GELE Geodesy — Geodetic Control NetworksExam Answer Templates

Marks

1

Topic

Horizontal Control — Triangulation

Difficulty

easy

Template Id

T1

Examiner Tip

The single mark is for the complete concept: angles measured + baseline + Law of Sines. Any two of the three components without the third will likely receive 0 at strict marking.

Model Answer

Triangulation is a method of horizontal control surveying in which all the interior angles of a network of connected triangles are measured, together with at least one baseline distance, and the unknown side lengths are computed using the Law of Sines.

Question Type

very_short_answer

Answer Structure

• One complete sentence: name the method + what is measured (angles + baseline) + how unknowns are found (Law of Sines) [1 mark]

Scoring Breakdown

Common Mark Deductions

• Writing 'distances are measured' instead of 'angles are measured' — this describes trilateration, not triangulation
• Omitting the baseline — a triangle net without a baseline has no scale
• Vague answer such as 'a method using triangles' with no mention of what is measured

Key Phrases To Include

• angles of a network of triangles
• baseline
• Law of Sines
• horizontal control

Marks

1

Topic

Horizontal Control — Trilateration

Difficulty

easy

Template Id

T2

Examiner Tip

The examiner wants to see the contrast with triangulation — emphasize 'sides measured' vs. 'angles measured' to earn the mark cleanly.

Model Answer

Trilateration is a method of horizontal control surveying in which all the sides of a network of triangles are measured using electronic distance measurement (EDM), and the angles are computed from the measured distances. It is preferred when EDM equipment is available and angular measurements are difficult or time-consuming.

Question Type

very_short_answer

Answer Structure

• Part 1: Definition — sides measured by EDM, angles computed [½ mark conceptually]
• Part 2: One valid condition for preference [½ mark conceptually — awarded as a whole unit at 1 mark]

Scoring Breakdown

Common Mark Deductions

• Confusing trilateration (sides measured) with triangulation (angles measured)
• Omitting the EDM reference — modern trilateration is EDM-based
• Giving a condition that actually favors triangulation instead

Key Phrases To Include

• sides measured
• EDM (electronic distance measurement)
• angles are computed
• horizontal control

Marks

1

Topic

Orders of Accuracy — Control Hierarchy

Difficulty

easy

Template Id

T3

Examiner Tip

This is a classic board-exam concept question. The two key ideas are: direction (higher → lower order) and the prohibition (never lower → higher). State both for a complete answer.

Model Answer

Working from the whole to the part means that surveys always begin from higher-order control points (which have greater accuracy and wider spacing) and progressively densify to lower-order control points. Lower-order surveys are never used as the basis for extending higher-order control.

Question Type

very_short_answer

Answer Structure

• State the principle: higher-order → lower-order [1 mark]; the reverse prohibition is a bonus clarifier

Scoring Breakdown

Common Mark Deductions

• Describing it vaguely as 'starting from a big area' without mentioning order hierarchy
• Reversing the direction — saying lower-order is established first

Key Phrases To Include

• higher-order to lower-order
• densify
• never the reverse
• accuracy hierarchy

Marks

2

Topic

Triangulation — Law of Sines Computation

Difficulty

easy

Template Id

T4

Examiner Tip

The angle-sum check (Step 1) is a separate mark. Write it out even though it looks trivial — skipping it costs a mark. Always label which side is opposite which angle.

