| Author | Message | ||
     Ted Lavino Senior Member Username: Tlavino Post Number: 432 Registered: 01-2004 |
Hi Mark, looks like I discussed your second question, but not your first... From the Introduction in Chart #1: "Shoreline-Shoreline shown on charts represents the line of contact between the land and a selected water elevation. In areas affected by tidal fluctuation, this line of contact is usually the mean high-water line. In confined coastal waters of diminished tidal influence, a mean water level line may be used...." There's also a nice picture in section of all the heights and depths in H-20,,, There is also a short blurb in Bowditch paragraph #335 (Heights), but adds little to the info in the Chart #1 intro. | ||
| Mark Howe Moderator Username: Unclemark Post Number: 231 Registered: 08-2003 |
Thanks Ted; I checked your link but never could find a definition of chart datum and land datum. I found I-15 a bit more helpful in defining the green area as "drying height above chart datum" but no definition as to the upper extent of that [I assume MHW or Sea Level]. Have you found anything? BTW I am a fanatic on GIS but severely limited in my abilities on the computer end. Fortunately I got John Fellner in the class to help me out. :-) I tried to down the rasters but ran into problems; can't recall what. I'll try again. | ||
| Ted Lavino Senior Member Username: Tlavino Post Number: 430 Registered: 01-2004 |
Hi Mark, you might want to check out a series of links I did some time ago in Electricmarine Discussion Board » All Aspects of Sailing » Navigation » Navigation Publications listing links for most of the available navigation publications from the US government (NGA, USCG and NOS). Specifically for Chart #1, here is the link allowing you to downlaod an electronic copy of Chart #1 in Adobe Acrobat (PDF) format. http://www.nga.mil/portal/site/maritime/?epi_menuItemID=dd3a68b9bd9716625b2a7fbd 3227a759&epi_menuID=35ad5b8aabcefa1a0fc133443927a759&epi_baseMenuID=e106a3b5e50e dce1fec24fd73927a759 If you don't have an view supporting PDF files you can download one from Adobe at http://www.adobe.com/ and click on the "Download Acrobat Reader" button. BTW did you mange to down the raster charts and chartplotting application that Maptech is now posting without charge? What do you think of the GIS class? | ||
| Mark Howe Moderator Username: Unclemark Post Number: 230 Registered: 08-2003 |
Hi Ted; Is there an online link? :- (slightly embarrassed smiley face because I'm asking Ted for a link I can click.) | ||
| Ted Lavino Senior Member Username: Tlavino Post Number: 429 Registered: 01-2004 |
Hi Mark, I think you're referring to areas that are handled with a green tint, like those found in section C32-34 of Chart #1 | ||
| Mark Howe Moderator Username: Unclemark Post Number: 228 Registered: 08-2003 |
There is a bunch of stuff on Navigation on the Sailing board. But since this is a general question I am posting here. A navigation chart uses MLLW as its datum for depths. What does it use for the line that outlines the land? I would hope it would be MHW [sea level] because that would make the most sense, but then there would be the problem of how to deal with the area in between the chart zero datum and the land zero datum. This would be most important in places with large areas of intertidal land, marshes, etc. Anybody have experience with this? | ||
| Mark Howe Moderator Username: Unclemark Post Number: 229 Registered: 08-2003 |
A navigation chart [on the west coast] uses MLLW as its datum for depths. What does it use for the line that outlines the land? I would hope it would be MHW [sea level] because that would make the most sense, but then there would be the problem of how to deal with the area in between the chart zero datum and the land zero datum. This would be most important in places with large areas of intertidal land, marshes, etc. We had extensive discussion on this at some point and I cannot find it. But that was dealing with hazards falling into that zone; here I am thinking of the general intertidal topography. Anybody have experience with this? Anybody know where our discussion on this is? |
