The View Up Here

Random scribblings about kites, photography, machining, and anything else

Archive for September, 2014

I’m Writing Again! YAAAAY!

Posted by Tom Benedict on 15/09/2014

Rydra’s latest procedure went well. We’re still waiting on a follow-up CTA scan, but at this point she should be back on track. Both of us hope this marks the end of a three year stint of medical procedures. And we’re both looking forward to getting back to the things we love doing. For her this includes dancing, hiking, swimming, and enjoying life. For me it includes KAP, among other things.

I’ve been in a KAP dry spell for years, and it’s driven me nuts. To be fair I’ve done some KAP in the last three years, and have taken on a number of KAP-related projects during that time as well. But nothing like it was when I first started. I can’t wait to get back in the swing of things. I seriously can’t wait. And in fact, I didn’t.

Her last procedure took place on another island, so we caught an island hopper flight on Mokulele Airlines. They operate a fleet of single-engine turboprop planes that they fly around 8000′ ASL – higher than your typical KAP flight by 7500′, but a heckuvalot lower than the 35,000′ ASL of the big commercial jets. The view is fantastic. Ooooh yeah, I brought cameras. Lots of cameras. Infrared cameras and visible light cameras. And I pretended we were one super big kite, and I played!

The play had a purpose, though. One KAP project I’ve had on a back-burner for a while is to build a two-camera KAP rig so I can get R,G,B, and I channels for doing vegetation analysis and archaeology. I tried pointing my IR-converted A2200 out the window of the airplane side-by-side with my unconverted A2200. When we got back I tried aligning the images to see what I could do with them. To my delight, it worked! Here’s one pair, combined to look like color infrared film:

South Kohala Color Infrared

Combining the two a different way I got an NDVI image of the same field:

South Kohala NDVI

The cameras weren’t calibrated. I just pointed them out the window and pushed both shutter buttons simultaneously. But hey, it demonstrated that the idea works! I posted these to Flickr and to the KAP Forum, and got busy.

A couple of months ago – the last time I had time to work on this – I modified a spare Brooxes Tilt Frame to hold both the A2200 cameras. The only catch was that one had to sit a little behind the other. But since the subject distance is typically in the hundreds of feet, I figured a difference of one inch is negligible. (The cameras in the Mokulele flight were displaced by inches, and hey, they worked!)

The real trick was modifying my GentLED-CHDK cable to trigger two cameras. Around the same time I made the tilt frame, I emailed James, asking if this was possible. He assured me it was. So I got some right-angle adapter cables on Ebay and… had to drop the whole thing for several months.

Today I pulled everything out, mounted the cameras, cut the cables  to length, soldered everything together, and… Nothing.

I wrote a frantic email to James asking for help, then remembered something: Wire color coding on USB cables is random at best. I rang the cables out and found that Vcc was wired to the red wire (makes sense), but ground was wired to blue. (BLUE?! Really?!) With the correct wires connected, the cable worked fine. I tested one, then two cameras, then put the whole thing together.

IR / RGB KAP Rig

The rear camera supplies the video feed to the downlink so I can aim the cameras on the ground. The cameras are functionally identical except for wavelength sensitivity, so I can either have a color or an infrared image on the viewfinder. (Yes, I tested it both ways before flying it!) With everything working, I rushed out to give it a test flight! And… the wind died.

Most KAPers are a little more sophisticated with their kite flying than Charlie Brown, but the spirit of the thing holds true. This is how it is with KAP. As soon as your project is done, the conditions for testing it are terrible. But that’s ok. I’ve waited three years to get back in the saddle. One more day won’t kill me.

– Tom

P.S. Ok, I’m biting my nails! I can’t WAIT!

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