Control points to improve the accuracy of creating orthophotos

Geodetic control points are fixed points on the ground that possess a set of planimetric and elevation coordinates. Control points are used to refine the georeferencing of satellite and aerial images of the Earth's surface by measuring the coordinates of a distinctive object on the ground and identifying this object in the image.

Control points are a fundamental element in the process of creating accurate orthophotos and digital elevation models, ensuring their reliability and applicability in various fields, including land surveying, agriculture, construction, environmental monitoring, and many others.

Purpose:

Control points are necessary for obtaining accurate spatial coordinates of the Earth's surface or objects on it.

Ground control points allow achieving sub-meter accuracy in the georeferencing of satellite images and centimeter-level accuracy in the georeferencing of aerial photographs, as well as eliminating systematic distortions of onboard equipment.

The accuracy of georeferencing a satellite image using RPC coefficients is generally lower than the accuracy of creating an orthophoto of the corresponding scale. For example, the planimetric accuracy of a very high-resolution satellite image using RPC coefficients ranges from 7 to 30 meters depending on the imaging equipment. When measuring a single control point, the georeferencing accuracy of an orthophoto can reach up to 1 meter.

You can order from us

Satellite imagery. Satellite data

Digital elevation models (DEM)

Aerial & UAV imagery

Photogrammetric processing (Image Processing)

Object detection. Extraction of contour features

Goals:

Georeferencing satellite images to ground objects with known geographic coordinates allows for the accurate determination of the location of all objects in the image.
Correcting distortions caused by camera tilt, perspective, and terrain relief to ensure that images accurately reflect the real sizes and shapes of objects.
Creating orthophotos and maps that can be used for object interpretation, determining their planimetric coordinates, and making precise measurements of distances, areas, and other parameters without the need for additional distortion correction.
Integrating satellite images with other geospatial data, such as topographic maps, cadastral data, and GIS (Geographic Information Systems), for comprehensive territory analysis.

Objectives:

In the preparatory stage, a planimetric and elevation project is developed, defining the boundaries of the survey and the areas for control points.
On the ground, in the designated project areas, the identification and selection of clear terrain features that are easily recognizable in images of the corresponding resolution (e.g., power line pylons, corners of fences, curbs, etc.) are performed. In the field, less distinctive objects such as solitary trees or large rocks can be used as control points. For new surveys, artificial markers with high contrast relative to the terrain can be installed.
Accurately determining the geographic coordinates of the selected objects using geodetic methods and equipment, such as GNSS receivers (usually dual-frequency receivers with GPS/GLONASS navigation systems).
Measurement control.

Advantages of Using Remote Sensing Data

The use of archival and new high and very high-resolution satellite images with highly accurate orbital georeferencing allows for the creation of orthophotos with high accuracy and detail without the need for ground-based topogeodetic work to obtain control points. Satellite data can be obtained more quickly since they may already be available in the operator's archive.
The use of aerial photographs and images from UAVs/drones for creating orthophotos requires new surveys, which take more time due to the need for special permissions and fieldwork. However, orthophotos obtained from orthorectification of aerial photographs possess high visual informativeness and excellent measurement properties.

Prices for services

Consultation	free
Selection of control points (if necessary), preliminary analysis of initial data, additional and reference materials	free
Cost of creating an orthophoto	from 1 USD per 1 km², calculated individually for each specific order and depends on the amount of processed remote sensing data, the presence (absence) of control points, and the digital terrain model used
Cost of setting control points on the ground	The cost of setting control points on the ground is from 4,500 rubles per point and depends on the location of the area, execution time, and the number of points.
Execution time	From 10 working days (depends on volume, complexity category, availability of remote sensing materials, additional and reference materials)

Send a request

The cost of execution is calculated on an individual basis, taking into account a specific of task.

After receiving the task description, we calculate the cost and send you a commercial offer.

Period of execution

Agreement of issues, analysis of the availability of remote sensing data, additional and reference data	From 1 to 5 days^*
Contract signing	From 1 to 5 days^*
Image acquisition	From 2 to 10 days^**
Photogrammetric project planning	From 2 to 5 days^*
Determination of control point coordinates on the ground	From 15 days^*
Orthophoto creation	From 2 days^*
Preparation of a technical report on the work performed	From 1 to 12 days
TOTAL TIME	From 10 days

The completion time depends on the number of square kilometers and the type of product being created, the availability of archival remote sensing materials, additional and reference materials.

