Laci Dru Street Replacement

Cost, quality and lead time. These three items are possibly the most critical factors that will define the success of your company. While there are many ways to affect these factors, properly utilizing technology can be one of the quickest means.

On a recent street replacement project, AeroView Services used UAV aerial mapping and GPS machine control to give our client a competitive advantage over their competition.

Originally, the Laci Dru project consisted of just extending the street, but soon after the extension project started, the City Engineer determined that the existing block of Laci Dru Street needed to be replaced as well. As the project was a simple remove and replace, without any grade changes, the contractor's change order was accepted with the condition that it would be started almost immediately.

To meet the City Engineer's tight deadline, work needed to start within 48 hours, but the contractor did not have the personnel available to place offset stakes or survey the street with RTK GPS.

Satellite Imagery of Laci Dru

That's when the City Engineer approved the use of UAV technology for the project, and the client hired AeroView Services to first map the site with a UAV and then based off that data, create a machine control file that could be plugged directly into the earth moving equipment being utilized to replace the road.

AeroView's first step in the process was setting control for the site and mapping it with our DJI Matrice 600 hexacopter. Setting control is a critical step for achieving accurate results. Please read our article on ground control to learn more. After placing control, we programmed a flight pattern for the UAV, setting up parameters such as flight speed, front overlap, side overlap, etc. The actual flight time for the site was 20 minutes with approximately 300 photos taken (see UAV photo below)

The second step, after flying the site, was to process the data and create a colorized point cloud along with an orthophoto, both of which increase accuracy and aid and speed the design process.

Producing Point Clouds and Orthophotos

The point cloud is produced with photogrammetry, which utilizes the perspective of the photos and creates a 3D model. The point cloud for Laci Dru Street had more than 25,000,000 points of data, with each point of data having a X,Y,Z coordinate (northing, easting, elevation) associated with it, just like a traditional RTK GPS topo survey.

The orthophoto is made by stitching all of the photos together and geometrically removing the perspective from the individual photos, creating a geometrically accurate photo. Accurate measurements for area and distance can be taken from orthophotos of critical importance for the contractor to accurately create a bill of materials for the project.

The point cloud and orthophoto are the two primary data sets which are used map the bare earth surface model of the site, which will then be used as the basis for later design and machine control creation (see raw, unedited point cloud below). To create a bare earth surface, all non-ground points need to be removed from the point cloud, such as cars, trees, houses, etc.

While the benefits of the point cloud are obvious, the orthophoto likewise has many uses. While everyone likes a high resolution photograph of their job site, an orthophoto has multiple other benefits. It provides engineers with a detailed view of existing features on the site, such as inlets, manholes, curbs, etc., to be referenced during the design process. Contractors also use the orthophoto to monitor and verify jobsite progress for payment, perform material takeoffs, and optimize site management. These elements can be easily located with UAV imagery, but are not seen clearly, or measured accurately, with satellite imagery.

Also, the orthophoto, can be loaded into CAD software and used as a visual aid and supplement for the design process (see a side-by-side comparison of UAV imagery and satellite imagery below). As can be seen, the UAV imagery gives much more information and clarity.

Once the point cloud has been scrubbed of all non-ground points, what is left is a point cloud with over 15,000,000 points of data representing the earths surface, accurate within 0.06' horizontally and 0.1' vertically, as compared to RTK GPS checkshots.

Next, a 3D surface can be fit to the point cloud. This surface can be loaded into any CAD software and used as the basis for future designs and analysis. AeroView Services has the ability and expertise to create 3D surfaces in any format and size that is requested by our clients, allowing them to operate within their typical workflow, thus avoiding a steep learning curve and training cost (see 3D surface below).

In addition, contour maps can be created from the surface and overlayed on the UAV orthophoto (see the contour map with 1' intervals, right).

Creating 3D Model for Machine Control

Since the scope of the project was to replace it, not change any features on the road, the next step was to use our UAV data to a create machine control model the client could directly load into their earth moving equipment. All machine control files were created by Quantum Land Design, which is the parent company of AeroView Services. In this case, the 3D model was loaded directly into the contractor's grading equipment through the Trimble Connected Community.

The contour lines of the machine control file represents the proposed surface, or the future state of the site (see contour lines of the machine control file overlayed on the UAV orthophoto below). By utilizing GPS machine control, our client is able to complete the work in a fraction of the time and with a significantly reduced labor cost and zero rework. The contractor estimated that eliminating offset stakes and the associated work to set grade saved them at least 16 hours of labor (2 employees x 8 hours)

The Laci Dru replacement project show how utilizing new technology gave a company a quantum leap in capability.

Efficient: AeroView Services was able to come on site, map the area and deliver a machine control file to the client in less than 48 hours.
Accurate: According the City Engineer, with the amount and accuracy of the data collected, the quality of the work performed by the client was better than if performed by traditional methods.
Cost Effective: By utilizing UAV aerial mapping and GPS machine control, our client was able to reduce labor costs significantly, allowing them to be more profitable and increase their capacity.

By utilizing AeroView Services and our state of the art technology, the client delivered a quality product, which was completed on-time and under budget.

Laci Dru Street Replacement

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