Using Shape Files with OpenMap

[Michael]

Greetings,

I have downloaded some shape files from ESRI which I want to use in a
demo Java application using OpenMap. The problem I am having is that
the shape files are not being displayed properly by the OpenMap
MapBean. The shape files distributed with OpenMap work fine.

Is there a difference in the shape file index files with .ssx
extension vs .shx?

Since I am new to both shape files and OpenMap any help/suggestions
are appreciated.

Michael

[Don Dietrick]

Hi Michael,

mjohn...@yahoo.com (Michael) wrote in message news:<1aa764e5.02062...@posting.google.com>...

> Greetings,
>
> I have downloaded some shape files from ESRI which I want to use in a
> demo Java application using OpenMap. The problem I am having is that
> the shape files are not being displayed properly by the OpenMap
> MapBean. The shape files distributed with OpenMap work fine.

There is an entry in the FAQ on the OpenMap website
(http://openmap.bbn.com) that might explain what's happening:

http://dstl.bbn.com/dscgi/faqw.py?req=show&file=faq09.010.htp

Your shape file might contain graphics with pre-projected coordinates.
OpenMap currently only displays decimal degree lat/lon data.

>
> Is there a difference in the shape file index files with .ssx
> extension vs .shx?

The .shx file is created from the .shp file by the OpenMap ShapeLayer
code. It's a bounding box summary file to help the layer figure out
which .shp graphics apply to the current projection.

The .ssx file is a file that lists the offset of each graphic within
the .shp file.

You can use the .shx file to check to see what kind of coordinates are
in your .shp file:

java com.bbn.openmap.layer.shape.SpatialIndex -d -b <path to .shx
file>

You'll get a listing of the bounding boxes of all the graphics, and if
those coordinates aren't -90<lat<90 -180<lon<180, that's your problem.

>
> Since I am new to both shape files and OpenMap any help/suggestions
> are appreciated.

You can find more OpenMap information from the website I listed above,
which has the openmap-users mailing list archives, the FAQ, and other
documentation.

Hope this helps,

Don

=======================
Don Dietrick
BBN Technologies
dietrick at bbn dot com
=======================

[Bob Heitzman]

> > I have downloaded some shape files from ESRI which I want to use in a
> > demo Java application using OpenMap. The problem I am having is that
> > the shape files are not being displayed properly by the OpenMap
> > MapBean. The shape files distributed with OpenMap work fine.
>
> There is an entry in the FAQ on the OpenMap website
> (http://openmap.bbn.com) that might explain what's happening:
>
> http://dstl.bbn.com/dscgi/faqw.py?req=show&file=faq09.010.htp
>
> Your shape file might contain graphics with pre-projected coordinates.
> OpenMap currently only displays decimal degree lat/lon data.
>

If you have minor alignment problems make sure your data is in the
NAD83 or WGS84 DATUM as well as in Lat/Long (geographic projection).

To OpenMappers: The faq and shapefile docs do not mention which datum
is used. It is a common problem for folks to develop data based on
topo maps which are NAD27. This results is a 50+ foot shift when the
results are treated as NAD83 data.

Also the Shapefile doc mentions it uses the ordinal records to match
geographic elements to attributes. Is some rare cases there may be
deleted records in the .dbf which are just flagged as deleted but
still present. This may throw off an ordinal count if you aren't
careful. I think the address geocoding feature of ArvView 3.2 creates
some of the .dbf files with deleted records.

Something to check out anyway.

rheitzman on hot mail