Cut Fill Elevation Comparison

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The new cut fill comparison tool set allows you to quickly compare the elevation of one map to another map or to a design surface (grading plan). With heatmap visualization, you can easily identify where soils have been cut or filled from one map to another or how much soils need to be cut or filled to reach design grade so that you can track changes and monitor progress of earthmoving. With volume measurement comparison, you can quantify the amount of earth moved -- either for an entire site or for an individual volume measurement, like a pit or stockpile -- so that you can verify subcontractor work, manage stockpile inventory and better keep to a project schedule.

How to Visualize Cut and Fill

You will see a new layer available in your projects called “Cut/Fill”. When you select the layer, a red/blue heatmap layer will appear on top of the map you are viewing which shows the elevation difference between that map and another map within the project.

This is calculated by taking the elevation values from the map you are viewing and subtracting the elevation values from the comparison map.

Viewed Map Elevations - Comparison Map Elevations = Cut/Fill Visualization

Cut will appear in red, and fill will appear in blue. The greater the difference in elevation between the two maps, the greater the intensity of the red or blue color. What is considered "cut" and what is considered "fill" will depend upon whether you are comparing your map to a previous map or to a future map or design plan.

When comparing to a previous map, areas that have been excavated from the previous date to the viewed map will be labeled "cut", indicating that earth has been "cut away", and areas where the elevation has become higher will be labeled "fill", indicating where soils have been "filled in".

When comparing to a design plan or later map, cut and fill are expressed in terms of what would need to be cut or filled to match the later state or design plan. You can think of this as "proposed cut" and "proposed fill". For example, areas where my map is higher than the design plan would be colored red for "cut", meaning that earth would need to be "cut away" to reach design elevations.

Some sites may involve enormous amounts of earthmoving, changing grades by 50 feet or more, while others may only involve grading changes of a few feet. You can adjust the cut/fill layer to focus on the range of elevation change that matters to you. This is the minimum and maximum values beyond which cut and fill will appear as either solid blue or solid red. If your site has only small grading changes, you will want to decrease the visualization range. If your site has very large grading changes, you will want to increase the visualization range.

Comparing the Elevation of Two Maps

By default, the heatmap will show the elevation comparison between the map you are viewing and the previous map within the project, but if you would like to compare to a different map, you can select a different one from the Cut/Fill details page.

Compare Digital Surface Models or Digital Terrain Models

When you view the Cut/Fill layer, you have the option to compare either the Digital Surface Models from two maps or the Digital Terrain Models. Comparing the Digital Surface Models can be useful to detect differences structures, equipment or vegetation from map to map. Comparing Digital Terrain Models is more useful for visualizing changes in terrain due to earthmoving.

Compare Map Elevations to Design Surface (Grading Plan)

Upload the design surface of the final elevations for your project once, and then compare against each drone map to see how much earth still needs to be moved. Just click the "Add" button next to "Project Files" and select "Design Surface". Then upload your design surface as an Elevation GeoTIFF.

How to export an Elevation GeoTIFF

Here's a support doc explaining how to export this file type from Civil 3D. Make sure when exporting that the tiff is geo-referenced with a coordinate system. Otherwise, we will be unable to process it and align it to your maps in DroneDeploy.

Your design surface will take about 10-20 minutes to process. Once processing is complete, you will be able to view it as an elevation layer in DroneDeploy.

You will also be able to select the design file for comparison from the Cut/Fill layer and from within volume annotations.

How to Quantify Cut/Fill Using Volume Comparison

When you view the Cut/Fill details, you will see the total volume difference expressed as Total Cut, Total Fill, and Net Total Volume between the two maps you are comparing within the area where they overlap.

However, the area of overlap may include more than the area of earthmoving that you want to track. To measure the volume difference between two maps within a specific area, you can use the volume measurement tool. Just define the perimeter of the area you want to measure and then select a Comparison Map as a base plane. You can turn on the Cut/Fill visualization layer while you are making your volume measurement to help you see where the elevation is different between the two maps.

Here's an example of an area of excavation on two different days. When you compare the drone maps and elevation models from each date, you can see that more of the area has been excavated by the second date.

The cut/fill visualization can enable you to visualize the change in just one view, without having to toggle back and forth between different maps dates, and with the elevation comparison, you can calculate that over 1,420 cubic yards have been excavated in that area between February 4th and February 25.

Troubleshooting Tips

With default drone map processing, elevations from map to map can vary based upon the GPS error of the drone and variations in barometric pressure. This means that the elevation of a point that has not moved may have different elevations on different maps of that point -- and this in turn is a problem for Cut/Fill visualization and volume comparison measurements, which use those elevation values.

If, for example, all of the elevations in your map are few feet higher than the elevations in your map from Monday, your entire cut/fill map would appear Red -- not because that much soil has been added but because of the GPS variation from the drone.

Map processing in DroneDeploy will attempt to correct these issues and align each processed map to previous maps in the same location, however, especially when comparing maps processed before DroneDeploy began automatically aligning maps at the end of 2018, you may still see significant elevation variations between maps.

Fortunately, there are two ways that you can address these variations. For maps that have already been processed, you can manually correct elevations by using Elevation Calibration to enter the same known elevation at the same point on the different maps that you want to compare. For example, if you know that the corner of the sidewalk is 51.3 ft above sea level, you can enter the elevation at that point on each of the maps you want to compare.

Another option is to use Ground Control Points when processing your maps. Especially if you need a high degree of accuracy for your cut/fill measurements across a large site, we strongly recommend using Ground Control Points to increase the accuracy of your maps and your volume comparisons.

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Updated 8 months ago

Cut Fill Elevation Comparison

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