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How-to Create a Geoid or Vertical Offset Model (VOM)

This How-to describes step-by-step how to create your own geoid model file or height level correction model and use it within Qinsy.

See Questions & Answers for more in formation.
Also for items with an asterisk *.

Related pages:

Geoid model decision chart

Questions & Answers

SubjectQuestionAnswer
ProjectedWhat is projected data?We assume that this is projected on project datum and the separation value is also relative to project datum.
Point spacing

What is regular and irregular spacing?

Irregularly spaced:

Regularly spaced:

What is meant by having a different spacing in x and y?The data can be regularly spaced but still have a different spacing in X and Y.
Area sizeWhat is a small area?

This is a bit tricky since it mostly depends on points in an area:

  • If you have an ASCII file that covers the whole continent or more, for example, it is recommended to use the BIN workflow.
  • If it just covers your work site, using a QGFVOM is recommended.

If the QGFVOM is larger than 15MB it is also a good indication that you might need to use either a smaller area or try the BIN workflow.

DatumWhat is Project datum and Source datum?

Example of geodetic setup:

Project datum: ED50
Source datum: WGS 84

Purple steps

What do they refer to?

Storage locations

Were are the different types of geoid model files stored?
SourceTypeFormatFile LocationAdditional information
QPS installersGeoid ModelsBINC:\Program Files (x86)\Common Files\QPS\Geo\GeoidAll (pre-defined) Geoid BIN files installed by Qinsy
using the separate QPS Geodetic Package 3.0.x installer
Created by userGeoid ModelsBINC:\Users\Public\Public Documents\QPS\Shared\Geo\Geoid

Geoid BIN files (Lat/Long and E/N),
Created from a Sounding Grid exported as Geoid Model

Vertical Offset ModelsQGFvomProject folder\Geoid

Vertical Offset Models (VOM) in *.qgfvom format as created in the Survey Manager

Previously: River Line Model and VORF models in PRO format

QGFVOM VS BIN

What is the advantage of one format over the other?

QGFVOMBIN
Used in all QPS software(tick)(tick)
Use for large areas(error)(tick)
Irregularly spaced points(tick)(error)
Regularly spaced points(tick)(tick)
Datum (ellipsoid) aware(error)(tick)