Camacupa EarthCache

Cartography is a science in the base of Geology. Without good positioning no maps would have been drawn, without maps, Geology would just be a useless collection of dusty rocks, minerals and fossils.

This Earth cache is a memento to all cartographers, particularly the Portuguese ones of old times. Yes, I have a special bias towards the Portuguese navigators and cartographers of XV and XVI centuries that opened the world seas and charted the coastlines and, in varying degrees the hinterland, of Europe, America, Africa, Asia and Oceania (Antarctica was much too cold…). They have done all this with magnetic compasses and astrolabes, without satellites, GPS, laser based devices or cell phones. No hints or spoilers in web pages, they just had intelligence and courage. Those were true geocachers; Earth discovery was their treasure.

This cache in the exact center of Angola is also a recognition of the warmth and “joie de vivre” of the Angolans, a people with whom we Portuguese share History and with whom we mixed the blood, values and culture.

Cartography’s central function, spatially structuring geological knowledge, is very visible in Economical Geology. Two Angolan examples I have faced:

1.        Alluvial diamond mineralization occurs in clusters: diamond concentrate in morphological traps (e.g. bedrock depressions, old river channels, potholes, etc.). Given this erratic mineralization nature, a precise conversion from the older Angolan coordinate systems Camacupa-based into modern systems is is crucial for mine planning and resource evaluation based on old (but extremely valuable) exploration data, only crudely geo-referenced. In the not very distant past, 200 to 300 m positioning errors (due to bad conversions) were common, leading to erroneous decisions and consequently to an unjustified credibility loss of past exploration data.

2.        Kimberlites are rare rocks; diamond mineralized kimberlites are even rarer bodies; economic primary diamond deposits are counted by a few dozens. Kimberlite bodies have small outcrops, with areas above 30 ha being quite uncommon. An economic kimberlite being crossed by the line separating two concessions seems an impossible event. Well, it happened in Angola (and elsewhere). In Angola, with potentially imprecise coordinate systems conversions (from Camacupa based to WGS 84), this may lead millions of dollar losses to one of the sides (and gains to the other) of the concession borders.

This particular case led me to investigate and evaluate the available conversion algorithms (ArcGIS has ten and I have found others). Later on I visited the Camacupa’s datum origin. This cache is a secondary result of this work.

Located in the geographical center of Angola, Camacupa is an important locality. The region is crossed by the railway (Caminho de Ferro de Benguela), on its way from the Lobito harbor in the Angolan coast to Luau in the Eastern border of Angola and further to Central Africa (Zambia and RDC). The complete rehabilitation of the 1301 km long railroad to Moxico County is estimated to be concluded in 2012. Camacupa has also an economic potential based on agriculture and mining. This entire region will bloom, as soon the trains start moving again.

Camacupa also has the distinction of being the Angolan geographical center and the origin of the Camacupa datum, used in most Angolan maps. The (somewhat technical) description Camacupa datum has been based on a paper by Clifford J. Mugnier published in Photogrammetric Engineering & Remote Sensing (March 2001).

The Camacupa Datum of 1948 is based on the origin at Campo de Aviação (airfield) where f₀ = 12° 01' 19.070" South, ?₀ = 17° 27' 19.800" East of Greenwich, and ho = 1508.3 m.

Thanks to John W. Hager, “This is the principal vertex marked by a concrete monument, constructed on a high part of the Camacupa Air Field, immediately to the north of the runways.” (This is) “defined as the “Datum Point” of the main triangulation network of Angola. A concrete monument with the dimensions 70 ´ 60 ´ 100 cm (length E-W ´ width N-S ´ height), topped by a white marble slab on which is cut in black: M.G.A. –P.F.- 1948; in the center of which is placed the top mark of the base, which is defined as the extreme West of the Geodetic Base of Camacupa. The mark found here is protected by a masonry casing with a metallic cover, easily removed to permit observations over the base when necessary.” Remarkably, some Datums established by the Portuguese in Angola (and Mozambique) were referenced to the Clarke 1866 ellipsoid (the same as used in the U.S. for the North American Datum of 1927) where a = 6,378,206.4 m and b= 6,356,583.8 m.

Other datums existing in Angola include the Lobito Datum of 1937 based on the origin point at the astronomical pillar Restinga do Lobito, Extremo NE da Base do Lobito, where f₀ = 12° 19' 00.86" South, ?₀ = 13° 34' 45.67" East of Greenwich, Clarke 1866 ellipsoid. Dr. José Carvalho of Maputo, Mozambique states that the Camacupa Datum of 1948 coordinates of the same point are f₀ = 12° 19' 01.357" South, ?₀ = 13° 34' 58.375" East of Greenwich.

The transformation from the Lobito 1937 Datum to the WGS 84 Datum is DX = –256.73 m, DY = 0.00 m, and DZ = –103.67 m (±10 m).

The Luanda Datum is based on the origin point at Luanda Observatory where F0 = 08° 48' 46.8" South, ?₀ = 13° 13' 21.8" East of Greenwich, Clarke 1866 ellipsoid. The Moçamedes Datum of 1956 origin point is at the Moçamedes Meteorological Station where f₀ = 15° 11' 16.34" South, ?₀ = 12° 07' 34.53" East of Greenwich, Clarke 1866 ellipsoid.

To log this cache you have to:

1. E-mail me a picture of you (with your GPS) next to the statue nearby.

2. This cache is about coordinate conversion (and diamond deposits). E-mail me the Camacupa origin point coordinates in both the WGS84 and WGS72 Map Datums.

3. The Camacupa Datum origin is located inside the Lucapa Corridor (don't confuse it with the Lucapa Graben), a belt of kimberlites and carbonatites extending from SW Angola into Mbujy-Mayi (RDC). The statue next to the datum origin is made of a rock: that rock's most abundant mineral is also a characteristic mineral of a certain type of  kimberlites. What is the mineral in question?