Model Answer

Given: AB = 6 500 m, ∠A = 62°, ∠B = 75° Step 1 — Find angle C: ∠C = 180° − 62° − 75° = 43° Step 2 — Apply the Law of Sines (BC is opposite ∠A): BC / sin A = AB / sin C BC = AB × (sin A / sin C) BC = 6 500 × (sin 62° / sin 43°) BC = 6 500 × (0.88295 / 0.68200) BC = 6 500 × 1.29464 BC ≈ 8 415 m

Question Type

numerical

Answer Structure

• Step 1: Compute angle C = 180° − A − B [1 mark]
• Step 2: Correct Law of Sines setup and final numerical answer with units [1 mark]

Scoring Breakdown

Common Mark Deductions

• Pairing BC with the wrong opposite angle (e.g., using sin B instead of sin A)
• Omitting the angle-sum step — examiner requires it explicitly
• Giving the answer without units (metres)

Key Phrases To Include

• ∠C = 180° − A − B
• BC / sin A = AB / sin C
• Law of Sines
• opposite angle

Marks

2

Topic

Vertical Control — Leveling Misclosure Tolerance

Difficulty

easy

Template Id

T5

Examiner Tip

Memorize T = k√K permanently. Board exams vary the values of k (4, 8, 12 mm) and K, but the formula never changes. Always convert K to km before substituting.

Model Answer

Given: K = 25 km, tolerance constant k = 8 mm/√km Formula: T = k√K Substitution: T = 8 × √25 T = 8 × 5 T = 40 mm The allowable misclosure for this leveling loop is 40 mm.

Question Type

numerical

Answer Structure

• State the formula T = k√K and identify the given values [1 mark]
• Correct substitution and final numerical answer in mm [1 mark]

Scoring Breakdown

Common Mark Deductions

• Using T = k × K (linear, not square root) — this is the most frequent error
• Using K in metres instead of kilometres — always check units before substituting
• Omitting units on the final answer

Key Phrases To Include

• T = k√K
• K in km
• tolerance
• misclosure

Marks

3

Topic

Horizontal Control Methods — Triangulation vs. Trilateration

Difficulty

medium

Template Id

T6

Examiner Tip

Structure your answer with numbered or bulleted points using the same category (measurements, computation, application) for both methods side-by-side. Parallel structure signals thoroughness.

Model Answer

Triangulation vs. Trilateration: 1. Field Measurements: • Triangulation: All interior angles of the triangle network are measured in the field. At least one baseline distance is also measured to provide scale to the network. • Trilateration: All sides of the triangle network are measured in the field using electronic distance measurement (EDM). No direct angular measurements are made. 2. Computational Procedure: • Triangulation: The unknown side lengths are computed using the Law of Sines: (side / sin opposite angle). Only angles are adjusted during network adjustment. • Trilateration: Angles are computed from the measured distances using the Law of Cosines: cos A = (b² + c² − a²) / (2bc). Only distances are adjusted during network adjustment. 3. Accuracy Consideration: • Triangulation is preferred in mountainous terrain where line-of-sight distances are long but angular measurements are still feasible with a theodolite. • Trilateration is preferred when precise EDM equipment is available and line clearance for distance measurement is practicable.

Question Type

short_answer

Answer Structure

• Point 1: Field measurements for each method (angles + baseline vs. all sides) [1 mark]
• Point 2: Computational method used (Law of Sines vs. Law of Cosines) [1 mark]
• Point 3: Condition of preference / accuracy context [1 mark]

Scoring Breakdown

Common Mark Deductions

• Stating 'triangulation uses distances' — this confuses the two methods
• Omitting the Law of Cosines for trilateration computation
• Writing a narrative that mixes the two methods without clear separation

Key Phrases To Include

• angles measured
• baseline
• Law of Sines
• all sides measured
• EDM
• Law of Cosines
• network adjustment

Marks

3

Topic

Triangulation — Strength of Figure

Difficulty

medium

Template Id

T7

Examiner Tip

Always connect the criterion (angle range) back to the mathematical reason (sine behavior). Examiners reward the cause-and-effect chain, not just a memorized number.

