Optimizing GPS accuracy

Bence Sprok

16/08/2009 - Miskolc

Why and when shall we use GPS?

- Shall not be used for sprint maps

- Useful when no base map is available

- Or only aerial photo is present

- Early phase – creating base map, polygons

- Might not be fast for later processes

What kind of unit? - “Hobby” type will be fine - We don't need professional units (cost 5000 €<)

- At least 2, but preferably 3-4 different ones

- High sensitive receiver (SiRF III< , MTK, etc.)

- External antenna is highly recommended - Forget the “built-in” types (Forerunner and others) and the car navigation systems - Look for the trackpoint memory

~350 € ~20 €

~60 € ~60 € ~60 €

How to use? - All GPS work simultaneously

- Use distance based recording (~3m) instead of time interval, if possible. - Along with the “analog” accessories (board, pen, notes)

- Try to keep them as high as possible(special cap, backpack)

- Try to plan your work according to the satellites' positions

- One track is not a track. Try to track main features more than once in different time period.

- Use waypoints

- Download your work with your favourite program - Edit it - erase unnecessary parts

- Filter it if you used time interval method

- Convert it to .gpx formatIf needed, use gpsbabel to do that

- Transform from WGS'84 to the desired projectionMy suggestion is GlobalMapper

- GlobalMapper supports any kind of projection(OCAD supports only the most commonly used)

- Watch for the map datum and projection(according to your source)

- Bearing must not distort

(it's a must for any kind of topographic map)

Why do we need GlobalMapper if OCAD is

present?

Magnetic declination - Orienteering maps represent magnetic North

- Calculate the declination online

http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp

Advantages-

Disadvantages

+ Saving time+ Better accuracy in certain cases+ Reference aerial photos (GM/OCAD)+ Combine mapmakers’s work

- Pine forest, deep valleys - Height (z-level) data - More work for preparing - Costs?

Questions?

Wake up!Lunch time!