5. Surveying

Surveying Overview
The 'Collect' wizard page
Field Surveying
Magic Plane
Drain Surveying
Boundary Survey
Survey Guidelines
Surveying Tips and FAQ
Surveying with extra sensors (T3RRA Survey only)
Map: Recent GPS Errors

Surveying Overview

The ‘Collection’ wizard step allows you to collect elevation heights from your field. This is done to create a topographic representation of the field surface.

In T3RRA software collection is normally accomplished by driving over the surface of a field while logging GPS elevations. Once sufficient points have been collected (surveyed) they are then processed in order to create a Digital Elevation Model (see definitions). In T3RRA software we refer to this process as ‘Surfacing’ and this is performed in the next wizard step.

The key concept with surveying is: “Collect enough points to create a good surface, but no more”.

If you do not collect enough points from the field you will end up with a poor representation of the field. If you collect too many points you will have wasted time and fuel in order to create a surface that is not markedly better than one created from fewer points. As well as the number of points collected, the accuracy of the final surface depends on where the points are collected.

Getting a good representation of the field surface is not a difficult task. Getting a good surface representation while minimizing time spent doing it requires more effort and experience. Figuring out the total number of points to collect, and the best pattern to collect them in, is an art that requires experience. If you do a lot of it you will soon start to understand how to improve and optimize your surveying technique.

However, new and casual users need not despair. In general, we would advise users not to attempt to optimize this activity too much. Extra time spent getting a good survey is usually insignificant relative to the time spent moving dirt. A thorough survey and an appropriate design will save far more dirt moving time than any time added while over-surveying.

Also, be sure to read the section ‘Surveying tips’ later in this document.

The 'Collect' wizard page

If you are at the Main Page and want to begin surveying first press the 'Wizard' button.

Then choose the second wizard step ‘Collect’ at the bottom of the page. This will take you to the ‘Collect’ wizard page.

You are able to import survey data from other sources as CSV for Field and Drain surveys or as KML for Boundary Surveys. Press the 'Import' button to import existing survey data in CSV format.

Hint: If you would like to examine the CSV format used by T3RRA software to import/export survey points, simply export some collected data and open the resulting file in a text editor.

To begin collecting elevation points use the ‘Start’ button (in the centre section of the screen). If data has previously been collected this will still be present when you enter the mapping screen.

We consider it best practice to drop a marker for reference prior to beginning any survey. Do this at a location you know you can return to reliably. This will assist you in shifting the survey points in the future should it become necessary to do so.

Before collecting elevation points you must decide whether you are collecting data for a full field, for a drain or a boundary. We distinguish between these three collections because the way the data is processed in subsequent steps is quite different. You can however collect drains, full field and boundary surface points at the same time by swapping between them as required. Survey modes are swapped between by pressing the survey button in the bottom right of the screen until the icon for the type of surveying you wish to do is displayed or until the text in the top left corner of the screen reads as the type of surveying you would like to do.

NOTE: Best practice is to not overlap different survey types. Instead, press Pause when traveling over different survey points then Resume once clear.

(the icons below: Field survey on left, Drain survey in center, Boundary survey on right)

To begin collection select the ‘Start’ button.

The ‘Pause’ button is used to finish data collection while moving around obstacles or avoiding replication of survey points, while the ‘Stop‘ button is used when data collection is finished.

You can edit your survey data at this point. For more information, see “Survey point edit controls”. These options are documented under the collection page, and operate the same way.

When all collection and editing of data points is complete use the 'Return' button to return to the main ‘Collect’ wizard page. You will be asked to confirm keeping changes to the elevation data.

At this point it is recommended that you save your project. If you wish to save the file externally use 'Export' step of the wizard found at the bottom of the screen. Field and Drain Surveys data will be exported as CSV files, Boundary survey data will be exported as KML files

NOTE: You should always use ‘Save proj.’ to save your T3RRA project. This saves in the native file format and is the easiest file type to reopen in T3RRA software. Exporting is optional, and depending on the type of export you perform you may not always be saving all the information that exists with your T3RRA software project.

Field Surveying

When you enter surveying you will be in Field surveying mode (except in T3RRA Ditch where Drain survey mode is the default). Points that are collected in field survey mode are shown on the map as circles.

