SurveyStar LDP Thailand

Prajuab Riabroy

About this app

SurveyStar LDP Thailand converts coordinates between a Low Distortion Projection (LDP) and the reference datums surveyors in Thailand and Southeast Asia work with every day — on site, on your phone.

An LDP keeps grid distances close to ground distances across a project area, which UTM cannot do: its distortion can reach hundreds of parts per million, enough that setting-out distances no longer match the ground. This app is the tool that puts an LDP to work once it exists.

THAILAND LDP (TH-LDP) BUILT IN
All 83 provincial zones from the 2026 EIT proposal ship with the app — 70 Transverse Mercator and 13 Lambert Conformal Conic (1SP). Pick your province and the projection is ready: central meridian, latitude of origin, scale factor and false easting/northing all filled in. Each zone shows its CM/CP, terrain height range and mean combined scale factor, so you know what you are working with before you use it.

DEFINE YOUR OWN PROJECTION
Working to a departmental or project CRS instead? Build a Transverse Mercator or 1SP Lambert definition of your own, with validation that catches the mistakes that matter. Angles accept plain decimal degrees or the spaced DMS you actually type — 17 25 30 — and tidy themselves into 17°25'30.00" when you move on. Save definitions to reuse, edit them when a value needs correcting, and share them with your team.

TRANSFORM IN BOTH DIRECTIONS
Enter northing and easting in your LDP and read the result in the destination datum, or work the other way. Every transformation reports what a surveyor needs alongside the coordinates:

• Grid scale factor for both sides
• Grid convergence for both sides
• Geoid height, from the TGM2017 geoid model for Thailand

Reference datums cover Thailand, Laos, the Philippines, Bangladesh, Myanmar, Vietnam and Singapore — geographic and UTM — with the transformation done by the PROJ library, the same engine behind professional GIS software.

SEE IT ON A MAP
Plot the transformed point on OpenStreetMap or a topographic layer with contours and terrain. When you are using a TH-LDP province, the map draws the zone's extent, so you can see at a glance whether your point falls inside the area the projection was designed for.

TAKE THE RESULT WITH YOU
Export the transformation as PDF for a record, or as CSV, Excel or plain text for your own processing. Numbers go into Excel as numbers, ready to compute with.

TAKE THE PROJECTION WITH YOU
Send a coordinate system to the equipment that needs it:

• Trimble JobXML (.jxl) — imports into CHCNav LandStar and other controllers that read JobXML
• JSON — the SurveyStar LDP Companion format, so definitions move between the two apps

Export one zone or your whole saved set at once.

BUILT FOR THE FIELD
Coordinate transformation, the geoid model and every LDP zone work without a connection; only the map layers need one. Light and dark themes, and a Thai or English interface.

WHO IT IS FOR
Land surveyors, engineering and construction surveyors, cadastral surveyors and GIS professionals — anyone who has to move coordinates between a local projection and a national datum and be sure of the answer.

SURVEYSTAR LDP COMPANION
Designing a new LDP rather than using one? SurveyStar LDP Companion computes the scale factor, builds the definition and analyses distortion against real points. Definitions pass between the two apps as JSON.

This is a calculation tool. Always check results against a known control point before relying on them for setting out or cadastral work.

What’s new

Quick TM is now SurveyStar LDP Thailand. Same app, same data: your saved
projections and settings carry over untouched.

Working outside Thailand? This app's zones, geoid model and datums cover
Thailand and Southeast Asia only. Install SurveyStar LDP Companion instead -
it builds a Low Distortion Projection for any location on earth.

This release also updates the libraries the app runs on. Nothing changes in
how you use it.