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PHOTOGRAMM ETRIC ENGINEERING & REMOTE SENSING F e b r u a r y 19 9 9 1 2 7

C O L U M N

G r i d s & D a t u m s

The Republ ic of M auri t iusThe contents of this column reflect the views of the au-thor, who is responsible for the facts and accuracy ofthe data presented herein. The contents do not neces-

sarily reflect the official views or policies of the Ameri-can Society for Photogrammetry and Remote Sensingand/or the University of New Orleans.

T h i s mo n t h s t o p i c f ea t u res t h eRep u b l i c o f M au r i t i u s , an i s l an d n a -t i o n i n t h e I n d i a n O c e a n t h a t i n -c l u d es Ro d r i g u es I s l an d , t h e Ag a l eg aI s l an d s , an d t h e Carg ad o s Cara jo sS h o a l s (S a i n t Bran d o n ) . D i sco v eredb y t h e P o r t u g u ese i n t h e ea r l y 1 6 th

c e n t u r y, M a u r i t i u s w a s o c c u p i e d b yt h e Du t ch f ro m 1 5 9 8 -1 7 1 0 , an d wash e l d b y t h e F r e n c h f ro m 1 7 1 5 u n t i l1 8 1 0 w h e n i t w a s c a p t u r e d b y t h eBr i t i sh . M au r i t i u s was fo rmal l yc e d e d t o t h e U n i t e d K in g d o m i n1 8 1 4 . It b e c a m e i n d e p e n d e n t i n 1 9 6 8 ,a n d b e c a m e a r e p u b l i c i n 1 9 9 2 . T h i sn a t i o n h as a l an d a r ea o f 1 ,8 5 0sq u are k i l o met e r s , wh i ch i s a l mo s t11 t i mes t h e s i ze o f Wash i n g t o n , DC.

T h e f i r s t t r i an g u l a t i o n was ca r r i edo u t b y t h e a s t ro n o mer, Mo n s i eu rLAbbe La Cai l l e ( l i teral l y Mist erAb b o t o f t h e Qu a i l ) , wh en h e wass e n t t o t h e i s l a n d b y t h e F r e n c h E a s tIn d i a Co mp an y i n 1 7 5 3 . He o b se rv edt h e p o s i t i o n o f h i s o b se rv a t o ry(M ab i l e s h o u se ) , wh i ch w as s i t u a t ed4 ,7 3 0 f eet eas t an d 2 ,6 1 0 f ee t n o r t ho f t h e P o r t L o u i s Ti me Ba l l , a s : F o= 2 0 0 9 4 2 S o u t h , L o = 55 08 15E as t o f P a r i s . He d e t e rmi n ed t h esu m mi t o f L e P o u ce as o n e o f ap -p ro x i m at e l y 9 0 s t a t i o n s . No t e t h a tL e P o u ce l i t e r a l l y mean s t h et h u m b i n E n gl i s h , w h i c h i s a n a p r o -p o s d esc r i p t i o n o f i t s sh ap e! I g u esst h a t t h e Gr i d sy s t em u sed b y L aca i l l e( m o d e r n s p e l l i n g ) w a s b a s e d o n t h eB on n e p r o j ec t i o n , w h i c h w a s i nv o gu e w i t h t h e F r e n c h a t t h a t t i m e .

Un fo r t u n a t e l y, t h e r eco rd s o f L aca i l l e s su rv ey d i d n o t su rv i v e t h erav ag es o f t i me .

In 1 8 7 4 , Lo rd L i n d say l ed an ex -p e d i t i o n t o M a u r i t i u s t o o b s e r v e t h et r an s i t o f Ven u s ac ro ss t h e l o ca l me-r i d i a n . T h e p u r p o s e w a s t o o b s e r v e an e t w o r k o f p r e c i s e ly d e t e r m i n e d l o n -g i tu d e s i n t h e I n d i a n O c e a n . T h ep o i n t s o n M a u r i t i u s i n c l u d e dBel mo n t (p r i mary ) , P amp l emo u sses ,

a n d S o l i t u d e . O t h e r s i n t h e n e t w o r k w e r e t h e i s l a n d o f Ro d r i gu e s a n d t h eF r e n c h i s l a n d s o f R u n i o n a n d S t .

