Helicopters, Mesh, Forests and Boots on the Ground

Why Okinawa, and why this way

Over the past few weeks I have turned Okinawa in Prepar3D v4 into something I always wanted: a living Marine Corps island. Helicopters launch from Futenma and fly real sorties. Landing zones sit in proper jungle clearings, dozens of them. The ground matches the real terrain, and the towns have buildings in them. And you already know about the ships.

I had already been working on MCAS Futenma before this, but I started delving into using AI tools for modelling, and things really took off from there. So Okinawa has turned into my testing ground, a place to experiment and redefine what is really possible now.

Here is the twist: I don’t write code. I did all of this with an AI coding partner, Claude, working on my PC. I made the calls on how things should look and fly. Claude wrote the tools, built the files, and told me what to load and test in the sim. Then I flew it, reported back, and we went again.

This post walks through what we built, piece by piece, and what I learned along the way.

HeliTraffic: helicopters that fly like helicopters

Stock P3D AI treats helicopters like airplanes. They taxi to a runway, roll down it, and ignore helipads. Old add-ons like Heli Traffic 2009 solved this for FSX, but nothing did it the way I wanted for P3D v4. So we built our own program, HeliTrafficP3D (tentatively named for now), which talks to the sim through SimConnect and flies each helicopter itself.

It started small, just to see what might be possible. The first test was an R22 on pad H1 at Futenma: spawn cold, start the engine, spin up, hover, pedal turn 360, set down, shut down. One rule I set early: no spawning aircraft that are already parked by ATC and then shut down. Every helicopter starts truly cold.

From there it grew fast:

• Pad-to-pad flights with an approach point 100 yards behind the pad, arriving slow and lined up.
• Waypoint routes, including real P3D nav points like MIXER and DUPIT, so flights from Futenma can go around Kadena instead of over it.
• Terrain following that scans the ground about a minute ahead and holds 250 ft clearance.
• Hover-taxi along the taxi lines read straight out of the airport BGL, with 90-degree turns onto each connector the way real crews do it.
• Runway-heading departures that pick the active direction from the sim wind.
• Arrival types: land and shut down, land with rotors turning, hover over the pad for a fast-rope drop, or orbit.

The fleet is now 65 helicopters in squadron liveries only: AH-1Z, UH-1Y, CH-53E, MH-60S and MH-60R, plus the MV-22B – most of these are flyable rotorcraft that operate or function as AI. Not FSX canned boring AI – we’re talking do whatever you want AI here.

Traffic mode

The heart of it is traffic mode. Each airframe has a home base and a parking spot, and it sits there cold until its sortie comes due. A sortie can make one to three stops, then it always flies home. When I start a flight near Futenma, the traffic for that base wakes up; when I leave, it goes away.

The Ready setting lets me skip the spin-up wait and watch four airframes launch one minute apart.

Ship decks

The part that gives me goosebumps is the deck work. We built a ship tool that places an LHA, LHD, LPD, LSD or ESB and records each deck spot. The approach follows the real procedure I described: a lane parallel to the ship on the port side, down to 100 ft at a point 500 ft behind the stern, a slow run up the side, then a 45-degree slide onto the spot with the nose held on the ship heading.

The first time I watched a CH-53E come up the port side of the LHA-6 and slide onto spot 4, I just couldn’t believe it. It feels like Microsoft could have done this, but they ran out of budget, and Lockheed Martin didn’t see the point. LPD and LSD decks take either two large spots or four small ones, never a mix, and the program books the deck so no two helicopters collide. Again, I have no idea how to code here, I just provide the requirements.

Photoreal patches that blend in

Okinawa now has 19 photoreal tiles, and counting. We’ll have at least 25 by the time we’re done. I download the imagery and colour-adjust each tile in GIMP. Claude builds the masks. Keep in mind most of the coverage is masked out, meaning forest and water don’t show through, so performance doesn’t suffer.

The masks were the first real win. The water mask comes from OpenStreetMap coastlines, and the photo fades out over the sea across 300 m, so reefs melt into the water instead of ending in a hard line. Every tile edge also fades over 150 m. My rule: the photoreal is patches, not the whole island, and the gaps between them have to look natural.

A few other touches:

• Sharper photos on top. My 0.27 m Futenma and Ie Shima LHD-deck images sit over the regular tiles, which turn transparent underneath.
• Clouds. Where I clone-stamped clouds out of a photo, the edited area is made see-through so the clone borders never show.
• Rivers. Visible river stretches are cut in as water, snapped to the real channel.
• A coverage map. An HTML map of every tile, updated every time an area changes, so I always know where the gaps are.

