Wilbur is great basic terrain height map editing tool to create ArmA 2 terrains.

1. Filter → Noise → Fractal Noise, ridged multifractal, operation: replace, H: 1, amplitude: 1, lacunarity: 1.9, displacement: -10, octaves: 7, XY scale: 2 and other box 2, offset: 1, XY origin: -10 and other box -10, fgain: 2, seed: click random button
2. Filter → Fill → Fill Basins (CTRL-B), use default -1 value
3. Filter → Mathematical → Span, Low = -60, High = 1000
4. Filter → Noise → Percentage Noise, 5% (5% is very very rough, too rough! suggest you try smaller values or add some blur later)
5. Filter → Fill → Fill Basins (CTRL-B), use default -1 value
6. Choose incise flow or fluvial erosion first pass, see below
7. Filter → Fill → Fill Basins (CTRL-B), use default -1 value
8. Choose incise flow or fluvial erosion second pass, see below

That makes quite nice looking eroded terrain.

Filter → Erosion → Incise Flow, use values for first pass:
blur 2
amount 3.5
flow exponent 0.35
effect blend 0.25

Second pass:
blur 0.5
amount 2
flow exponent 0.1
effect blend 0.1

Wilbur sports a fluvial erosion model in addition to the incise flow operation. Incise flow requires a connected drainage system for best effect. The fluvial erosion system works either way. Wilbur uses a fluvial erosion model based on the precipitin or waterbot models. It randomly drops an agent onto the surface and that agent travels downhill, moving altitude from the higher cell to the lowest one adjacent to the current one until it finds a low spot.

Filter → Erosion → Precipitation-Based, use values:
delta: 0.25
max length: -1
connectivity: 8 way
wrap: none
passes: 3
blend: none
amount %: 50
noise: none
amount %: 1

Want more detail? Resample the surface. Surface → Resample → Simple

These are the options to use when saving visitor 3 or terrain builder readable lat/lon elevation text file.

Choose save as and select “Lon/Lat Text Mesh (*.txt)” file format. Then use Set to pixel, 0 decimal places, then if you like set output bounds min/max to elevations like -60 and 800 etc. Output bounds are minimum and maximum elevation or altitude your terrain will have.