Re: Gridded depth data

Hi Ian,

On Friday, May 24, 2002, at 02:35 PM, ian mayo wrote:
>> The ETOPOLayer can handle 5 minute resolution data, I think you just
>> need to put those data files in the etopo directory. If you have
>> higher
>> resolution data, then some minor adjustement to the code may be
>> necessary to read them.
>
> I need to find the correct format to store them in. The files are
> downloadable in a number of resolutions, but inspecting the OpenMap code
> suggests that it's reading in the data-files as Java binary data. I
> also
> need to know how the elevations are ordered in the file.

Hmmm. I thought the etopo data we have is how it is delivered from the
source. It was a submission, and the contributor gave us the data as
well. I think the data file is ascii, like DTED. I don't know that
much about the format, though, other than that.

>
>>
>>> - Can anybody advice me on any other OpenMap data formats which would
>>> display gridded depth data?
>>
>> Once you have the elevation data, you can use the OMGrid object to
>> display it. You just need to use/create an OMGridGenerator to let the
>> OMGrid object know how to display the data.
>>
>
> I believe I can get hold of DBDB-V gridded depths, which I believe come
> as
> several directories of data organised spatially. I was quietly hoping
> there
> would be an OpenMap library capable of extracting this data to form a
> layer.

Unfortunately, there isn't. DTED and ETOPO are is the only gridded
sources we read right now.

>
>>> - Has anybody else noticed that the 5 minute ETOPO data available as
>>> part of the ETOPO download with OpenMap has the data at zero
>>> degrees longitude missing? If you switch off the graticule in the
>>> OpenMap
>>> viewer you will see the black line where the data is missing.
>>
>> Hey lookit that! That's not a bug, it's a feature.
>>
>> I'm not sure if that means data is missing, or if it has something to
>> do
>> with +- 0. Probably the latter, since in greyscale mode the line is
>> just plain grey.
>>
>
> Looking in the datafile shows that at all latitudes the value is zero. I
> presume it should take a value.

Ahh. Nice catch, I didn't get that far. I'm glad it's not an OpenMap
bug!

- Don

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Don Dietrick, BBN Technologies, dietrick@bbn.com
10 Moulton Street, Cambridge, MA 02138
617-873-3031 [fax]-2794
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