Model Answer

Strength of Figure in Triangulation: Definition: Strength of figure is a measure of how sensitively the computed side lengths in a triangulation network respond to errors in the measured angles. A network with high strength of figure produces large, reliable side values with minimal error amplification. Basis: When a side is computed by the Law of Sines (side = baseline × sin A / sin C), the accuracy of the result depends on the rate of change of the sine function at the angles used. Near 0° or 180°, sine changes rapidly for small angle changes, so a small angular measurement error causes a large error in the computed side. Near 90°, sine changes slowly, making the computation more stable. Well-Conditioned Triangle: A triangle is considered well-conditioned when all its interior angles fall within the range of approximately 30° to 120°. This range ensures that no angle has a dangerously small or near-180° sine value. Consequence of Weak Figure: A triangle with a very small angle (e.g., 5°) is a weak figure. Even a 1-second error in that angle can introduce a centimetre-level error in the computed side, degrading the overall accuracy of the control network.

Question Type

short_answer

Answer Structure

• Define strength of figure — error amplification concept [1 mark]
• Explain why sine function behavior at small angles causes weakness [1 mark]
• State the well-conditioned angular range 30°–120° and consequence of violating it [1 mark]

Scoring Breakdown

Common Mark Deductions

• Stating the range as 60°–90° only — this is too narrow and omits the full acceptable range
• Saying weak triangles are 'bad' without explaining the sine-function mechanism
• Omitting the definition and jumping straight to the range — losing the definition mark

Key Phrases To Include

• strength of figure
• error amplification
• sine function
• 30° to 120°
• well-conditioned
• Law of Sines

Marks

3

Topic

Triangulation — Extended Chain Computation

Difficulty

medium

Template Id

T8

Examiner Tip

In multi-triangle problems, always explicitly label which angle is opposite which side before writing the ratio. This prevents the most common pairing error.

Model Answer

Given: PQ = 10 200 m, ∠P = 55°, ∠Q = 68° (in △PQR); ∠Q' = 48°, ∠S = 65° (in △QRS) Part (a) — Compute QR: Step 1: ∠R (in △PQR) = 180° − 55° − 68° = 57° Step 2: QR is opposite ∠P; PQ is opposite ∠R QR / sin P = PQ / sin R QR = PQ × (sin P / sin R) QR = 10 200 × (sin 55° / sin 57°) QR = 10 200 × (0.81915 / 0.83867) QR = 10 200 × 0.97672 QR ≈ 9 963 m Part (b) — Compute RS using QR as new baseline: Step 1: ∠R' (in △QRS) = 180° − 48° − 65° = 67° Step 2: RS is opposite ∠Q'; QR is opposite ∠S RS / sin Q' = QR / sin S RS = QR × (sin Q' / sin S) RS = 9 963 × (sin 48° / sin 65°) RS = 9 963 × (0.74314 / 0.90631) RS = 9 963 × 0.81994 RS ≈ 8 169 m

Question Type

numerical

Answer Structure

• Part (a) Step 1: Angle sum check for △PQR, find ∠R [½ mark]
• Part (a) Step 2: Correct Law of Sines for QR, numerical answer [1 mark]
• Part (b) Step 1: Angle sum check for △QRS, find ∠R' [½ mark]
• Part (b) Step 2: Correct Law of Sines for RS using QR, numerical answer [1 mark]

Scoring Breakdown

Common Mark Deductions

• Carrying an uncorrected angle into Part (b) — errors propagate, losing both marks
• Wrong opposite angle pairing (QR opposite ∠Q instead of ∠P)
• Not identifying QR as the baseline for the second triangle

Key Phrases To Include

• 180° − angles = third angle
• opposite angle pairing
• Law of Sines
• new baseline

Marks

3

Topic

Triangulation — Strength of Figure Assessment

Difficulty

medium

Template Id

T9

Examiner Tip

For 'comment on suitability' questions, use a three-part structure: (1) criterion check, (2) mathematical reason, (3) conclusion with recommendation. This ensures you address all marking points.