P au l . I n t e r es t i n g l y, t h e d a t u m o r i g i ni n E g y p t (d i f fe r en t Br i t i sh n e t wo rk an d d ecad e) i s s t i l l n am ed Ven u s .

In 1 8 7 6 , t h e S u rv ey o r Gen era l o f t h e Co l o n y o f M au r i t i u s , M . Co n n a l ,p u b l i s h e d c o o r d i n a t e s o f t h e s e c o n dt r i a n gu l a t i o n a n d u s e d t h e D at u mo r i g i n a s L e P o u ce , wh ere : F o = 2 0 11 4 9 .1 5 6 S o u t h , L o = 57 313 9 .6 0 Eas t o f Green w i ch . T h e e l l i p -so i d o f r e f e r en ce was t h e Besse l 1 8 4 1wh ere t h e sem i -maj o r ax i s (a ) =6 ,3 7 7 ,3 9 7 .1 5 5 met e r s an d t h e r ec i p -ro ca l o f f l a t t en i n g ( 1 / f ) = 299 .1528128 .T h i s p o i n t w a s a l s o t h e p r o je c t i o no r i g i n o f t h e f i r s t Cass i n i -S o l d n erGr i d S y s t em o f M au r i t i u s , an d wasu s e d w i t h a q u a d r a n t s y s t e m (n o r t h -so u t h , eas t -wes t ) , r a t h e r t h an wi t ht h e mo re mo d ern F a l se Eas t i n g san d F a l se No r t h i n g s .

In 1 9 0 2 , Cap t a i n Har r i so n o f t h eBr i t i sh Co l o n i a l S u rv ey S ec t i o n p ro -d u ced a se r i e s o f 1 i n ch ( t o t h emi l e ) map s a l so u s i n g L e Po u ce ast h e o r i g i n , b u t b ased o n t h e C l a rk e1 8 5 8 e l l i p so i d . Har r i so n s map p i n g ,p resu mab l y a l so u s i n g t h e Cass i n i -S o l d n e r G r id , w a s b a s e d o n t w o n e t -wo rk s o f t r i an g u l a t i o n t h a t weren e v e r c o n n e c t e d t o f o r m a c o n s i s t e n tsy s t em. T h e b as i s o f a l l su b seq u en tc o n t r o l an d m a p p i n g p r i o r t o t h e1 9 9 0 s w a s b a s ed o n y e t a n o t h e rsu rv ey.

In 1934 , Capt ain V. E . H. Sanc eau ,R .E ., p e r fo rmed t h e r e - t r i an g u l a t i o no f M au r i t i u s . He o r i g i n a l l y i n t en d edt o u se Co n n a l s wo rk as t h e b as i s o f h i s s u r v e y i n t h a t m o r e c o m p l e t er e c or d s e x i s t e d t h a n o f t h e w o r k o f t h e Co l o n i a l S u rv ey Sec t i o n . E v en -t u a l l y, o n l y t h e l a t i t u d e a n d l o n g i -t u d e o f L e P o u c e a n d t h e a z i m u t h L ePou ce Corps d e Garde (Lacai l lesRo ck ) were r e t a i n ed . T h e o n l y ad d i -t i o n a l p o i n t s o r i g i n a l ly u s e d i nCo n n a l s su rv ey t h a t w ere o ccu p i edb y S a n c e a u w e r e : Si g n a l M o u n t a i n ,Lagrave (th e g rave) , Mon tagneBl an ch e (wh i t e mo u n t a i n ) , No u v e l l eDeco u v er t e (n ew d i sco v ery ) ,M o n t ag n e Co co t t e (ch u ck -ch u ck o r

