GNSS RTK Surveying in Turkey: TUSAGA-Aktif CORS Guide 2026

Turkey's surveying sector is driven by three primary demand streams that require consistent GNSS deployments across the country's 783,000 square kilometres.

INFRASTRUCTURE AND CONSTRUCTION:
The Turkish government has invested heavily in transport and civil infrastructure over the past two decades. Your GNSS operations will likely intersect with one of these key ongoing programmes:

• Highway and motorway expansion across the Anatolian network.
• High-speed rail corridors connecting Istanbul, Ankara, Konya, and Izmir.
• Istanbul Canal: a 45 km artificial waterway requiring precise geotechnical and alignment surveying.
• Urban renewal: mass housing and urban transformation projects driven by TOKI (Housing Development Administration).
• Energy infrastructure: hydropower dams in the east, wind farm foundation setting in the west, and transmission corridor surveying.

CADASTRAL SURVEY:
Turkey has one of the highest property transaction volumes in the region. TKGM (Tapu ve Kadastro Genel Müdürlüğü) administers a continuous cadastral renewal programme involving detailed parcel boundary surveys, legal subdivisions, and agricultural land consolidation (arazi toplulaştırma). For cadastral RTK work, the TUREF datum and correct projection must be applied — it is mandatory for Tapu (land registry) compliance.

EARTHQUAKE MONITORING AND RECONSTRUCTION:
Following major seismic events, precision GNSS is deployed for damage assessment, structural monitoring, and rebuilding setting-out. Given Turkey's seismically active geology, this application is an ongoing necessity.

Surveying accurately in Turkey requires understanding its geodetic backbone. Turkey uses TUREF (Turkish Reference Frame) as its official national geodetic datum. Adopted in 2001, it is aligned to ITRF96 at epoch 2005.0.

DATUM PARAMETERS:

• Ellipsoid: GRS80
• Reference frame: ITRF96, epoch 2005.0
• Relationship to WGS84: TUREF and WGS84 are closely aligned. Differences are typically at the centimetre level. For general engineering and earthmoving, WGS84 can often serve as a workable approximation. However, for cadastral operations and legal surveys submitted to TKGM, you must select TUREF explicitly.
• Previous datum: ED50 (European Datum 1950) was historically used throughout Turkey. If your project references legacy ED50 coordinates, a datum transformation is required. Never mix ED50 and TUREF coordinates within the same dataset without applying a strict transformation.

IN APEKSURV:
Select TUREF by navigating to Project → Coordinate System. The datum is pre-loaded in the APEKS coordinate library. For legacy ED50 projects, apply the official ED50-to-TUREF transformation parameters available in ApekSurv. Always confirm the datum used in design drawings with the project engineer before starting work.

ED50 NOTE:
A significant volume of existing Turkish cadastral maps and older engineering drawings still reference ED50. The coordinate shift between ED50 and TUREF is approximately 100 to 200 metres depending on location. A datum mismatch at this scale will produce obviously incorrect results. Always double-check the governing datum.

When operating your GNSS RTK setup in Turkey, understand the three primary coordinate systems in active use.

UTM (UNIVERSAL TRANSVERSE MERCATOR):
This is the standard projection for engineering, construction, and infrastructure projects. Turkey spans multiple zones:

• UTM Zone 35N: Western Turkey (Istanbul's European side, Izmir, Bursa, Ankara).
• UTM Zone 36N: Central and Eastern Turkey (Istanbul's Anatolian side, Konya, Kayseri, Gaziantep, Diyarbakır).
• UTM Zone 37N: Far Eastern Turkey (Van, Erzurum, Hakkari).

Most infrastructure projects specify Zone 35N or 36N. Confirm the zone with the project engineer, particularly near zone boundaries.

TURKISH NATIONAL GRID (3-DEGREE GAUSS-KRÜGER):
The legal cadastral system uses a 3-degree Gauss-Krüger projection divided into 6 zones (central meridians 27°, 30°, 33°, 36°, 39°, 42°). This system is used for all formal Tapu cadastral submissions. All six zones are pre-loaded in ApekSurv.

IN APEKSURV:
Select the correct projection in Project → Coordinate System when creating a new job. For cadastral submissions, use the Gauss-Krüger zone corresponding to your longitude. For engineering and infrastructure, use UTM Zone 35N, 36N, or 37N as appropriate.

To achieve centimetre-level accuracy without a local base station, you rely on TUSAGA-Aktif (Türkiye Ulusal Sabit GNSS İstasyonları Ağı - ...). This is Turkey's national CORS network, operated jointly by HGK (Harita Genel Komutanlığı) and TKGM.

