DGPS Survey

DGPS SRVEY OF FOREST BLOCKS -MYTHS AND REALITIES

(By Dr HC MISHRA, IFS RTD, Secretary PEF)

 

ABSTRACT- There is a dispute between forest and Revenue boundaries almost all over the country. Both Forest and Revenue departments have old maps which are crude, approximate, made separately at different  times by different surveyors using different survey instruments with different accuracies and least counts plotted manually on paper , without projection concept of GIS ,which are mostly squeezed now altering the original dimensions. This was done at a time when land value was negligible decades back and so are indicative. The magnetic bearings of old Forest blocks are altered now due to changing  Declinations and Horizontal Distances were not taken precisely . The description based maps of Forest Blocks suffer from the defect that the original streams , rivers, roads, canals, hillocks have altered ground positions at many places. Double surveying of a single line has created further complications as Revenue villages are sometimes assigned survey numbers after FBs are notified and situation is more complex when boundary pillars are missing  and displaced. These are resulting in demarcation of Forest Blocks and if demarcated the Revenue department maps don’t tally with it. The Author who has experience of many DGPS surveys in AP and Telangana states tries to explain the complexities in simple nontechnical language and proposes a solution to the Re fixation of Forest Boundaries and a unified Revenue Forest map.

INTRODUCTION- DGPS stands for Differential Global Positioning System, which was based on instruments getting signals from US satellites called Navstars. Now countries like Russia, European Union, China, India etc have sent their satellites sending signals and modern positional systems accept signals from all satellites of the above countries and they are called DGNSS ( Differential Global Navigation Satellite Systems). DGPS is almost outdated now and all machines are DGNSS only. A single machine is usually called GPS which is called GNSS now. 

GPS (now called GNSS)  is an instrument which receives signals from certain satellites and gives us four things only. They are Latitude , Longitude, Height  above sea  level and Time ( of observation). As lat-longs of a point is unique on earth surface, these things are used (mostly the first three ) to create maps of the points , lines , polygons surveyed and the area, perimeters etc by proprietary software of the instrument manufacturers or GIS Software. By taking a large concentration of points we can  even create a three Dimensional map of the polygons by proprietary or GIS software by interpolations. Differential GPS implies that ordinarily two instruments are used for removal of error of the position.

WHAT IS A DGPS (DGNSS)
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 It is an instrument which receives signals from certain satellites and gives us four things only. They are Latitude , Longitude, Height  above sea  level and Time ( of observation ).
     These four things are used (mostly the first three ) to create maps of the points , lines , polygons surveyed and the area, perimeters etc by proprietary software of the instrument manufacturers or GIS Software. By taking a large concentration of points we can  even create a three Dimensional map of the polygons by proprietary or GIS software by interpolations.

HISTORY OF FOREST BLOCKS-
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Forest Blocks were notified  since 1865 onwards with descriptions or magnetic bearing  and distance between pillars . THERE WERE PILLARS ON GROUND & FORESTERS USED TO MAINTAIN THE BOUNDARY WITHOUT GPS SETS, which came to India  after 1990.
   But MOST PLACES FORESTERS COULD NOT MAINTAIN  THE NOTIFIED PILLARS AND LINES APPROVED BY GOVT. OFTEN THERE ARE NO PILLARS AND IF PILLARS ARE THERE THEY ARE AT POSITIONS DIFFERENT FROM NOTIFICATIONS. Had it been maintained the DGPS SURVEY of old pillars / lines was Possible without any problem & manipulations & perhaps disputes.
    THE FOREST BLOCKS ARE usually on hilly tracks to great extent or on undulating terrain. They are ISLANDS WITHIN REVENUE LANDS & other lands and the existing maps of FBs are very crude, approximate, inaccurate, indicative with approximate shapes and  area statement. These maps have incorrect orientation to Magnetic/ True north, approximate angles and old magnetic bearings  ( magnetic bearings have changed over years due to changing declination ) , wrong lengths of polygon sides often not giving correct horizontal measurements, inaccurate plotting.

PROBLEMS OF ADJOINING REVENUE MAPS- 
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The adjoining maps of adjoining Revenue lands to our FBs also have similar errors . This is also the reason why both maps cant be joined physically on a plain paper or on a computer screen   after scanning without gaps and overlapping.There are mstakesin shape and size of internal polygons inside FBs showing enclosed revenue lands or dis reserved lands whenever they exist. .
  NO TECHNICAL PROCEDURE ( EVEN GEO REFERENCING OF SCANNED FB MAPS ) CAN RECTIFY THE ERRORS OF A  DIRTY MAP (contrary to perception of  nontechnical persons )WITH ERRORS ALAROUND .THIS IS THE REASON WHY BOTH MAPS CANT  BE  JOINED PHYSICALLY   ON A PLAIN PAPER  OR ON A COMPUTER SCREEN AFTER SCANNING WITHOUT GAPS AND OVERLAPPINGS BETWEEN FOREST MAPS AND REVENUE MAPS.

