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The current geodetic reference system in Kenya

The Department of Surveys is the official agency of the government of Kenya on all matters affecting land surveys and mapping. Its’ main functions are:-

  • To provide and maintain plans for property boundaries in support of the Land Registration throughout the country.
  • To provide all kinds of topographical and thematic maps in both rural and urban areas of the country for use by other Government Departments and the general public.

The department has been in existence since 1903.    

The current geodetic network in Kenya was established during the colonial times by the British. Since 1892, several major triangulation networks have been observed and computed by various organisations for specific purposes. Each organisation thus chose the coordinate system that appeared suitable resulting in a number of different systems. For each sizeable network, the readily available datum was used resulting in many datums for both planimetric and height control.

Doppler observations were carried out by the survey of Kenya between 1972 and 1973. The aim of the exercise was to:

  • Evaluate the accuracy of the primary controls in Kenya;
  • Provide geodetic control in remote and un-surveyed areas in the country;
  • Strengthen the triangulation with precise position at optimum spacing;
  • Contribute to the development of a single well fitting datum for the African continent.

The ITT 5500 equipment was used. Doppler positioning using precise ephemeris fixed fifteen stations distributed over the country.

The current geodetic network in Kenya is based on the 1960 Arc Datum. The coordinates are in UTM. There the two main reference ellipsoids used in Kenya are Clarke 1858 and Clarke 1880.

The datum for all heights in Kenya is the mean sea level referred to a tide gauge at Kilindini harbour in Mombasa. This gauge has however been submerged and a new one constructed and connected to some fundamental bench marks. By the year 2000, 3570km had been precisely levelled, the last 70km having been carried out by the Kenya Institute of Surveying and Mapping between 1992 to 1993.

There are three coordinates systems that have been used in Kenya:

  • The Cassini-Soldner coordinate system;
  • The east African war system; and
  • The UTM coordinate system.

Before 1950, nearly all triangulation networks were based on the Cassini-Soldner coordinate system; hence the cadastral surveys in Kenya were also based on this system.

The east African war system of coordinates was introduced as a military system for east Africa. Its main aim was to unify the coordinate system for the British Commonwealth territories in the south, east and central Africa to avoid discontinuity in topographical mapping and grid references across territorial boundaries. The coordinates in this system have since been converted to UTM system.

The UTM system was introduced in Kenya in 1950 by the directorate of overseas survey (D.O.S), when it began providing survey work in Kenya. The system used Clarke 1880 spheroid; the unit of measurement was the international metre. The survey of Kenya has made an effort to convert all points to this coordinate system.

Problems experienced with the current geodetic network

Some of the problems that have been experienced through the continued use of the current geodetic network include:

  • The existence of different coordinate systems has caused the need for regular coordinate conversion especially from Cassini to UTM system of coordinates;
  • Pillars located at hills have been difficult to access and many have been destroyed; the network is also low;
  • Lack of suitable points to base the transformation especially from Cassini to UTM;
  • Lack of information or data from previous work as the records of surveys carried before 1950 are not readily available;
  • Height data has been found not consistent having been derived from different datums;
  • Equipment used earlier had lower level of precision and the network is generally weak;
  • Hydrographical charts are not fully developed due to lack of controls near the Indian ocean, and around the lakes;
  • Points established by space techniques are relatively few;
  • Re-establishment of destroyed pillars has not been carried out fully due to high cost of classical triangulation method.

Minimizing the current problems of geodetic network

There is continued effort to solve the problems resulting from the current geodetic network. This has primarily been done using the Global Positioning Service (GPS).

Since August, 1996, Kenya Institute of Surveying and Mapping (KISM), under the mini-project has been carrying out GPS surveys on first order triangulation pillars in an attempt to establish transformation parameters between the WGS 84 ellipsoid and Clarke reference ellipsoid used in East Africa. The work is still ongoing but is experiencing problems due to lack of funds.

The Survey of Kenya is in the process of establishing continuous GPS observation stations in Kenya. The following table indicates the ongoing phase one construction of the continuous GPS observation stations:

FID

SHAPE

NAME OF COS LOCATION

SOC

REMARKS

1.

Point

LOKITAUNG

KEN

 

2.

Point

MOYALE

KEN

 

3.

Point

LODWAR

KEN

COMPLETED

4.

Point

MARSARBIT

KEN

STARTS IN 2 WEEKS

5.

Point

MERU

KEN

COMPLETED

6.

Point

MANDERA

KEN

 

7.

Point

WAJIR

KEN

 

8.

Point

GARISSA

KEN

COMPLETED

9.

Point

BONDO

KEN

COMPLETED

10.

Point

LIBOI

KEN

 

11.

