Phn m u

CC O C V BN

GII THIU h quy chiu v h to quc gia

I. M U

Xc nh h quy chiu tc l xc nh gc to v h trc c s to da vo c th biu din c tt c cc im trong khng gian. Mt h quy chiu c gi l ph hp vi phm vi lnh th ang xt nu t c 3 tiu chun sau:

C lch nh nht theo mt ngha ton hc no gia m hnh ton hc v khng gian vt l ca th gii thc.

Thun tin s dng trong thc tin c lu ti cc tp qun hnh thnh t lch s v tnh ph cp trn th gii.

D dng tnh ton chuyn i vi cc h quy chiu ang s dng m c bit l h quy chiu ton cu hin hnh.

Bi ton xc nh h quy chiu v h to c a v dng c bn l:

1. Xc nh mt ellipsoid quy chiu c kch thc ph hp (bn trc ln a v bn trc nh b, hoc bn trc ln a v dt f=(a-b)/a) c nh v ph hp trong khng gian thng qua vic xc nh to tm ca ellipsoid (X0, Y0, Z0) trong h ton cu. i vi Ellipsoid Ton cu cn phi xc nh cc tham s vt l: hng s trng lc GM, khi lng tri t M, tc quay tri t (, th trng lc thng Uo, gi tr trng lc thng trn xch o (e v trn cc (p.

2. Xc nh php bin i ph hp t h quy chiu mt ellipsoid v h quy chiu mt phng thnh lp h thng bn c bn quc gia bao gm c h thng phn chia mnh v danh php tng t bn theo tng t l.

3. X l ton hc cht ch li cc im to bao gm tt c cc loi tr o c lin quan sao cho m bo chnh xc cao nht.

Xy dng h quy chiu v h to quc gia l mt vic quan trng i vi mi quc gia. Trc ht y l c s ton hc mang tnh chun th hin chnh xc cc th loi bn nhm m t trung thc cc thng tin iu tra c bn ca t nc. H quy chiu v h to quc gia cn ng vai tr ht nhn trong h thng qun l hnh chnh lnh th, phc v gii quyt tt cc vn phn nh v qun l bin gii quc gia, a gii hnh chnh cc cp cng nh ranh gii ca tng tha t. Trong i sng ca mt x hi hin i h quy chiu v h to quc gia cn phi p ng cho hot ng ca cc ngnh nhm pht trin kinh t nh nghin cu vt l tri t, quan trc hot ng v tri t, m bo hng hi, dn ng hnh khng, b tr xy dng cc cng trnh, quan trc bin dng cng trnh, qun l cc mng li hot ng kinh t theo lnh th, v.v. H thng ny c vai tr quan trng trong cc hot ng m bo an ninh - quc phng. Hn na cc hot ng ca c dn trong cng ng cng cn ti mt h to thng nht nh nh bt c, i rng, giao thng, v.v. Vic xy dng h quy chiu v h to quc gia cn c ting ni chung ca cc ngnh v y l mt h thng a mc tiu.

Trong bo v t quc v xy dng t nc vic xc nh mt h quy chiu v h to thng nht lun phi i trc mt bc. Khi mi t chn n Vit nam Php tin hnh ngay vic xy dng h quy chiu v h to quc gia vi ellipsoid Clarke, im gc ti H ni, li chiu to phng Bonne v li cc im to c s ph trm c ng dng. M t chn ti Min Nam nc ta cng xy dng ngay h quy chiu v h to quc gia vi ellipsoid Everest, im gc ti n , li chiu to phng UTM v li cc im to c s ph trm ton Min Nam. Sau ngy ho bnh lp li Vit nam (1954) Chnh ph ta quyt nh thnh lp Cc o c v Bn Nh nc c nhim v chnh trong giai on u l xy dng h quy chiu v h to vi ellipsoid Krasovski, im gc theo h thng X hi ch ngha, li chiu to phng Gauss v li cc im to c s c chnh xc cao ph trm ton Min Bc.

