NOAA coastline data

[Leon Gibbs]

Hi there,

 

I am really new to this and have a basic working knowledge of AutoCAD 2004.

 

Let me explain what I am trying to achieve for a start. Data I have obtained from NOAA's coastline generator needs to be tweaked for a project I am working on. I managed to get the data into Excel, then using CadTools I copied and pasted each section of the data (about 40 different objects) into CadTools and drew up 2D polylines that now form a coastline of an island and some extra smaller islands off the coast. I have now realised that the shape doesn't look right - not as oblate as it should. My source data is WGS84.

 

My question now is:

How would I make my island look the proper shape? Is it a scale issue perhaps?

 

Also, how would I go about exporting this data into a text file however in the format DMS instead of Decimla?

 

Any advice here would be greatly appreciated.

[CarlB]

I'm not familiar with NOAA coastline data, what format does it claim to be in? If WGS84 and in northings & eastings it may be accurate. Do you have any real dimensions to check it rather than just its look? If data is in latitude/longitude, how did you convert to coordinates?

 

If you have coordinates in Excel, it would seem more straightforward to convert to/create lines with DMS format within Excel, then export to a tab- or comma- delimited text file.

[Leon Gibbs]

The NOAA data I obtained was in the following format:

-46.0000 174.0000 for example.

 

It didn't specifically say that the data was WGS84. There were options to select from MapGen, Arc/Info, Matlab and Splus.

 

If you google 'NOAA Coastline' you will get the generator that I used to get the data. I used parameters as follows:

upper: -17.259

lower: -18.444

western: 177.241

eastern: 178.889

 

From this it produces a *.dat file which I opened in Excel, moved the columns so that the coordinates were lat lon (not lon lat). I then feed this into AutoCAD using CadTools and it produced polylines. Perhaps because its MapGen and not specifically WGS84 that could be why AutoCAD makes it shape look odd?

[efo]

type viewres.enter

do you want fast zooms? yes/no? of course y

than, entre the zoom percent (1-20000) (*in autocad2009 ) so entre the biggest number.

entre again....

 

may be it works, because you work on large surface...

[CarlB]

I don't know if cadTools or any other step converted from long/lat data (which is what the NOAA dta appears to be) to accurate coordinates in meters, feet, whatever. You may have to run it through a conversion process to do this. Plotting decimal lat/long would definiely give you a distortion, as a degree of latitude does not equate to the same distance as a degree of longitude (except at the equator).

[Leon Gibbs]

Is there anyway I can change the way CAD looks at the coordinates to make it think these coordinates are placed on the earth and not on a flat peice of paper (I pressume this is why CAD does this as it doesn't know that these coordinates are from the earth) ??

[Leon Gibbs]

AHA I think I know what my problem is... I have entered the coordinates in back to front... any easy was to go from lat long to long lat without re-entering everything?

[CarlB]

I think it takes a mirror of the object(s) about a vertical axis. Then maybe a rotate after that, I don't recall offhand. Then a move to get a known point back on correct coordinates.

[eldon]

To get the coordinates mirrored, this is a way I have just tried.

 

First choose one point (A) and draw a line from this point to its mirrored coordinates (A1) this should be a line at 45°. Now draw a line from the midpoint at right angles. This is your mirror line. Set MIRRTEXT to 0 so that all text keeps the right way round, and mirror all your points using the mirror line. (Just check a few coordinates to make sure)

 

But to get a proper shape, you should convert the Latitude and Longitude to UTM coordinates as CarlB says, unless you have the 3D Civil version of AutoCAD which understands Latitude and Longitude and can make the adjustments.