Model Answer

Assessment of Suitability: This triangle is unsuitable as a triangulation figure for the following reasons: 1. Violation of Well-Conditioned Range: Two of the three angles (15° and 20°) fall below the minimum recommended angle of 30° for a well-conditioned triangulation figure. Only angles in the range 30°–120° produce reliable computed sides. 2. Sine Function Sensitivity at Small Angles: • sin 15° = 0.2588 and sin 20° = 0.3420 — both small values. • At these small angles, the sine function changes rapidly; a 1-second error in the 15° angle produces a much larger proportional change in sin 15° than the same 1-second error near 60°. • By the Law of Sines, the computed side = baseline × (sin small angle / sin opposite angle), so the error in the numerator is disproportionately large. 3. Elongated Shape: The 145° angle produces a very flat, elongated triangle. The side opposite 145° (the largest side) is well-determined, but the two short sides opposite 15° and 20° are very poorly determined. Conclusion: All three angles violate the 30°–120° range criterion. This triangle has very poor strength of figure and should be redesigned with better-conditioned angles.

Question Type

short_answer

Answer Structure

• Identify violation of the 30°–120° range criterion [1 mark]
• Explain the sine function sensitivity mechanism at small angles [1 mark]
• Describe the physical/geometric consequence (elongated shape, poor side determination) [1 mark]

Scoring Breakdown

Common Mark Deductions

• Simply saying 'the triangle is weak' without explaining why (no mechanism = no mark)
• Only mentioning the two small angles without discussing the 145° angle
• Not making a conclusion or recommendation

Key Phrases To Include

• well-conditioned range 30°–120°
• sine function changes rapidly
• strength of figure
• error amplification
• Law of Sines

Marks

3

Topic

Horizontal Control — Classification of Methods

Difficulty

easy

Template Id

T10

Examiner Tip

Number each method clearly and maintain the same structure for each (name → measurement → brief description). Examiners match your answer against a key — parallel structure helps them award every mark you earned.

Model Answer

Three Primary Methods of Horizontal Control: 1. Triangulation: Primary field measurement: All interior angles of a network of triangles, plus at least one measured baseline. Description: A series of connected triangles are formed across the survey area. The angles of each triangle are measured precisely with a theodolite, and the unknown sides are computed using the Law of Sines. 2. Trilateration: Primary field measurement: All side lengths of the triangle network, measured by electronic distance measurement (EDM). Description: Instead of angles, all distances are measured directly. Triangle angles are then computed using the Law of Cosines. This became prominent with the development of precision EDM instruments. 3. Traverse: Primary field measurement: Horizontal angles (or directions) at each traverse station AND the distance of each traverse leg. Description: A series of connected lines is run through the survey area, with both the direction and length of each line measured. Traverses may be open (between two known control points) or closed (looping back to the starting point or closing on a known point).

Question Type

short_answer

Answer Structure

• Method 1 — Triangulation: name + primary measurement (angles + baseline) + brief description [1 mark]
• Method 2 — Trilateration: name + primary measurement (all distances by EDM) + brief description [1 mark]
• Method 3 — Traverse: name + primary measurement (angles AND distances) + brief description [1 mark]

Scoring Breakdown

Common Mark Deductions

• Stating that traverse measures only directions without distances (or vice versa) — both are required
• Listing GNSS as one of the three classical methods without describing the three traditional methods
• Describing all three methods in one combined paragraph making it unclear which is which

Key Phrases To Include

• triangulation
• trilateration
• traverse
• angles
• baseline
• EDM
• Law of Sines
• Law of Cosines

Marks

5

Topic

Orders of Accuracy — Philippine Context

Difficulty

hard

Template Id

T11

Examiner Tip

Five-mark questions are marked against a point-by-point breakdown. Structure your answer with clear part labels (a), (b), (c), (d) matching the question. Never write a single continuous paragraph for a 5-mark question — subdivided answers let the examiner award every mark you earned.