II. QU TRNH XY DNG H QUY CHIU V H TO QUC GIA VIT NAM

Qu trnh xy dng h quy chiu v h to quc gia nc ta c phn ra cc giai on nh sau:

II.1 GIAI ON 1959 - 1975

Trong giai on ny Cc o c - Bn nc ta vi s gip trc tip ca Tng cc Trc hi Trung quc xy dng li cc im to c s theo phng php tam gic o gc truyn thng ph trm ton Min Bc dng li tam gic hng I (mt khong 250 Km2 c 1 im) v li tam gic hng II (mt khong 100 Km2 c 1 im). Song song vi li to , li cao hng I v hng II cng c xy dng ph trm Min Bc. H to - cao ny c chnh xc kh cao v p ng mi nhu cu i hi ca thc tin pht trin kinh t v bo v t nc.

II.2 GIAI ON 1975 - 1991

Sau ngy thng nht t nc (1975) Cc o c v Bn Nh nc tip tc pht trin li to trn vo cc tnh pha Nam p ng nhu cu pht trin kinh t. Li tam gic o gc hng I c pht trin ti Nng v li tam gic o gc hng II dc theo cc tnh duyn hi Min Trung cho ti Thnh ph H Ch Minh. p ng cung cp to kp thi cho cc ngnh v cc a phng, li to ph trm cho min Nam c xy dng theo tng li nh gi nhau, to im cui ca li trc l to khi u ca li sau, thm ch ti ng bng Nam b cn phi chn 2 im khi u l cc im gn ng c tnh chuyn t Min Bc vo (im 64629 - Nh th Hnh Thng Ty ti Tp. H Ch Minh lm khi u cho li to ng Nam b, im II-06 ti An giang lm khi u cho li to Ty Nam b). y l mt tn ti lch s ng nhin phi tri qua, ng thi cng l nguyn nhn lm cho h thng to hin ti H Ni - 72 thiu tnh thng nht, mt im c th c vi to tham gia vo cc li a phng khc nhau c lch ln nht ti trn 10m. Song song vi li im to , Cc o c - Bn Nh nc tin hnh xy dng li im cao hng I, hng II ni di t Min Bc.

chnh l chnh xc mt li to quc gia cn phi o li cc im thin vn (kinh , v v phng v) vi mt khong 18.000 Km2 c 1 im, li im trng lc c s v chi tit, li im trc a v tinh. Trc y Tng cc Trc hi Trung Quc gip ta o c cc im thin vn mt cho khu vc Min Bc. T sau nm 1975 Tng cc Trc a - Bn Lin x c tip tc gip ta o c mt cc im thin vn ph kn khu vc pha Nam, xy dng li trng lc c s ton quc c o ni vi li quc t v o mt s li trng lc chi tit, xy dng li trc a v tinh Doppler.

II.3 GIAI ON 1991 - 1994

Vo nm 1991 Cc o c - Bn Nh nc quyt nh a cng ngh nh v ton cu GPS (global positioning system) vo p dng Vit Nam hon chnh h thng to quc gia. Li to c s ti cc a bn cha ph li l Ty nguyn, Sng b, Minh hi trn t lin v li to bin trn tt c cc o chnh ti tn 21 o thuc qun o Trng sa c xy dng bng cng ngh GPS. n nm 1993 trn a bn c nc c ph kn cc li thin vn, trc a, trng lc, v tinh, s liu tnh ton chnh l h quy chiu v h to quc gia.

T 1992 n nm 1994 cng trnh tnh ton bnh sai li thin vn - trc a - v tinh c nc c tin hnh. Kt qu chnh ca cng trnh ny l: xc nh h quy chiu ph hp vi lnh th Vit Nam bao gm ellipsoid Krasovski nh v theo li v tinh Doppler, im gc ti im thin vn Lng, li chiu to phng Gauss - Kruger nh ang s dng; xc nh lch dy di (, ( v d thng cao ( theo cc s liu thin vn - trc a - trng lc chnh xc phc v chuyn cc tr o t mt t t nhin v ellipsoid quy chiu; kim tra li ton b tp hp tr o ton li, loi tr cc sai s th, chuyn ton b cc tr o v mt ellipsoid quy chiu v mt phng; bnh sai tng th cc tr o gc, cnh, phng v, doppler, GPS ca ton li trn mt phng Gauss - Kruger theo phng php chia nhm iu khin; nh gi chnh xc to tt c cc im trong li.