We do not require you to collect a field boundary when surveying. Some do consider it best practice to drive the perimeter of a field regardless, collecting elevation points as they go.

When surveying fields travel slowly across the field to ensure that plenty of data is recorded for an accurate representation in later stages.

Collected points can be deleted using the two available methods:

Delete in a circle.
Delete points in line.

Markers can also be placed and deleted.

Magic Plane

The Magic plane is a shortcut method for creating a plane of survey points without actually having to collect them. This can be used when the grade and direction of the desired plane is known and getting accurate cut/fill volumes is not required. An example would be a building pad.

NOTE: If you use ‘Magic plane’ as your original surface you are unlikely to be able to create an accurate cut/fill map. This is because the newly created plane is unlikely to match the actual real world surface. Any cut/fill map created from a design you place on a ‘Magic plane’ will be relative to it, and not the real world surface.

Start Point - The 2 options available are center or edge, this will generate the magic plane with your current location (or the location of some pre-existing surveyed points) at the center, or at the center of an edge.

Field Length - This is the length of the magic plane and can be adjusted as needed.

Field Width - This is the width of the magic plane and can also be adjusted as needed.

Direction - This sets which direction the magic plane is oriented.

Slope Percentage - This sets the degree of the slope.

Secondary slope - This is enabled by selecting the “Enable secondary slope” check box. (the secondary slope runs at 90o to the primary)

Drain Surveying

T3RRA has a drain collection mode that you must use when surveying drain lines. The button is at the bottom right of the survey collection map window.

When in 'Drain survey' mode you must drive the length of the drain in order to collect the data. It doesn’t matter whether you drive from source to outlet or vice versa. When points are collected in 'Drain survey' mode the data points are displayed as squares.

Available features:

Delete all or portion of drain line.
Extend drain’s length.
Split drains.

(see Drain specific edit controls)

After you have finished surveying:

Design drains from either direction.
Choose Best-Fit, Multi-Fit, or Linear-Fit drain design.
Add batters/backslopes to drains.
Export drains as guidance curves.

Boundary Survey

Boundary surveying allows you to survey the outer perimeter of a field which can be used for Design purposes.

In T3RRA software the boundary survey mode is located in the bottom right corner of the survey screen and is accessed by pressing the survey mode button until the boundary survey mode icon is displayed and ‘Boundary’ is displayed in the top left corner of the screen.

When using Boundary survey it is not required to survey the entire perimeter of the field. If you start your system in one corner of your field but you know the position you want to start from is directly across from you, you can survey the rest of the sides of the field and the Boundary survey tools will automatically close the boundary line once you press the stop collection button.

To make a boundary with few points (as shown above), simply start collecting a boundary while stationary, then pause collection while traveling to the next corner. Once at the next corner, resume collection for a few seconds, then pause to go to the next corner. In this way you can collect a boundary with only the points you want, but you can use the delete points tools to thin out extraneous points as necessary afterwards.

There are 2 tools specific to only Boundaries: Delete boundary, and Scale the boundary.

Delete boundary: allows you to delete a specific boundary if multiple have been recorded or if you wish to start the surveying over again. Elevation points that are collected while recording the boundary will remain even after the boundary has been deleted.

Scale the Boundary: this tool allows you to expand or retract the size of the boundary lines by moving each boundary line a set distance away from the original position to a maximum of 98ft (30m) and a minimum of -98ft (-30m).

Exporting boundary information: Boundary survey information can be exported as Shapefiles or as KML files

Survey Guidelines

No matter what type of surveying you are doing you are able to implement guidance lines on the survey surface by pressing the guideline button at the top of the screen.

The 'Guidance' button will cause a pop-up window to appear on the screen with a two design options for AB lines in the 'Type' dropdown menu.

The default type is 'point A + Point B' which draws AB lines based on 2 set points on the field. The location of these points can be set in 3 different ways

If you know the latitude and longitude for the points they can be input manually.
Drive to Point A and click “Set” then drive to Point B and click “Set”.
If you have recorded markers you are able to use their GPS locations for either or both of the points.

A single point can be used by selecting the 'Point A + Heading' type. Like with using 2 set points Point A can be set using the same methods mentioned above. The 2nd point is replaced with your current heading and can be adjusted to a heading of your choice.