Model Answer

Classification of Geodetic Control Networks by Order of Accuracy (a) General Hierarchy: Geodetic control networks in the Philippines are classified into orders of decreasing accuracy: • First Order (Geodetic): Highest precision; forms the national primary framework. Spacing: 100–300 km (horizontal); used for crustal deformation monitoring, national mapping datum. • Second Order (Class I and II): Secondary framework densifying First Order; spacing 20–50 km. Sufficient for state/regional mapping and major engineering projects. • Third Order: Local control for cadastral surveys, engineering, and construction projects. Spacing 2–10 km. Each lower order is established by measurements made relative to the immediately superior order, never independently. (b) Principle of Extension (Whole to Part): The cardinal principle is: control networks are always densified from a higher order to a lower order — from the whole to the part. A Third Order point is established by measuring from Second Order points; a Second Order point is established from First Order points. It is never permissible to extend a higher-order network from lower-order monuments because the accumulated errors of the lower-order points would corrupt the higher-order framework. This also ensures national consistency and traceability. (c) Leveling Misclosure Tolerances by Order: Precision leveling is used to establish vertical control benchmarks. The allowable misclosure T for a leveling circuit is computed as: T = k√K where K = total loop distance in kilometres and k is an order-dependent constant: • First Order, Class I: k = 4 mm • First Order, Class II: k = 6 mm • Second Order: k = 8 mm • Third Order: k = 12 mm For example, a Second Order loop of 16 km has an allowable misclosure of: T = 8√16 = 8 × 4 = 32 mm. If the actual misclosure exceeds T, the leveling run must be repeated. (d) Role of NAMRIA in the Philippine Context: The National Mapping and Resource Information Authority (NAMRIA), under the Department of Environment and Natural Resources (DENR), is the central mapping agency of the Republic of the Philippines. NAMRIA: • Maintains and publishes the Philippine Reference System of 1992 (PRS92), which is the official horizontal datum tied to WGS84. • Publishes the Philippine Vertical Datum (mean sea level at Intramuros tide gauge) as the national height reference. • Classifies, maintains, and publishes the national geodetic control network monuments. • Issues certificates of geodetic control data to licensed geodetic engineers for survey tie-in, as required by RA 8560 (Geodetic Engineers Act) and PD 1529 (Property Registration Decree). • Coordinates with the PPCP (Philippine Persistent CORS Project) for GNSS-based active control network densification.

Question Type

long_answer

Answer Structure

• Part (a): Hierarchy with three orders named, brief description of each, and spacing/use [1 mark]
• Part (b): Whole-to-part principle explained with direction and prohibition stated [1 mark]
• Part (c): Formula T = k√K stated and applied with correct k values for at least two orders [1.5 marks]
• Part (d): NAMRIA role — PRS92, datum, control network, RA 8560/PD 1529 reference [1.5 marks]

Scoring Breakdown

Common Mark Deductions

• Omitting the worked numerical example for the tolerance formula — examiners expect application, not just the formula
• Mentioning NAMRIA without specifying its role in PRS92 or the national control network
• Not referencing any Philippine law — this is a PRC board exam; legal references earn marks
• Describing the hierarchy in reverse order (Third → First) showing conceptual confusion

Key Phrases To Include

• First Order
• Second Order
• Third Order
• whole to the part
• T = k√K
• NAMRIA
• PRS92
• WGS84
• RA 8560
• PD 1529
• densification

Marks

5

Topic

Triangulation — Extended Chain with DMS Angles

Difficulty

hard

Template Id

T12

Examiner Tip

DMS-to-decimal conversion is a hidden mark trap. Write the conversion explicitly: 63°15' = 63 + 15/60 = 63.25°. Examiners see this and know you understand the process. Skipping it suggests guessing.