New ground under the island

Futenma always looked wrong to me. The buildings across from the flight line sat on a strange bank, and the airfield ended in a cliff. We measured it with a ground-height profile across the runway, read live from the sim. The northwest edge dropped 120 ft in 80 m, a 45% grade.

The cause was the old mesh. My FS Global 2010 ground read 15 to 35 ft off around Futenma. So we built a new mesh from the Japanese GSI 10 m elevation data. In the sim it now matches the real ground within about a foot.

It lives in two files: one for Okinawa itself, and one for the outlying islands (Kerama, Iheya and Izena, Aguni, Tonaki, Yoron). Fixes are baked straight into the main file:

• Gentle slopes blend the Futenma, White Beach and Ie Shima airfield flattens into the real terrain over 400 to 800 m, instead of walls.
• Reclaimed land at Awase and Henza is filled in, since the elevation data predates it.
• The Motobu quarry has flat floors and a level settling pond.
• A lake test at the Kin reservoir holds the water surface flat, because the data shows the old valley under it.

A side bonus: a check of every airport and LZ against the real ground turned up some that were off by up to 88 ft. Those got fixed in ADE.

Keeping the sim loading fast

With this much scenery, load times matter. So far I’ve added Windows Defender exclusions for the sim folders and raised the NVIDIA shader cache to 10 GB. Next on the list: switching to the High Performance power plan, and moving the core P3D v4 folder from my old hard drive to the SSD with a junction, so nothing has to be reinstalled.

What I learned

The biggest lesson: you don’t need to code to build serious add-ons anymore, but you do need to know what right looks like. Every good result here came from me flying it, looking hard, and saying exactly what was wrong. “The soldier’s legs slant side to side.” “There are buildings on the golf course.” “The roads through the forest are too wide.” Each of those turned into a fix and, often, a new rule for every tile.

A few other things worked well:

• Test small, then roll out. Futenma for the mesh, White Beach for autogen, one R22 on one pad for the traffic.
• Write the rules down. We keep a process document with every step and rule, so tile 19 gets the same treatment as tile 1.
• Draw in Google My Maps. Rough polygons and pins are easy for me, and the tools snap them to the photo.

What	Count
Photoreal tiles	19
Helicopters in squadron liveries	65
Landing zones imported	52
Autogen buildings	about 187,000
Vegetation areas	about 25,000

What’s next

The island is mostly built. The next stretch is about finishing it and making it consistent, so every tile looks like it came from the same hand.

Finishing the photoreal

• Bring every tile up to the current recipe. We’re running all 19 tiles through the latest masks in batches of two or three. CTA North and Camp Schwab are done. Ishikawa North and Camp Hansen are in progress. Each one then gets recompiled and reinstalled.
• Fix the seams. Once every tile is current, a seam checker will compare the overlaps between neighbours. It will flag mask disagreements, colour mismatches, cloud on only one side, and edges that fade twice.
• Colour-match the rest. Any tile not yet colour-adjusted in GIMP gets the same treatment, then a fresh woods scan.
• Apply the newest rules everywhere. Paved and bare ground inside woods stays solid photo. Smooth bright canopy, which the first scanner missed, gets picked up on the older tiles.

Finishing the autogen

• Install the latest building set. The current build is ready but not yet in the sim.
• Finish the green reviews. Trees and shrubs over the photo still need doing on a few of the newer tiles.
• Polish the look. Plainer walls on big buildings, simple boxes for odd shapes like the resort hotels, and a choice of flat or red-tile roofs per town.
• Hand-built bases. Camp Hansen, Kadena and the other bases never get generated buildings. Those will be modelled and placed by hand.

Ground, LZs and airfields

• Install the new mesh files and check them in the sim.
• Reshape Kadena and Ie Shima. Both airfield flattens sit well above the real ground. They need the same gentle-slope treatment Futenma got.
• Lakes. If the Kin reservoir test works, every reservoir gets a flat surface.
• More LZs. The remaining training-area landing zones get their ADE helipads and clearings.

Traffic and troops

• Troops in sorties. Drop-offs and pick-ups move from a keypress into scheduled traffic, with door positions for each helicopter type.
• First live Osprey flights and a final layout for the Futenma runway pads.
• Load times. Move the core sim folder to the SSD and switch the power plan.

Further out: scripted ship scenarios with AI operating from moving decks, and the F-35B doing vertical takeoffs and landing.

If you fly military helos in P3D, I’d love to hear what you’d want to see in a place like this.