II.4 GIAI ON 1994 - 1999

Khi xem xt vic hon chnh h quy chiu v h to quc gia, Tng cc a chnh nhn thy mt s yu t mi v cng ngh cn nghin cu thm s la chn ph hp hn cho giai on pht trin tip theo. Cc nh hng sau y c xc nh:

1. Cng ngh GPS c xc nh l cng ngh nh v ca tng lai v s c p dng rng ri trong hu ht cc mc ch kinh t v quc phng, v vy h quy chiu cn xc nh ph hp vi vic p dng cng ngh GPS.

2. C th s dng ngay cng ngh GPS khong cch di xy dng li to c s cnh di c chnh xc cao hn hng I, mt mt kim tra li chnh xc cc tr o truyn thng v mt khc nng cao chnh xc h thng im c s to .

3. Xc nh chnh xc mi lin h gia h quy chiu quc gia vi h quy chiu quc t, to iu kin thun li gii quyt cc bi ton ton cu, khu vc.

4. Nghin cu xc nh mt h to phng hp l hn so vi h thng ang s dng, ph hp vi tp qun quc t.

Trong 2 nm 1996 v 1997 Tng cc a chnh quyt nh o li GPS cnh di chnh xc cao ph ln li to truyn thng xy dng, li ny c tn l li to c s cp "0". Cui nm 1998 n cui nm 1999 cng trnh xy dng h quy chiu v h to quc gia t chc nhiu hi tho quc gia tho lun cc kt qu t c. Cc kt qu ch yu l: tnh ton li ton b cc tr o GPS; s dng cc tr o GPS cp "0" kim tra cc tr o mt t, t pht hin cc khu vc c tr o khng t yu cu chnh xc tin hnh o b sung hoc o li; xy dng im gc ti H ni v o ni im gc vi li cnh ngn v li cp "0"; o to tuyt i trong h WGS-84 Quc t vi chnh xc to khong 1m ti 7 im phn b u c nc; o ni vi li to IGS quc t (trong h quy chiu WGS-84 Quc t) ti 6 im phn b u c nc; xy dng mt tp hp kh dy c cc im GPS c cao thu chun xy dng m hnh d thng cao Geoid, tnh ton lch dy di theo phng php ni suy thin vn - trc a - trng lc; la chn 25 im GPS c cao thu chun phn b u trn a bn c nc nh v ellipsoid quy chiu ph hp ti Vit Nam; la chn h quy chiu quc gia bao gm ellipsoid WGS-84, nh v ph hp ti Vit Nam, im gc ti H ni, li chiu to phng UTM, danh php bn theo h hin hnh c ghi ch danh php quc t; bnh sai tng th tt c cc loi tr o ca li trn h WGS-84 Quc t v h quy chiu Vit Nam; nh gi chnh xc to , cnh, phng v sau bnh sai; a ra gii php hp l chuyn to gia cc h thng ang s dng. Cho n nay tt c cc kin c nhn cng nh c quan u nht tr vi kt lun trn ca cng trnh.

