How to Calculate Slope with RTK GNSS: Step-by-Step Guide
To calculate slope with an RTK GNSS receiver, collect two points using Point Survey in ApekSurv — one at the top of the slope (Point A) and one at the bottom (Point B). Navigate to Tools → Coordinate Inverse Calculation, import both points, and tap Calculate. ApekSurv instantly returns the azimuth, elevation difference, and slope percentage between the two measured locations.
When to Use RTK for Slope Calculation
Determining terrain grade is an essential element in grade stakeouts, drainage modeling, and structural excavations. Utilizing an RTK GNSS receiver for calculation optimizes field accuracy during road construction slope acceptance, earthwork volume verification, agricultural terracing layouts, and drainage channel engineering validation. Evaluating slopes instantly in the field ensures compliance with design specs prior to machine deployment.
Traditional grading calculations relying on optical auto-levels and manual tape measures are highly susceptible to parallax errors and typically require a two-person crew to pull lines over uneven surfaces. Upgrading to an RTK workflow eliminates physical tape baselines, allowing a single surveyor to capture precise three-dimensional coordinate vectors across hundreds of meters in seconds. This transformation cuts field runtime drastically while retaining sub-centimeter elevation tracking.
What You Need
Ensure your field configuration includes the following mandatory equipment and software modules before calculating terrain slope vectors:
- APEKS RTK GNSS Receiver: Set to Rover mode and actively linked to a localized NTRIP CORS network or field base station.
- Android Field Controller: Loaded with the latest version of the ApekSurv field software application.
- Confirmed Fixed Solution: Ensure full RTK initialization and initialization lock are achieved before logging any 3D points.
- Two Accessible Locations: Clear physical access to both the crest (top) and toe (bottom) of the target slope area.
Walk to the highest elevation point of the target slope profile. Plumb the survey pole directly over the chosen location, open your ApekSurv controller interface, and navigate into the Point Survey screen. Confirm that your solution status is firmly locked on Fixed, then trigger the measurement and save the file, assigning it a clear label such as Point A or Pt2.
Carefully descend to the lower grade break or toe of the slope structure. Rest the pole shoe firmly on the measurement point, level the circular vial bubble, and utilize the Point Survey interface to record the lower coordinate, saving it as Point B or Pt1.
Exit the primary mapping workspace and return to the application's central dashboard. Select the Tools menu layer, then look for and click on the Coordinate Inverse Calculation function. This integrated mathematical processor calculates geometric relationships—including spatial distances, azimuth bearings, total elevation drops, and true grade slopes—directly from raw 3D grid values.
Tap into the designated Point A configuration line and select your stored top-of-slope coordinate node from the internal database. Next, tap into the Point B parameter entry slot and load your lower bottom-of-slope coordinate point. With both point registers populated, press the Calculate button to run the algorithm.
The ApekSurv calculation engine immediately processes the values and displays three vital engineering data lines on screen: Azimuth (the directional compass heading connecting the two markers), Elevation Difference (the net vertical drop measured in linear meters), and Slope (the resulting grade expressed as a percentage value, matching the 25.54% example verified during live operations). The processing logic derives this percentage by dividing the true elevation drop by the true horizontal distance, then scaling by 100%.
Practical Applications
Utilizing the integrated coordinate inverse calculation features within ApekSurv provides distinct tactical advantages across multiple industrial field operations:
- Road construction: Instantly check cross-slope embankments, structural subgrades, and cut/fill slope ratios relative to design criteria to prevent drainage errors.
- Agricultural terracing: Map and monitor topography before planting cycles to establish optimized irrigation contours and manage rainwater runoff velocity.
- Drainage channel design: Verify that wastewater path gradients and drainage ditches maintain the minimum slopes required to ensure gravity-fed flow.
- Earthworks QA: Gather fast, highly accurate as-built grade documentation across completed slopes to generate validation reports for project handover.
Frequently Asked Questions
Can I calculate slope between two points that are far apart?
Yes. The coordinate inverse calculation engine inside ApekSurv computes mathematical vectors between any two stored points in your active database, regardless of baseline distance. However, keep in mind that for extremely long distances, the result reflects the average composite slope over that span, rather than localized grade variations.
What is the difference between slope percentage and slope angle?
Slope percentage represents the vertical rise divided by the horizontal run multiplied by 100 (e.g., a 1-meter drop over 4 horizontal meters equals a 25% slope). Slope angle measures the angular inclination relative to a flat horizontal plane in degrees. ApekSurv natively delivers the grade output in an industry-standard percentage format.
Does this method work without a CORS network?
Yes. While a network CORS infrastructure is ideal for single-rover setups, you can execute this workflow using a standard local Base and Rover pairing. The core requirement is maintaining a stable RTK Fixed status across both points to keep your elevation precision within sub-centimeter parameters.
Can I save the slope calculation result in ApekSurv?
Yes. After running the calculation, you can save the resulting data report or export the inverse calculation log directly within the ApekSurv file directory. This allows you to archive the azimuth, elevation difference, and grade metrics for subsequent quality assurance documentation.