Dredging Committee Update
Jim Starkey
I eventually did find a suitable open source coordinate conversion package suitable for massaging the CLE pre and post dredging survey data, which is now all converted into a form suitable for the Harbor Model software (see below if you care). Next week I will be adding the odd bell and whistle to the software to perform the necessary and appropriate analyses of our harbor bottom projections to reality. Once that is done I will undertake the arduous task of scheduling a Dredging Committee meeting. In addition to a data discussion, Bion would like to start a dialog about how to replace moorings after the next dredging. I have some thoughts on the subject, but I'll wait for the meeting.
Mory came up with what I think is a rather splendid idea, which is that we put together an inexpensive, portable harbor survey box that would let us to period free harbor surveys. In its simplest form, the box would a depth sensor, a GPS, and a Raspberry Pi in a waterproof box, maybe with separate display. To do a survey, all we would have to do is attach it to a transom of small boat and drive around the harbor collecting data points. The screen could show collected data points as guidance for the next pass. The tidal correction could be added at the time of the measurement or after the fact. I have most of the necessary parts in inventory and will put a box together. Sounds like fun.
I'll be in touch next week about a data/time for the next meeting.
[You can stop reading if you wish]
The coordinate problem is that the Harbor Model Software is designed around latitude/longitude while the CLE data uses the Massachusetts State Plane Coordinate System, Mainland Zone, as do all other local GIS applications. The problem is latitude/longitude are suitable, in fact essential, for spherical geometry but a real PITA for local geographical usage. The state coordinate system, which goes back to 1933, defines one or more coordinate systems per state that map latitude/longitude into a simple square grid with an accuracy of at least 1 in 10,000. This means there are hundreds of grid systems, each tailored to a particular state or region. Each involves significant messy math. The following defines our local state coordinate system:
Projection: Lambert Conformal Conic
Spheroid: GRS 80
Central Meridian: -71.5
Reference Latitude: 41
Standard Parallel 1: 41.71666666667
Standard Parallel 2: 42.68333333333
False Easting: 200000
False Northing: 750000
As a result, GIS conversion packages are complex (to handle, literally, hundreds of conversion types) and, generally, expensive. I audition quite a few packages before I found one that was a) suitable, b) working, and c) free.