Model Answer

Given: AB = 12 400 m △ABC: ∠A = 48°30', ∠B = 63°15' △ACD: ∠A = 37°45', ∠C = 72°20' Part (a) — Compute AC (in △ABC): Step 1: ∠C = 180°00' − 48°30' − 63°15' = 68°15' Step 2: AC is opposite ∠B; AB is opposite ∠C AC / sin B = AB / sin C AC = 12 400 × (sin 63°15' / sin 68°15') sin 63°15' = sin(63 + 15/60)° = sin 63.25° = 0.89253 sin 68°15' = sin(68 + 15/60)° = sin 68.25° = 0.92978 AC = 12 400 × (0.89253 / 0.92978) AC = 12 400 × 0.95994 AC ≈ 11 903 m Part (b) — Compute CD (in △ACD, using AC = 11 903 m as new baseline): Step 1: ∠D = 180°00' − 37°45' − 72°20' = 69°55' Step 2: CD is opposite ∠A; AC is opposite ∠D CD / sin A = AC / sin D CD = 11 903 × (sin 37°45' / sin 69°55') sin 37°45' = sin 37.75° = 0.61280 sin 69°55' = sin 69.917° = 0.93906 CD = 11 903 × (0.61280 / 0.93906) CD = 11 903 × 0.65256 CD ≈ 7 767 m Part (c) — Assessment of triangle ACD: Angles: ∠A = 37°45' (37.75°), ∠C = 72°20' (72.33°), ∠D = 69°55' (69.92°) All three angles fall within the well-conditioned range of 30°–120°. Verdict: Triangle ACD is well-conditioned. No angle is below 30° or above 120°, ensuring reliable Law of Sines computation with minimal error amplification. The figure has good strength of figure.

Question Type

numerical

Answer Structure

• Part (a) Step 1: ∠C = 68°15' by angle sum [½ mark]
• Part (a) Step 2: Correct Law of Sines, AC ≈ 11 903 m with units [1 mark]
• Part (b) Step 1: ∠D = 69°55' by angle sum [½ mark]
• Part (b) Step 2: Correct Law of Sines using AC as new baseline, CD ≈ 7 767 m [1 mark]
• Part (c): Check all three angles against 30°–120° range, explicit verdict [1 mark — accept reasonable computed values ± rounding]

Scoring Breakdown

Common Mark Deductions

• Not converting DMS to decimal degrees before computing sine values — major source of error
• Using the wrong opposite angle (e.g., pairing AC opposite ∠A instead of ∠B in △ABC)
• Not clearly stating that AC becomes the new baseline for the second triangle
• Assessing only one or two angles for well-conditioned criterion instead of all three
• Rounding errors from premature truncation of sine values — carry at least 5 decimal places

Key Phrases To Include

• angle sum = 180°
• DMS to decimal conversion
• opposite angle pairing
• new baseline
• well-conditioned
• 30°–120°
• strength of figure

Marks

2

Topic

Triangulation — Role of the Baseline

Difficulty

medium

Template Id

T13

Examiner Tip

The second mark is specifically for the error propagation argument. Make this mechanism explicit: 'All computed sides inherit the baseline error because they are computed as ratios involving the baseline.'

Model Answer

Role of the Baseline: The baseline is the only directly measured distance in a classical triangulation survey. It provides the scale of the entire network — without it, only the shape (angles) of the triangles is known but no actual distances can be computed. All computed sides in the network ultimately derive their length from the ratio with the baseline via the Law of Sines. Why Maximum Precision is Required: Because all other distances in the network are computed as proportional multiples of the baseline, any error in the baseline length propagates into EVERY computed side in the network. A 1-part-per-million (1 ppm) error in the baseline introduces a 1 ppm systematic error in all derived distances throughout the chain. Since the baseline error cannot be removed by angular adjustment, it must be minimized at the source by using precision tapes (invar tapes with tension and temperature corrections) or modern precise EDM with atmospheric corrections.

