agricultural yields, and determining the impact of a landslide event by comparing before and after volumetric calculations.
The Measure Volume Between Surfaces..., VOLUME - Measure Volume (Cut and Fill), and Pile Volume volumetric calculations work by dividing the area of interest up in to small rectangular pieces, and then calculating the sum volume of the small 3D rectangles between the two terrain models (Measure Volumes Between Surfaces) or the terrain model and the cut surface (Cut and Fill or Pile Volumes).
VOLUME - Measure Volume is found in the Analysis/Measurement Digitizer right-click menu and will measure the cut and fill volume relative to how the vertices of selected feature intersect with a terrain surface. This option has numerous options for editing vertices, base height values, and options to further define the volumetric calculation.
PILE VOLUMES - Calculate the Volume of Selected Piles allows you to quickly measure the volume of selected piles, as defined by the selected area features. This option is also on the Analysis/Measurement Digitizer right-click menu.
Measure Volume Between Two Surfaces... can used to measure the volume between two terrain surfaces loaded in the workspace, the boundaries for the calculation are the edges of the terrain models. This option is found under the Analysis Menu.
If you have one or more line or area features selected with the Digitizer tool, use the right-click menu to access VOLUME - Measure Volume (Cut and Fill) under the Analysis/Measurement right-click menu. This will generate the Volume Calculation Parameters Setup dialog (below) and measure the cut and fill volume relative to how the edges / vertices of the area feature(s) cut the terrain surface.
In the Volume Calculation Parameter Setup dialog you can specify the calculation type, sample spacing, and volume units. Additionally, the base height can specified for all vertices, or for each vertex in the selected feature.
Volume Calculation Type - Allows you to use a line feature to define the area for the cut and fill calculation by setting up a corridor, or an area feature for use in selling up a calculation.
Sample Spacing - Here you can manually specify the sample spacing to be used for determining volumes, with a large area defined over a high resolution terrain model using small values can increase processing time. Use the Projection dialog to edit the linear ground units.
Base Height for Volume Calculations - Allows you to manually set the base height for volume calculations, areas above the base height will be the cut volume and areas below the base height will be considered fill volumes. With the Above Ground option selected for use with Use Same Base Height for All Vertices or Perform Multiple Calculations Over a Range of Base Heights options, the base height will be determined by the user-defined height above ground, relative to each vertex in the selected feature.
Use the option to Specify the Base Height to use at Each Vertex to manually set the heights for each vertex in the selected feature. Specify if the Base Heights in the vertex list are above ground or above sea level values. This option is disabled of multiple area features are selected. If multiple line features are selected the line with the most vertices will have the elevations reported and subsequent lines with fewer vertices will use the needed number of elevation values from the vertex list.
Interpolate to Fill Small Gaps in Data - This check box option will fill any small areas of missing data by interpolating surrounding valid data using an IDW method. This is useful for filling small gaps between adjacent tiles or small holes in elevation data.
Pile Volume(s) will calculate the volume of a pile as defined by an area feature by creating sample elevations along the perimeter of the selected area feature to form the 'base' surface. The elevation values for each sample will be where the elevation value from where the sample point intersects with the loaded elevation model.
The sample spacing is determined by the width of the area feature and the height of the pile. It will be 1/200th of the width of the selected area feature, or 1/200th of the height of the pile - whichever is the smallest interval. For example, a pile that is 50m width by 40m tall will have its boundary resampled at 0.2m spacing (40m/200m = 0.2m).
To use the Pile Volume measurement tool, you will need an area feature that encompasses the hill or pile you would like to measure the volume of, or you will need to digitize a new area feature around the pile. The area feature does not need to have elevations defined for vertices, as the elevation values to calculate the Pile Volume will be derived from the generated samples.
The Measure Volume Between Surfaces command allows the user to calculate the volume between 2 terrain surfaces. When selected, the command displays a dialog allowing you to select the 2 layers to calculate the volume between as well as the region within which to do the volume calculation.
Both the Measure Volume Between Surfaces and the Pile Volume volumetric calculations work by dividing the area of interest up in to small rectangular pieces, and then calculating the sum volume of the small 3D rectangles between the two terrain models or the terrain model and the cut surface (Pile Volumes).
Pile Volume(s) will calculate the volume within a defined area relative to how the all of the vertices of a selected area feature meet the terrain surface or elevation model. Vertices that do not meet the terrain surface are omitted from the calculation.
To use the Pile Volume measurement tool, you will need an area feature that encompasses the hill or pile you would like to measure the volume of, or you will need to digitize a new area feature around the pile. If the area feature does not contain elevation values for the vertices, you will need to add these. For a more accurate measurement, make sure the area feature encloses the pile or hill, without having a lot of space around the perimeter.
The calculation will use the entered height in meters as the base height for all vertices in the selected area. Terrain above this height will contribute to cut volume, terrain below this height will contribute to fill volume.
1.Does we need GCP foe more accurate volume determination ? and Normal geottaged images in geographical cooradinates is enough for reliable results between 90-95% of accuracy which gives better result ?
If geotagged images are used and the volume measurements are supposed to be computed for small areas, GCPs are not required for accurate volume measurements. However, if volumes have to be calculated for large areas, GCPs are required for accurate measurements.
When calculating the volumes, the vertices of a base have to be marked in at least two images in order to calculate the error. Additionally, it is important to select the right settings for the base that fit your purpose. Step by step instructions how to draw a volume can be found in the following article 202560319 and description of settings can be found here 208652926.
If the same base is used in both Pix4Dmapper and Global Mapper for volume measurement, the difference in values should be minor. It is possible to export the base from Pix4Dmapper which can be imported to Global Mapper. For more information: 211245943.
The DJI camera has the rolling shutter that can be an issue for the reconstruction depending on the flight conditions ( low height of the flight, high speed of the drone ) and the area that is mapped. My go-to solution in these cases would be to:
Hi Charanya, including GCPs in a project does not depend on the area, GCPs are welcome if you want accuracy in the project no matter what the size is. What is the accuracy of the GPS you have? If your volume calculation area is small, then the error due to not having GCPs will be lower, if the volume area is more, the error will accumulate.
To zoom in on a specific point, choose the [Zoom tool] from the toolbar or, [Tool/Zoom] from menu bar. A magnifying glass icon should appear on the screen. To zoom in, left click without dragging the mouse. The view is centered on where the mouse was clicked and will zoom in by a factor of two. To zoom out, right click without dragging the mouse. The view will zoom out by a factor of two, centered on where the mouse was clicked. You can also hold down the Ctrl key while right clicking to restore the view to the last zoomed view.
To change the center point of the image without changing the magnification, depress the left mouse button, drag the view to the desired location, then release the left mouse button to redraw the view at the new location.
If you just want to recenter on a new location without dragging, just click the left mouse button at the new desired location and the view will be recentered on that location (this provides the functionality of the old Recenter Tool).
You can also save a measurement to a separate feature by right clicking and selecting "Save Measurement" from the list that pops up. You can then export these measurements to new vector files, such as Shapefiles or DXF, or modify them with the Digitizer Tool. There is also an option to copy the measurement text to the clipboard when you right-click.
If you have gridded elevation data loaded under the measurement, you can also calculate the Cut-and-Fill volume either within the measurement area or within some distance of the measurement line. To do this, simply right click then select the "Measure Volume (Cut-and-Fill)" option that appears. Selecting this option will display the Setup Volume Calculation Parameters dialog (pictured below), which allows you to set up the volume measurement.
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