Project history II
And so the learning process began. I knew about latitude, longitude and a few other things but then came zenith distance, navigation triangles, assumed position, the intercept... All these were new terms with all kinds of formulae, rules, and procedures attached to them. I read about the noon sun and its special significance. At noon, the sun reaches its maximum altitude for that day and from the associated sextant measurement one can determine one's latitude via simple arithmetic. The slight problem with that is that marking the moment of noon precisely is a bit difficult in practice. Thus the next topic in my little textbook was the concept of the noon curve. Instead of making a single measurement, here one tracks the sun before noon as it rises, then after noon as it descends and extracts the peak of that curve. Having multiple measurements this is automatically more accurate than just trying to mark the moment and taking a single observation when you think you have noon.
At this point I figured that the noon curve method could be easily and rigorously implemented with Excel; after all it's just a quadratic (parabolic) fit, for which Excel is already well equipped. With that in mind I constructed the first spreadsheet, noon_curve.xls. This spreadsheet alone, however, did not quite lead me to "go public" with this project; at this point this was all still limited to my own amusement.
The idea of starting a website and making spreadsheets available to others came after some thinking about the position fix from two altitudes. The "industry standard" method of Marcq St. Hilaire known as the intercept method has proven its merits for over a century. However, what bugged me about it was its reliance on the so-called "assumed position" which was something that seemed semi-arbitrary and not very intuitively clear to me. I was certain that one should be able to calculate the crossings of the two circles of equal altitudes directly without assuming anything. Searching on the Internet revealed nothing on the subject, so I dug into the geometry of the problem, came up with a solution, which I then encoded into another spreadsheet named lops.xls (LOPs stands for two intersecting Lines Of Position marking the position fix.) I was quite sure that I was simply rediscovering something that was already known but I could not find it in any materials that I had at that moment. Now I thought that I had something other people might find useful and as a result I developed the first version of the Navigation Spreadsheets website. It was only fitting that my wife contributed to the website's design, after all this was all her fault!
The site was launched on Thursday, February 19, 2009 and not too long after that first customers began to trickle in. (to be continued)
At this point I figured that the noon curve method could be easily and rigorously implemented with Excel; after all it's just a quadratic (parabolic) fit, for which Excel is already well equipped. With that in mind I constructed the first spreadsheet, noon_curve.xls. This spreadsheet alone, however, did not quite lead me to "go public" with this project; at this point this was all still limited to my own amusement.
The idea of starting a website and making spreadsheets available to others came after some thinking about the position fix from two altitudes. The "industry standard" method of Marcq St. Hilaire known as the intercept method has proven its merits for over a century. However, what bugged me about it was its reliance on the so-called "assumed position" which was something that seemed semi-arbitrary and not very intuitively clear to me. I was certain that one should be able to calculate the crossings of the two circles of equal altitudes directly without assuming anything. Searching on the Internet revealed nothing on the subject, so I dug into the geometry of the problem, came up with a solution, which I then encoded into another spreadsheet named lops.xls (LOPs stands for two intersecting Lines Of Position marking the position fix.) I was quite sure that I was simply rediscovering something that was already known but I could not find it in any materials that I had at that moment. Now I thought that I had something other people might find useful and as a result I developed the first version of the Navigation Spreadsheets website. It was only fitting that my wife contributed to the website's design, after all this was all her fault!
The site was launched on Thursday, February 19, 2009 and not too long after that first customers began to trickle in. (to be continued)
Posted by P H at 5/14/2010 7:13 PM 
Categories: Project history
Tags: celestial navigation excel spreadsheet nautical almanac sextant Marcq Hilaire intercept
Categories: Project history
Tags: celestial navigation excel spreadsheet nautical almanac sextant Marcq Hilaire intercept
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