Problem reading PolygonZ shapefiles

[jxb5000]

Hello-
I am trying to use pyshp 1.1.4 Python library to read 3-D polygon
shapefiles (XYZ for each vertex).

This form of shapefile is described in "PolygonZ" section, p. 18, ESRI
Shapefile Technical Description, July 1998.

Everything is fine with 2-D shapefiles:
>>> shapes = shapefile.Reader("areas2d.shp").shapes()
(no errors here)

But with 3-D shapefile, this happens:
>>> shapes = shapefile.Reader("areas3d.shp").shapes()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/cygdrive/z/temp/pyshp-1.1.4/shapefile.py", line 310, in
shapes
shapes.append(self.__shape())
File "/cygdrive/z/temp/pyshp-1.1.4/shapefile.py", line 252, in
__shape
(mmin, mmax) = unpack("<2d", f.read(16))
File "/usr/lib/python2.5/struct.py", line 87, in unpack
return o.unpack(s)
struct.error: unpack requires a string argument of length 16

Environment details: Windows XP SP3, Python 2.5, 2-D and 3-D
shapefiles produced with GlobalMapper 12.

Thank you.

[michail xyntarakis]

Hi,

I too have found the pyshp library to be buggy.

It seems that the problem is on the following line. When you read a 2D polygon you need 2 values of eight bytes each. When you read a 3D polygon you may need 3 values.

> (mmin, mmax) = unpack("<2d", f.read(16))

If I have time I will take a closer look at the issue. By the way, how do you know that I have used the library?

Michail

[Joel Lawhead]

Thanks for the feedback. I'll look into it. If you can send me a
sample shapefile that will help. The 3D features (and the measure
features) still have some bugs as they these types of shapefile are
not as common as 2D.

Thanks,
Joel

[Joel Lawhead]

Can you send me a sample shapefile?

- Joel

[Joel Lawhead]

This problem must have something to do with reading polygon
shapefiles. I just tried the z values on a 3D bathymetry point
shapefile from the University of Hawaii and it worked. I'll keep
looking for a sample but if you all could send me one that would
really help.

- Joel

On Apr 17, 6:35 am, jxb5000 <jxb5...@gmail.com> wrote:

[jxb]

Joel- Yes, I can send a PolygonZ shapefile. Thank you for looking
into this. I am not sure how to send an attachment though. Let me
look into that....

Thanks,
John

On Apr 17, 11:36 am, Joel Lawhead <jlawh...@geospatialpython.com>
wrote:

> > Thank you.- Hide quoted text -
>
> - Show quoted text -

[jxb]

Ah, I see how to send attachment. First time on Google Groups,
sorry... I will send PolygonZ shapefile later today.

> > - Show quoted text -- Hide quoted text -

[Joel Lawhead]

Thanks!

--
Joel Lawhead, PMP
NVision Solutions Inc.
Phone: 228-242-0014
Fax: 228-242-0013
Cell: 228-342-1891
Email: jlaw...@nvs-inc.com
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