Point

HABASWENI

KEN

 

12.

Point

LOKICHOGIO

KEN

 

13.

Point

SABAREI

KEN

 

14.

Point

RCMRD

KEN

COMPLETED

15.

Point

MALINDI

KEN

 

16.

Point

KANZIKU

KEN

 

17.

Point

EL WAK

KEN

 

18.

Point

MARALAL

KEN

STARTS IN 2 WEEKS

19.

Point

KAPENGURIA

KEN

 

20.

Point

KILGORIS

KEN

 

21.

Point

KAJIADO

KEN

 

22.

Point

WUNDANYI

KEN

COMPLETED

23.

Point

KWALE

KEN

COMPLETED

24.

Point

MALINDI

KEN

COMPLETED

25.

Point

ERDAMA RAVINE

KEN

COMPLETED

Level 1 or Phase 1 comprises of 25 stations of zero order accuracy with nine stations completed.

Level 2 or phase two comprise of 72 stations, first order accuracy, to be done later.

Level 3 or phase 3 comprise of 125 stations, 2nd order accuracy, to be done later

Others include 3rd and 4th order types of which they are numerous in number although most of the points in this category are distributed mostly in urban areas with minimal or random distribution in the rural areas.

The locations of some Stations were changed as shown in the table below.

No.

ORIGINAL LOCATION

NEW LOCATION

1.

SHIMONI

KWALE

2.

VOI

WUNDANYI

3.

ASEMBO

BONDO

4.

PARSELOI

MARALAL

5.

KAPENGURIA

KANYARKWAT

                                       

Dimensions

Base plate is 2.5mx2.5m at 1.0 m deep

Column is 0.6mx0.6m at 2.7m deep on the ground.

Existence of IGS stations

There are two continuous GPS observation stations connected to the IGS (International Geodynamic GPS Services) stations; one is in Malindi and the other in KISM (Kenya institute of Surveying and Mapping). The station at KISM is currently not working. The data from these continuous recording stations are used for the computations of the baselines and eventual coordination of all other points.

 Conclusion

The problems exhibited by the current geodetic network in Kenya can be solved through the integration of GIS and GPS in all mapping aspects of the country. There is need for political will and financing of the Survey of Kenya in its efforts to carry out GPS observation stations through out the country. There is also the need for the government to source from the British, the early records of their geodetic surveys carried out in Kenya during the colonial times; this will greatly enhance the efforts of Survey of Kenya in trying to update the current geodetic network. The continuous IGS observation station at KISM needs to be restored to full functionality to complement the one operating in Malindi.

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8 thoughts on “The current geodetic reference system in Kenya

  1. This is a good information, however, the Survey of Kenya should have picked up from where the KISM left. KISM established several GPS stations in Kenya and i think Survey of Kenya should have done densification.

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  2. the land survey tha was carried in kenya between 1972 to 1973 seems not to be accurate because the road from kangema -gachocho to gachage road was surveyed by british surveyors and was contrary to kenya government surveyors because the beacons were put in the peoples farms.ancesters died and burried in the areas purpoted to be in the road reserve,so if the lands were demacated contrary to the right measures even today, the survey of kenya is not accurate and have failed to meet the international survey standards, and if need to prove there are examples.

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  3. Solomon Njeru says:

    No way Micah Kamau, I would tell you with finality being i was the project surveyor who established the control network and subsequently did every inch of detail picking for topographical survey for design of the road and was also chief surveyor overseing construction-the survey work then was perfect. The previous control which were sparsely distributed for feasibility sturdy were done with Geodetic GPS and the road in question was falling in it spartial position as indicated on 1:50 000 sheets accurately .The above controls were used to distribute our to construction network. The ancentral graves and Mugumo trees were interfered by simply because of realignment of the new road in relation to the old and also the previous corridor was 30m and current one 40m. As you know this is one of the most challenging road due to crazy rugged terrain. The survey done previously those medival times was very good and the one we did was excellent. Construction entail quantities, geometric and survey cannot error an inch. Anyway this is survey jargon, please feel free to get in touch with me for any further clarification

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  4. KIPCHUMBA KIBOR says:

    THEN HOW COMES THE SURVEY CONTROL AT KISM AND THE BENCHMARK FOR LEVELLING AT SURVEY OF KENYA IS FUNCTIONABLE? I NEED AND ANSWER PLIZ!

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  5. STEPHEN NDEGWA says:

    I’m experiencing crazy problem in Rumuruti since the FR’S. are in Cassini soldner and there are no excel sheets for conversion from cassini to UTM ARC1960. Also the pillars around were destroyed by locals claiming there exist Gold and mercury underneath. If someone could be having sheet 106/1 please help me.

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