Creating a Civil 3D surface from an Esri ASCII raster

Digital terrain models, such as LiDAR data, are frequently stored in Esri ASCII raster files (*.asc). In this blog, we'll explain the structure of the data in this file type and walk through the workflow of creating an ASC file into a Civil 3D surface.

An esri ASCII raster file holds the elevation of several square cells that make up a grid in the context of digital terrain models. You may see the data that makes up the file if you open it in a text editor like notepad. It starts with a header that defines the properties of the grid followed by the data, with the grid cells elevations separated by spaces.

A list of parameters that are part of the header are listed below:

·         ncols: number of cell columns.

·         nrows: number of cell rows.

·         xllcorner or xllcenter: x coordinate of the lower left corner (or centre) of the origin cell, located in the lower left corner of the grid.

·         yllcorner or yllcenter: y coordinate of the lower left corner (or centre) of the origin cell, located in the lower left corner of the grid.

·         cellsize: size of each of the square cells.

·     NODATA_value: value that designates that no data exists for a particular cell. This parameter is optional and may not exist.

The data that follows is a list of elevations, listed from top to bottom and left to right, divided by spaces.  In other words, the elevation of the upper left cell is the first value, followed by the elevation of the second leftmost cell from the top row etc. The values are typically organised into separate lines that correspond to the various rows, with the first line representing the row at the top of the raster. The number of columns determines when the next row starts, so carriage returns are not required at the end of each row.

Raster grid

The two examples below show the same raster grid, using the coordinates of the corner or the centre of the origin cell.

Checking coordinate systems

We must ensure that the coordinate system is set correctly, before creating a surface from an ASC file in Civil 3D. It can be set from ‘Edit Drawing Settings…’, as shown below.

Creating a new surface

We then begin by creating a new surface.

For points that lie in a regular grid, it is advised to use a grid surface rather than a TIN or triangulation surface. A grid surface will load more quickly than a TIN surface since it uses less disc space, especially if the number of points is high.

Grid X-spacing and grid Y-spacing should be set to the ‘cellsize’ parameter from the header of the ASC file.

Adding a DEM file

From prospector, look for the surface and add the DEM file from the ‘Definition’ branch.

Browse to the ASC file and set ‘Use custom null elevation’ to ‘Yes’ if the ‘NODATA_value’ parameter is part of the header in the ASC file. In that case, ‘Null elevation’ should be set to the ‘NODATA_value’ parameter. If that number is found in the file, it will be ignored, and no point will be created for that particular grid cell. If you don’t use a custom null elevation, it will create a point at that level (-9999m in our example), which is incorrect.

Civil 3D Surface

After confirming the previous dialog, the surface will be generated.

A point will be created at the centre of each grid cell. In the picture below, the grid from the ASC file is shown in cyan, the boundary of the surface in red, and the surface triangles in white. The coordinates and levels that have been labelled can be found in the example files that we showed at the start of the blog.

If you would like to learn more about Civil 3D, please visit our product page. Alternatively, you can contact SYMETRI on 0345 370 1444 or email us at info@symetri.co.uk.

Utilising the Autodesk Construction Cloud to improve the preconstruction phase

 

“Autodesk Construction Cloud is helping us to improve design management processes and model coordination. We have seen improvements in productivity, outcomes and helping our teams to handle further capacity”

Lee Ramsey, Digital Director for Morgan Sindall Construction

Morgan Sindall Construction is a UK business with a network of local offices. Project capabilities cover the entire range of construction activities, from special works and repair and maintenance, to major landmark schemes delivered as standalone projects or as part of larger multiple project frameworks. The company works across both the public and private sectors to deliver the social infrastructure around us – from schools, universities and hospitals to retail, office, and leisure environments.

Morgan Sindall Construction is a component of the Morgan Sindall Group plc, with annual revenues of £3.2 billion and six operating divisions, including Construction & Infrastructure, Fit Out, Property Services, Partnership Housing, Urban Regeneration, and Investments. 

 

Automating traditional processes

Each of Morgan Sindall Construction's projects is centred on sustainability and efficiency, and to achieve their goals of becoming the most coveted and sustainable company in the industry, they had to match their business goals with the requirements and expectations of their workforce, clients, supply chain partners, and other stakeholders. This involves ensuring that their projects are 100% safe, finished on time, and of high quality.

Morgan Sindall Construction align their strategy to the UK's Digital Construction goals. Since the UK Government Construction Strategy was published in 2016, various digital projects have been delivered thanks to their commitment to Digital Construction, which is supported by their business philosophy of Perfect Delivery. These projects have connected people, process, and technology, improved consistency, enhanced decision-making, and decreased risk at the design, construction, and operation stages of their projects.

Improving design management and model coordination

Complementing this strategy is their recent implementation of Autodesk Construction Cloud (ACC), a portfolio of construction management software products supporting workflows across all phases of construction—from design, to planning, to building, to operations.

“Management of design is complex, involving multiple stakeholder interests, external approvals and consents, but it’s very important to us as a contractor. It is during the design and preconstruction phase where the DNA of the project will be confirmed, which is fundamental to our success in winning work and delivery. Reduction of time is also critical during the preconstruction phase so that we can reduce our internal staff costs and design team fees, which is one of the key items in the UK Government construction strategy,” says Lee.

Find out how Autodesk Construction Cloud (ACC) is helping with this process below

Challenges

• Clash detection process could take up to 3 weeks.
• Review processes taking too long.
• Too many errors being produced on 2D outputs.
• Synchronisation of models and uploading and downloading of models.
• Team accountability.

Solutions

• Autodesk Construction Cloud provides automated detecting and grouping of clashes in minutes.
• It allows all parties to see the design as it develops in almost real time which has reduced abortive design work.
• The model comparison tool has allowed the design team to see a 50% time saving in the identification of change as everything is made visible.
• The change analysis feature helps reduce risk on projects.

 

Benefits

·     Synchronisation of models and uploading and downloading of models time has reduced by 78%. This benefit significantly reduced the impact of Covid-19 and enabled Morgan Sindall Construction’s teams to work remotely, yet still collaborate.

• Time taken to review information has reduced, resulting in a 20% reduction in the preconstruction phase.
• The team have been taking ownership for their own information before being issued to others and the quality of the output has increased due to the transparency.
• The identification of changes and issues has significantly improved resulting in a 62% time saving as people have been resolving and controlling their own work.
• 20% improvement in time taken to update model to co-ordinate with other disciplines.
• The design team meeting time has been reduced by 67% as there has been a lot less comments when reviewing the 2D outputs and issues are being addressed at source in the 3D model.
• The traditional clash detection process was taking 3 weeks. With Autodesk Construction Cloud, it is now taking minutes.

 

Learn more about Morgan Sindall Construction: www.morgansindallconstruction.com/

 

Would you like to improve your construction workflow with Autodesk Construction Cloud? Please get in touch with us at SYMETRI by emailing us at info@symetri.co.uk or call us on 0345 370 1444.