Once the 'Type' is selected the guidelines will then create a central line from the information provided and duplicate lines parallel to it, spacing the to what has been set in the ‘Track spacing’ field at the bottom of the pop-up window.

The lines made with the guidance tool will be blue and the centre line will be red.

The nearest line to your current location will be highlighted bright purple.

As shown below when surveying a light bar at the top of the screen will display how far you are from the nearest line, which side of the line you are on, and which line you are on (e.g. E2 is 2nd line east of the centre line).

Surveying Tips and FAQ

Tips for Collecting Elevation Data

Use a vehicle where the GPS-to-ground offset will remain constant (such as a tractor, truck, or ATV – not a harvester or self-propelled sprayer that will shift vertically depending on load).
If the field you are surveying has wheel ruts, either stay in them or stay out of them. Do not alternate between them.
Do not survey in fields where there will be variable wheel sinkage – ie., if part of the field is wet and part is dry.
Trace the course of any waterways and banks you want to include in the elevation model. Drive the centerlines of such features, and also drive the shoulders.
Ensure that your base station is within 1.5 miles (2.4 km) of the area you are surveying.
Areas that exhibit a rapid change in slope will need to be surveyed more intensely (closer swatch widths)
Survey at a slow enough speed so the vehicle does not rock or bounce measurably.
If you are using an implement based receiver to survey with, DO NOT alter the elevation of the implement while surveying. If using a scraper mounted receiver, raise the blade to full height before starting the survey and leave it at this position for the duration of the survey.
Save your data as often as necessary. Consider how long it would take to re-do the work you would lose if your computer crashed at any point in the survey.
Use markers to set benchmark height/control points.
Collect elevation data on 30-50ft (9-15m) passes (no more than 80ft/24m). Complete more passes in areas of the field with detailed terrain.
Try not to double survey areas. Use the pause button to skip over the already surveyed area before recommencing.
Drop markers as required.
Points are logged once every 2 meters (6.6 feet). The data received between these points will be averaged. This reduces the effect of noisy GPS (bumpy ground or bouncy implements).
Preferably use 5Hz, as it will allow us to better compensate for noisy data.

Surveying FAQ

Q: Why are there gaps in the GPS surveyed data?

A: This can be caused because the GPS has stopped transmitting (check the connection) or it can be that the user has hit “Pause” or “Stop” on the T3RRA Display. Pausing can be used when one needs to stop surveying for a time and then resume from the same point. (i.e., for a lunch break)

Q: Are there any limits on logged data?

A: We will only record a data point once every 2 meters (6.6 feet). Any data received that’s less than 2m from the last logged point will be averaged into one record.

Q: What do we mean when we say we “average” the collected data into one record?

A: If we receive a GPS read every 50cm, we get 4 GPS reads every 2 meters. We take all of those data points and average their position (latitude and longitude) and their elevation to produce the dropped point. This allows us to compensate for the fact that the surface can be quite rough when surveying.

Q: Why does the logged point always appear about 1m behind the tractor?

A: This is because of the averaging. As we average the position as well as the elevation it will drop ½ the collection distance behind the tractor.

Surveying with extra sensors (T3RRA Survey only)

T3RRA Survey allows you to bring data in from additional survey types. When you hit the “start” button to begin surveying, you will be presented with various options.

Choose the first option (GPS data) if you don’t have anything additional to collect with.

After choosing your sensor, the collected elevation points will be based on the sensor, so you get a color gradient showing the collected sensor data. The “Current” in the top left of the screen will also show your current sensor value.

The GPS screen will allow you to debug the sensor data

After you’ve selected your sensor, surveying works the same as for the other tools, so read on to learn more about the available options to you.

How to export/view surveyed data

To export all the data gathered in the survey, go out to the wizard step and go to the final step “Export”. Currently, “CSV” and “PCT AgCloud” exports will allow the sensor data to be retrieved.

Map: Recent GPS Errors

In the top left of the screen, after a GPS error is encountered, an INFO hint will be shown.

Tapping on this text will open the GPS info window to show the recent errors. This is helpful if you have frequent but intermittent errors that happen too quickly to read the error messages.