C L I F F O R D J . M U G N I

h e n m o u n t a i n ), M o n t a g n e B am b o u(b amb o o mo u n t a i n ) , an d t h e Wes tP eak o f t h e F ay en ce M o u n t a i n s . T h e

n ew t r i an g u l a t i o n o f M au r i t i u s e s t ab -l i sh ed t h e L e P o u ce Da t u m o f 1 9 3 4wi t h an o r i g i n o f: F o = 20 11 42 .25S o u t h , L o = 57 31 18 .58 East o f Green wi ch . T h e e l l i p so i d o f r e fe r -en ce was t h e C l a rk e 1 8 8 0 , wh ere a =6 ,3 7 8 ,2 4 9 .1 4 5 met e r s an d 1 / f =2 9 3 .4 6 5 . S an ceau s t r i an g u l a t i o n a l soe s t a bl i s h e d a n e w G ri d b a s e d o n t h eL amb er t Co n i ca l Or t h o m o rp h i c (Co n -fo rmal Co n i c ) wh ere t h e sca l e f ac t o ra t o r i g i n was 1 .0 ( t an g en t co n i c ) , an dt h e F a l se E as t i n g (F E) an d F a l seNo r t h i n g (F N) were 3 ,5 0 0 ,0 0 0 f ee t

e a c h . T h e u n i t o f m e a s u r e w a s t h ey ard , wh ere 1 me t e r = 1 .0 9 3 6 2 3 11y ard s . Cap t a i n S an ceau a l so p ro -d u c e d T h e 1 To p o g rap h i ca l M ap .

In 1 9 4 3 , t h e Un i t ed S t a t e s Arm y,Off ice o f the Ch ief o f Engine ers i s -s u e d t a b l e s o n t h e M a u r i t i u s Z o n ew i t h t h e F N a n d F E b e i n g1 ,1 6 6 ,6 6 6 .6 7 y a rd s . I t was n o t ed t h a tt h e n e w F N a n d F E of t h e O r d -n a n c e S u r v e y m a p s w e r e e q u a l t o1 ,0 0 0 ,0 0 0 met r es o n t h e B l u e Gr i d .

Acco rd i n g t o D . Ramasawm y,Ch i e f S u rv ey o r :

Du r i n g 1 9 6 2 -6 4 t h e Di r ec t o ra t eo f Ov er seas S u rv ey s (DOS ) UK u n -d e r t o o k a Te l l u ro met e r t r av e r seu s i n g mo s t o f Cap t a i n S an ceau st r i go n o m e t r i c p o i n t s a n d a t t h esame t i me es t ab l i sh i n g ab o u t 6 0n e w a d d i t i o n a l p o i n t s . D u r i n g th ep e r i o d 1 9 6 7 - 6 9 w i t h t h e a s s i s t a n c eo f DOS , t h e co n t ro l p o i n t s werei n c reased b y a fu r t h e r 8 0 p o i n t s .Du r i n g t h e same p e r i o d , a p r i maryl ev e l n e t wo rk was es t ab l i sh ed fo rt h e i s l a n d .

F o rmer l y, a l l co l o r map s o f

M a u r i t i u s w e r e p r o d u c e d b y D OSa n d l a t e r o n , t h e F r e n c h I n s t i t u tG `o g rap h i q u e Na t i o n a l ( IGN) a l sop r o d u c e d s o m e m a p s . T h e s c a l e o f t h ese map s were 1 : 1 0 0 ,0 0 0 (o n es h e e t c o v e r in g t h e e n t i r e i s l a n d )an d 1 : 2 5 ,0 0 0 (1 3 sh ee t s co v er i n gt h e w h o l e i s l a n d ) . I t w a s o n l y d u r -i n g t h e ea r l y sev en t i e s t h a t t h ef i r s t 1 :2 ,5 0 0 map s o f t h e u rb an

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