Question Type

short_answer

Answer Structure

• Part 1: Role — baseline provides scale; all computed sides derive from it via Law of Sines [1 mark]
• Part 2: Reason for precision — baseline error propagates to ALL computed sides; cannot be removed by adjustment [1 mark]

Scoring Breakdown

Common Mark Deductions

• Saying 'the baseline is important for accuracy' without explaining the propagation mechanism
• Confusing the baseline with a traverse leg — baseline is specifically for triangulation scale
• Not mentioning that angular adjustment cannot correct baseline errors

Key Phrases To Include

• scale of the network
• only directly measured distance
• Law of Sines
• error propagates
• all computed sides
• invar tape
• ppm

Marks

2

Topic

Vertical Control — Leveling Tolerance by Order

Difficulty

easy

Template Id

T14

Examiner Tip

Always write the verdict explicitly: 'Since [observed] < [tolerance], the run is ACCEPTABLE.' Examiners will not infer this from numbers alone — the stated conclusion earns the mark.

Model Answer

Formula: T = k√K where K = loop distance in km, k = 4 mm (First Order, Class I) Computation: T = 4 × √36 T = 4 × 6 T = 24 mm Acceptability Check: Observed misclosure = 18 mm Allowable tolerance T = 24 mm Since 18 mm < 24 mm, the observed misclosure is ACCEPTABLE. The leveling run meets First Order, Class I precision.

Question Type

numerical

Answer Structure

• State T = k√K with k = 4 mm for First Order Class I [½ mark]
• Compute T = 24 mm correctly [½ mark]
• Compare 18 mm vs. 24 mm and make an explicit verdict [1 mark]

Scoring Breakdown

Common Mark Deductions

• Using k = 8 mm (Second Order) for a First Order question
• Computing T = 4 × 36 = 144 mm (forgetting the square root)
• Failing to state the acceptability verdict — the comparison is worth a full mark

Key Phrases To Include

• T = k√K
• k = 4 mm
• First Order Class I
• T = 24 mm
• 18 mm < 24 mm
• acceptable

Marks

2

Topic

Philippine Geodetic Law — Control Network Requirements

Difficulty

medium

Template Id

T15

Examiner Tip

Board exams regularly test knowledge of Philippine geodetic legislation. Always connect the law to the specific technical requirement it mandates. 'PD 1529 requires tie-in' earns a mark; 'a law requires tie-in' earns nothing.

Model Answer

Cadastral and land registration surveys in the Philippines must be tied to the national geodetic control network for two principal reasons: 1. Legal Requirement and Survey Accuracy: Under Presidential Decree No. 1529 (Property Registration Decree), all surveys submitted for land registration must comply with Bureau of Lands (now DENR-LMB) technical standards. Tie-in to NAMRIA-published geodetic control ensures that parcel boundaries are uniquely and unambiguously positioned within the national coordinate reference system (PRS92/PPCS), preventing overlapping claims and positional discrepancies. 2. Professional Standards and Responsibility: Under Republic Act No. 8560 (Philippine Geodetic Engineering Act of 1998), it is the duty of a licensed geodetic engineer to perform surveys in accordance with technical and professional standards. Using the national geodetic control network ensures traceability of all measurements to a common datum (PRS92), which is a fundamental requirement of professional geodetic practice. Failure to tie-in to the control network is a basis for disapproval of the survey by DENR-LMB.

Question Type

short_answer

Answer Structure

• Legal requirement — PD 1529 reference with explanation of purpose (unique parcel positioning, PRS92) [1 mark]
• Professional standard — RA 8560 reference with explanation of geodetic engineer's duty and datum traceability [1 mark]

Scoring Breakdown

Common Mark Deductions

• Mentioning laws by number only without explaining their relevance to the control tie-in requirement
• Citing CA 141 (Public Land Act) as the primary law — while relevant, PD 1529 and RA 8560 are more directly applicable here
• General answer about 'accuracy' without connecting to the legal mandate

Key Phrases To Include

• PD 1529
• Property Registration Decree
• RA 8560
• Geodetic Engineering Act
• PRS92
• NAMRIA
• datum traceability
• DENR-LMB