NavList:

Jacquelin Hardy, you wrote:
"I realize now that my plan has been done already with GPS Anti Spoof Pro..."

No. Not a bit. There are many options... But you have to think up a product that might become popular in the marketplace. And although those terms (product, marketplace) sound financial, they apply equally well in an imaginary world without money. A creative work (=product) needs to find a place in the ecosystem of creative works (=marketplace). Invent. Be creative. And don't worry too much about the computaton. 

You added:
"What's left would be to draw the Mercator chart, the DR and the True Position and the celestial objects intercepts."

But is that really what's needed?? I'm not saying it isn't! Maybe it's exactly what's needed, for some parts of the market. Maybe not for real navigation. I don't know of any GPS position finding app that shows intersecting spheres representing the signals from different satellites. You get a position and an estimated error from the analysis. Shouldn't a celestial app do the same? And isn't that more fundamental than the crazy criss-crossing lines of the late 20th century intercept plot?

I have one piece of advice: make something that impresses you. If you create apps that make you happy, and if you have confidence in your creative judgement, then you'll make something that other people will like, too. This sort of advice often sounds lame, but I'm entirely serious. This works.

Frank Reed