III. QU TRNH O C LI KHNG CH TRC A QUC GIA VIT NAM

III.1 GIAI ON O C LI TAM GIC HNG I V II MIN BC

Mng li thin vn- trc a min Bc bao gm 1.035 im tam gic hng I v II to thnh mng li kiu dy c, trong c 339 im hng I, 696 im hng II, 13 cnh y, 28 im thin vn v 13 phng v Laplace. Cc tham s k thut ca li tam gic o gc hng I v hng II Min Bc nh sau: cnh hng I c chiu di trung bnh 25 km (cnh di nht l 42 km, cnh ngn nht l 9 km); khong cch gia cc ng y khong 130 km; o gc trong mng li c tin hnh bng my kinh v quang hc TT-2/6 v Wild T3 theo phng php t hp ton nhm; cc im hng II c b tr ch yu theo phng php chm li vo hng I; trong 13 cnh y c 7 cnh c o trc tip bng my o xa in quang, 6 cnh cn li c pht trin theo li ng y t ng y o bng thc dy invar; cc im thin vn c b tr ti hai u cnh y, c o bng cc my kinh v thin vn AY 2/10 v Wild-T4; cc tr o c chiu ln mt Ellipsoid quy chiu Krasowski, sau chiu ln mt phng chiu Gauss; tnh ton bnh sai c tin hnh trn mt phng Gauss, li hng I c chia thnh 3 khu c gi ph 2 hng im tnh ton bnh sai, mi khu c bnh sai ring theo phng php iu kin nhiu nhm Pranhis-Pranhevich; h thng to c xc nh trn c s tnh chuyn t im Ni Ng Lnh thuc li ca Trung Quc; m hnh Geoid phc v bnh sai c xy dng theo phng php o cao thin vn-trc a, gi tr cao Geoid t 27m n 39 m, trung bnh l 33m; li hng II c bnh sai theo phng php gin tip theo gc.

Mng li c o c t 1960-1964, tnh ton bnh sai xong nm 1966. Trn c s mng li ny Nh nc Vit nam cng b H to H Ni-1972. Nh vy H to H ni-1972 bao gm cc c trng sau:

Ellipsoid quy chiu Krasovski, mt chiu phng Gauss - Kruger;

im gc to c tnh chuyn t h thng ca Trung quc sang ti 1 im, li khng c nh v cht ch;

M hnh Geoid ca h thng ny c xy dng theo phng php thin vn - trc a, chnh xc khng cao, cha m bo cht lng cao trong x l ton hc, tnh ton lch dy di v d thng cao cha c s liu trng lc tham gia;

y khng khng phi l mt h quy chiu a phng ca mt quc gia m l h quy chiu cha c nh v cht ch trong h to ca cc nc x hi ch ngha c.

III.2 GIAI ON O C LI TAM GIC HNG I BNH -TR-THIN

Sau ngy thng nht t nc, t 1977-1983, Cc o c v Bn Nh nc giao nhim v cho Lin on o c i a tin hnh o c li tam gic hng I khu vc Bnh-Tr-Thin t v 16o10' n 17o10' ni tip li Thin vn-Trc a min Bc. Li gm 25 im, trong 3 im o trng vi li Thin vn-Trc a min Bc v 22 im mi c b tr nh l kho tam gic kp gia 2 cnh m rng c xc nh gc phng v Laplace, chiu di cnh t 20 km n 25 km, gc c o bng my kinh v Wild-T3. Cc ch tiu k thut ca li ny t nh li hng I min Bc.

III.3 GIAI ON O C LI TAM GIC HNG II MIN TRUNG

Nm 1983, vi s tham gia ca chuyn gia Lin x (c) Cc o c v Bn Nh nc quyt nh phng n xy dng mng li tam gic hng II dy c thay th cho vic xy dng mng li tam gic hng I dy c v chm li tam gic hng II. Tng s 351 im tam gic hng II c xy dng khu vc min Trung t v 10030 n 16o25. Chiu di cnh t 10-15 km, gc c o bng my kinh v Wild-T3 v OT-02. Sai s trung phng o gc tnh theo Pherer t c nh hn 100.

Li c o c t nm 1983 n 1989 theo 8 khu o: Khu Bnh-Tr -Thin n Bc Ngha Bnh (1983-1984); Khu Ngha Bnh (1984-1985); Khu Ngha Bnh-Ph khnh (1986); Khu Ph Khnh-Thun Hi (1987); Khu Thun Hi-Lm ng (1988); Khu c Lc-Lm ng (1989); Khu Gia Lai-Kon Tum (1990-1991); Khu ng Nai-Vng Tu (1992).

Li tam gic hng II min Trung c b tr 16 cnh y o bng my o xa in quang AGA-600 vi chnh xc mS/S