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Fun with GPT-5 and HF Propagation Analysis (Model Verification)

 

CesiumJS 3D visualization created with GPT-5 showing Gateway Vista West in magenta with the originally mis-modeled north corner, later corrected. One Maritime Plaza is modeled in green with east wall grid points and yellow corner line, plus balcony edges in green, cyan roof edge line, and orange top roof edge markers for HF propagation analysis.

Do LLMs always generate the correct set of code given their inputs? Nope. You can use the same LLM to verifiy its own outputs if we're clever about it though. Here's an example from a recent HF interference model I asked GPT-5 to build for me after a Parks on the Air (POTA) ham radio outing in downtown San Francisco. 

My first QSO perched on the edge of One Maritime Plaza was with AL7KC. That's not too surprising, I pretty regularly communicate with AL7KC. Except. It was kinda surprising because there was a skyscraper—Gateway Vista West—directly across the street between me and Alaska and about twenty-three meters away.

View from the QTH

That one little skyscraper led to a lot of fun HF propagation analysis using GPT-5. I described the area around my transmit site at One Maritime Plaza to GPT-5. I got some really interesting interference patterns based on the surrounding buildings. As I was going, I double checked GPT-5's output to make sure the buildings were where I'd said they were. I had to change a few obvious mistakes, but other than that, everything looked ok.

Then, last night, it occurred to me that I could ask GPT-5 to check its geographic model for me:



This is the resulting CZML the GPT-5 made of the points I'd asked it to model.

Top-down CesiumJS model generated with GPT-5 showing the corrected version of Gateway Vista West, magenta wall layers with green corner grid points along Washington and Battery Streets. One Maritime Plaza is also modeled with its east wall seismic ‘X’ lattice diagonal sample points in red, balcony edges in green, short cyan roof edge, and yellow vertical corner line.
Initial, incorrect, GPT-5 model of Gateway Vista West with corner extending beyond the south facing wall and structural detail on One Maritime Plaza.

Clearly, I had a few things to straighten out.

After clarifying to the LLM the coordinates of the building:

I double checked just in case this was something in the modeling code I didn't understand:


Interestingly, GPT-5 didn't confess its error this time. I carried on, asking it to make the fixes:



 and was rewarded with this mostly correct version of Gateway Vista West.

CesiumJS rendering created with GPT-5 showing corrected Gateway Vista West in magenta with aligned corner points, One Maritime Plaza east wall modeled with green balcony edges, yellow north corner line, cyan short roof edge, orange top roof edge, and red seismic ‘X’ lattice diagonal sample points, illustrating San Francisco urban HF radio propagation modeling.
Wide, corrected GPT-5 Cesium view of Gateway Vista West and One Maritime Plaza with propagation modeling features.

At which point I asked GPT-5 to put the entire model back in. Here's where I am now. I need to inquire as to why the walls on the Alcoa building are as thick with points as they are. I believe/hope that has to do with material modeling for concrete/rebar walls based on a journal article GPT-5 found, but I'll keep you posted.

Screenshot of GPT-5 output describing CZML features for HF propagation modeling in San Francisco, including TX site (white), short roof edge in cyan, east wall grid in magenta, north-building corner line in yellow, top roof edge in orange, balcony edges in green, and seismic ‘X’ lattice diagonal points in red.
GPT-5 output list of CZML features modeled in Cesium for HF propagation analysis.
Enjoyed this post? Follow along here on Copasetic Flow for more experiments with HF propagation, urban RF modeling, and GPT-5 visualizations.

Turns out the thick walls on each building were further modeling mistakes. Here's the site with all the corrections




Labels: HF propagation, GPT-5, CesiumJS, San Francisco, One Maritime Plaza, Gateway Vista West, Amateur Radio, QSO, Urban RF
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