Step 1: Marking Control Points - Slab on Grade/Void – Self-Capture

1 Introduction

Siteaware's Digital Construction Verification system relies on the dispersion of accurately measured ground control points (GCPs) for timely and accurate verification results. The two factors that affect the quality of the scan are 1) The dispersion of the GCPs to cover the entire scan area and 2) The accuracy of the measurements themselves. This section provides guidelines for placing and measuring GCPs, to ensure you receive consistent results every time you scan.

2 GCP Layout Rules of Thumb

2.1 Placement Locations

To achieve the highest level of accuracy in all areas of the pour deck, it is required to place CPs throughout the deck as each point provides a high level of accuracy for its surrounding area. At least five (5) control points (Siteaware recommends placing 6-8) per pour area should be placed. The ideal CP layout for a typical pour area will have one (1) CP in the vicinity of the four (4) corners of the deck and an additional CP in the center (See Image 1). However, not every pour will be rectangular and therefore it is important to follow the following guidelines to achieve the most accurate results:

A CP should be placed close to every corner of the pour area to maximize coverage. (See Image 2 for an L -shaped deck.)
If the pour area is wide but narrow (see Image 3) place the CPs staggered as shown.

Siteaware will also supply a recommended layout (see below) for every pour area which can be followed directly to achieve the best results.

3 GCP Placement Method

Siteaware recommends that the GCPs be placed while the surveyor is laying out control for the other trades. This eliminates the need for the surveyor to re-establish a base point and ensures that the deck is nearly empty of construction materials, providing the most flexible layout which will lead to more accurate results.

3.1 GCP Best Practices

Once placed and measured, it is critical that the GCPs are not moved. Any movement, even if slight, can decrease the accuracy of the digital twin and subsequent scan results. To avoid such scenarios, please ensure that the GCPs are not placed in areas where elements such as sleeves or embeds will need to be placed or in locations with dense rebar or PT Tendon layouts.

Tip: To prevent any issues with the visibility or movement of the GCPs, it's a good idea to pre-plan their location using the field-use documentation. This will help avoid clashes with the installation and ensure a smooth GCP layout process.

If GCPs are moved after they have been measured they must be remeasured.

3.2 How to place a GCP

For scans of the slab on grade pours where a vapor barrier is being used, the GCPs may need to be placed twice. Siteaware recommends performing the first scan before the placement of the vapor barrier to allow for the easy adjustment of any penetrations or grade beams should there be any corrections required. Once the vapor barrier is placed these GCPs will be covered and a new set of stickers will need to be placed.

Additionally, as the stickers are not intended to be placed on dirt, the pre-vapor GCPs should be placed on a metal plate that can be fixed to the ground to ensure they won't be moved during the scan.

GCP on a Plate on Grade:

Siteaware will provide the plates as part of the Self-capture kit

GCP on the Vapor Barrier

4 Record the Data

Once the sticker placement and measurement are complete, measure their locations with a Total Station and upload the file of coordinates to Siteaware via the Self Capture Upload Portal.

Reminder: The column sequence is critical, please share the coordinates as Easting, Northing, and Elevation

4.1 Upload the Coordinates

After the stickers have been measured, upload the file containing their coordinates to the Self-Capture Upload Portal.

5. Placing GCPs on Anchor Bolts

If anchor bolts have already been installed, GCP stickers can be placed on anchor bolts instead of being placed on grade. The advantage to this method is that Siteaware will pre-provide possible sticker placement locations such that no coordinates need to be surveyed or uploaded.

5.1 Timing

A CP sticker should be placed on one anchor bolt at each column noted as close to the time of the scan as possible to ensure they are not disturbed before the scan.

5.2 Layout

For every pour area, Siteaware will provide a map detailing the recommended columns that should be marked as a control point. Each anchor bolt will receive a naming convention similar to the one shown on the right and the naming convention of the control should be [Column Name] [Anchor Bolt] (Ex. for anchor bolt G of the column at the intersection of Col Line A and Col Line 1 the name would be A1G).

5.3 Uploading Control Points

As the locations of the controls are pre-determined, there is no need to upload any coordinate data.

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