* working days
** from the date of receiving 100% advance payment for remote sensing materials

How to place an order:

STEP #1: Submit a request on the website specifying:
- territory (coordinates, district name, region, shp file, etc.);
- requirements (scale, detail, creation, update);
- requirements for remote sensing data, additional and reference data;
- execution time
STEP #2: Agree on the technical assignment and cost:
- Procurement of remote sensing data, images are paid separately (from 8 to 70 USD per 1 km² depending on the survey (archival-new, mono-stereo, resolution))
- agree on the technology of work execution, requirements for the created products
STEP #3: Sign the contract and start working:
- The start time for creating the orthophoto is from 5 working days from the date of receiving 100% advance payment for remote sensing materials - payment only by bank transfer.

We work with individuals and legal entities, individual entrepreneurs, government and municipal authorities, foreign customers, etc.

Need for consultation?

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Stages of service provision

Stage #0 (Before Contract Signing) – Rapid Assessment:

Agreeing on the task requiring the application of laser scanning technology;
Defining the area of interest;
Determining the purpose of the created product;
Agreeing on technical issues.

RESULT: possibility (YES/NO) of providing the service

Stage #1 (Before Contract Signing) – Development of Technical Specifications and Contract Draft:

Agreeing with the customer on remote sensing data available in operator archives or ordering new imagery;
Defining the work technology and agreeing with the customer on the methodology and timelines;
Agreeing on the coordinate system and projection requirements for the final product;
Agreeing with the customer on the technical specifications for the entire scope of work;
Final determination of labor costs and material expenses, agreeing on delivery times and costs.

RESULT: signed contract

Stage #2 (Contract Execution):

Receiving the advance payment;
Receiving the advance payment (100% prepayment for the purchase of remote sensing materials);
Ordering remote sensing materials;
Initial inspection of remote sensing materials;
Quality check of the materials received from the Customer;
Preparation, agreement, and approval of editorial and technical guidelines with the Customer;
If necessary – creating a geodetic work project for collecting coordinates of control points on the ground;
Geodesists' fieldwork for conducting on-site operations;
Creating digital orthophotos necessary for task completion;
Performing visual and automated quality control of the created product;
Exporting the created (updated) project into the required formats, projection, and coordinate system;
Writing a technical report.

The result of the provision of services

The customer receives the following results:

Original satellite images (if necessary) with metadata file and RPC coefficients of the required spatial resolution;
Orthophoto of the area with the detail and accuracy of the required scale;
Technical report, including the composition, stages, and control of the completed work;
Geodetic work report, including sketches, photographs of points on the ground, and a list of their coordinates.

The results are delivered on HDD/CD disks or via the Internet through FTP servers, and textual materials are provided in paper form to the customer's address.

Requirements for Source Data

Accurate geographic coordinates of the object in the required coordinate and elevation system (specialists from GEO INNOTER LLC will clarify the coordinates provided by the customer in any convenient form). If it is not possible to provide this information, the customer should specify the intended use of the received data, and specialists from GEO INNOTER LLC will analyze the requirements and propose the best solution.

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Completed projects

Creation of an orthomosaic for the city of Rostov-na-Don

2020.11.03

Recalculation of the catalogue of coordinates and geodetic points from USK-89 to MSC-89 (zone 2)

2023.09.12

View all projects

The material was checked by an expert

Zazulyak Evgeny Leonidovich

Engineer, 28 years of experience, Education - Moscow Topographic Polytechnic Technical School, St. Petersburg Higher Military Topographic Command School named after Army General A.I. Antonov, Military Engineering University named after V.V. Kuibyshev. Kuibyshev Military Engineering University.

Customers

FAQ

How are anchor points selected?

For reference points, clearly visible objects on the ground are selected - such as corners of buildings, road markings, railway crossings, etc. It is important that these objects are static and do not change their position over time.

How are the coordinates of reference points measured?

The coordinates of control points are usually determined using geodetic measurement methods, for example, using GNSS receivers. These measurements must be made with high accuracy.

How many points are needed?

The more control points there are and the more evenly they are distributed throughout the area, the higher the accuracy and quality of the orthomosaic. However, their number and distribution depend on the scale of the project, the terrain and the required accuracy.

What information is required to get started?

territory of interest (location/coordinates of the object in any convenient form, and area of the object);
a specific problem that needs to be solved using the products being created.

What are the deadlines for completing the work?

The duration of work on a set of reference points varies depending on the area and configuration of the territory of interest, as well as its remoteness and transport accessibility.

How is payment made?

100% prepayment of the invoice after signing the contract.