NETWORK SPECIFICATIONS:

• 146 continuously operating reference stations covering the full national territory.
• Average station spacing approximately 100 km, providing a robust geometric web.
• Coverage is dense in Western Turkey, adequate across Central and Eastern Anatolia, and good in border regions.
• The network provides VRS (Virtual Reference Station) corrections for improved accuracy across the grid.

SUBSCRIPTION:
TUSAGA-Aktif requires a paid subscription — it is not a free public service. Two primary tiers are available: individual surveyor licence and corporate/institutional licence. Apply by contacting HGK or TKGM via tusaga-aktif.gov.tr. Allow 5–10 working days for account activation. International firms must submit formal company registration documentation translated into Turkish.

NTRIP SERVER DETAILS:

• Server address: www.tusaga-aktif.gov.tr
• Port: 2101
• Format: RTCM 3.x (multi-constellation compliant)
• VRS mountpoints are widely available and recommended.

BASELINE RECOMMENDATION:
With 146 stations, the majority of Turkey has baseline distances well below 70 km. For remote Eastern Anatolia projects, verify the nearest station distance before mobilisation. If baselines exceed 70 km, deploy an APEKS MAX5 base station to generate local UHF corrections.

Elevation accuracy in civil engineering is critical. Turkey mandates the TG03 geoid model (Turkish Geoid 2003) for converting raw GNSS ellipsoidal heights to orthometric heights referenced to the Turkish national vertical datum.

WITHOUT GEOID MODEL:
Standard GNSS elevation output is an ellipsoidal height above the GRS80 ellipsoid. In Turkey, the geoid separation (N value) varies from approximately +30 m to +50 m, with larger separation in mountainous eastern Turkey. Using ellipsoidal heights directly introduces systematic elevation errors of up to 50 metres.

IN APEKSURV:
Apply TG03 by navigating to Project → Coordinate System → Geoid Model. APEKS receivers ship with TG03 natively in the pre-loaded geoid library. Select it explicitly. Do not substitute the global EGM2008 model for projects requiring the Turkish national vertical datum — differences can exceed 0.3 m locally, particularly in eastern Turkey, compromising vertical tolerances.

CONSTRUCTION ELEVATION NOTE:
For projects in Istanbul and the Marmara region, confirm whether the project uses the national vertical datum or a local construction benchmark. Major infrastructure contracts typically specify the national datum, but local urban renewal projects may tie into municipal benchmarks. Always confirm before recording elevation data.

VERIFICATION:
Check your RTK elevation against a known levelled benchmark at the start of each daily session. The vertical difference should fall within ±25 mm. If the discrepancy exceeds 50 mm, halt work and recheck your TG03 selection immediately.

An RTK receiver in Turkey is a versatile tool. Here is how precision GNSS is deployed across the primary surveying sectors:

1. HIGHWAY AND MOTORWAY CONSTRUCTION:
Turkey's ongoing motorway network expansion requires RTK for alignment surveying, earthworks setting-out, and as-built documentation across the Anatolian plains. These long linear projects benefit from RTK's ability to cover kilometres of alignment without frequent instrument moves. The APEKS AP40 Laser+, with its 120° IMU, is frequently used for rapid slope stake setting on cut-and-fill embankments.

2. CADASTRAL PARCEL SURVEY:
TKGM's continuous cadastral renewal programme demands strict RTK precision for parcel boundary reinstatement and new subdivisions. The TUREF datum and the correct 3-degree Gauss-Krüger projection must be applied for Tapu submission. A licensed cadastral surveyor must formally sign off on all submissions.

3. URBAN RENEWAL AND TOKI PROJECTS:
Mass housing projects under the TOKI banner require rapid, accurate RTK deployments for building setout, infrastructure layout (sewage, power lines), and as-built surveys across large development sites.

4. EARTHQUAKE RECONSTRUCTION:
Following the major 2023 Kahramanmaraş earthquakes, RTK surveying remains deployed for damage assessment, structural monitoring, and reconstruction setting-out across affected regions in southern Turkey. The IP67/IK08 rugged rating of APEKS receivers handles the harsh, dust-heavy construction environments.

5. ENERGY INFRASTRUCTURE:
From wind farm construction in the Aegean and Black Sea regions to hydropower dam projects in eastern Anatolia and transmission corridor surveys, precision RTK is used for foundation setting-out and alignment.