REASONS FOR MISMATCH BETWEEN REVENUE & FOREST MAPS
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   The main reason of mismatch between the revenue and FB maps is as follows.
A- Both  MAPS PREPARED INDEPENDENTLY BY DIFFERENT PEOPLE, at different periods, 
B-.They are prepared by different crude instrument with different least counts and accuracies .
C- THE LENGTHS OF LINES don’t give the correct horizontal distances AND BEARINGS / ANGLES are not precise and change with changing Declinations.
D- The natural features like streams , rivers, roads  etc have changed on ground with Efflux of time.
E- Maps are manually plotted and areas manually derived incorporating errors etc.

   DGPS SURVEY MISCONCEPTIONS-
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 1- DGPS survey of our old  forest blocks ( FB) alone is a solution to our boundary problems with adjoining revenue and private lands.
2-After DGPS survey , the shape of the new computer generated forest block maps will tally precisely with our old FB maps and so also the areas will tally.
3- we need to supply the old FB blocks to DGPS surveyors  and GIS scientists , who in turn will give us an indisputable block map to be acceptable to all stake holders.
4- It is duty &  responsibility of DGPS SURVEYORS TO DECIDE THE FOREST BOUNDARY BASED ON SUPPLIED OLD FB MAP & DGPS INSTRUMENT.
5- If we can provide budget, Forest Departments can solve the boundary problems of old FBs by DGPS survey.
6- USE OF LATEST SURVEY TECHNOLOGY ALONE WILL GIVE US THE SOLUTION TO OUR BOUNDARY PROBLEMS AND DISPUTES of old FBs.

7. There is a final misconception that lat-long will be eternally constant on earth surface though its change is very slow. In fact India was in Southern hemisphere once few million years back and earth plates are slowly and continuously moving, the Australian plate moving the fastest requiring quicker re fixation  of lat-longs.
   These are all misconceived  thinking without understanding the problems.


REFIXATION OF Forest Block (FB)  Boundary  WHEN PILLARS & LINES ARE NOT AVAILABLE-.
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 There were two ways blocks were notified . One way was by Magnetic bearing and horizontal distance between pillars and second was by description with respect to village survey numbers and natural boundaries like streams , hills, roads etc each type accompanied by a crude map.
   The first type of FBs can’t be easily and accurately demarcated on ground from first pillar  because the magnetic bearings are altered over the years and secondly the angles and distances are mostly inaccurate resulting in displacement of later pillars.
   The second type are also difficult as streams, rivers, roads etc have changed positions and village survey numbers are altered & so also FB lines and further associated revenue maps are crude & manipulated sometime.

WHAT GIS SCIENTISTS DO TO MATCH THE TWO MAPS-
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    The best way to make a GPS survey of  FBs is to follow the MARK & MEASURE principle. However as pillars are missing on ground quite often and refixing the pillars have difficulties in hilly terrains, this method of mark & measure is rarely applied.

  The onus of demarcation is sifted from field staff to GIS scientists as a result and innocent and ignorant scientists without much knowledge of the problems take up the task. this Geo referencing after scanning is resorted to everywhere now as there are practically no Filed staff who like even going to Forests and can fix pillars in difficult hilly terrains camping there for days together.  The GIS scientists are provided with the old FB crude maps which are mostly squeezed in dimension over decades and are not precise. The said maps are scanned in 300 to 600 dpi scanners and geo referenced taking lat-longs of suitable points on the ground and assigning them to corresponding points on scanned maps in GIS software. But this does not correct all the details of irregular and defective map, which still remains after geo referencing . The gaps and over lapping when geo referenced village and FB Maps are merged/overlaid are often beyond tolerance limit and go to hundreds of meters sometimes. The GIS scientists with Forest Field staff adjust the maps by editing using their discretions and merge double lines into one sometime without Authority and without understanding the legal complexities. The Author has come across cases when some cunning and mischievous scientists in collusion with field staff edit the lines to suit vested interests sometimes under Temptations.
DISPUTES BWTWEEN FOREST DEPT & REVENUE DEPT
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  But this does not solve the problem. The big  FBs after geo referencing get a  different shape and different area than notified and when the lines are re-laid  on ground based on geo referenced maps , both Forest and Revenue staff disagree and disown. This is the problem in most areas and most cases. When the FB pillars and lines get  lat- longs after geo referencing , many officers say that it is not notified by Govt and so not valid.
THE SOLUTIONs-
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  The solution lies in a MARK AND MEASURE PRINCIPLE , marking the boundary being first attempted by revenue & forest department jointly. When pillars could be maintained without GPS till 1990, it should be possible to demarcate them now to a great extent. However Foresters are avoiding this now and putting the responsibility of  the work on the GIS wing completely , which is wrong. If scanning & geo referencing is resorted , govt should issue orders first notifying a Standard Operating Procedure (SOP) , where in certain FB area differences after DGPS survey need be ignored and such instructions need be followed by departments. It is understood that Govt of Odisha has notified a SOP for fixing FB-Revenue boundary and it may be examined and followed.

 My personal feeling is that Forest Department need be liberal to ignore areas which are under cultivation since long along boundaries restricting the Forest Blocks with vegetation and demarcate existing Forest Lines more sincerely , rather than taking the FB line along encroachment with no practical benefit. All recent reservations and dis reservation need be by lat-longs which are permissible under Forest Act existing now.

 

 

   

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