All maps distort things -- one or more of area, shape and distance. They [splatten] a roundish sphere into a flat piece of paper. Some distortions are much worse than others. The Cahill-Keyes projection is the best invention to date we humans have for minimizing the effects. Unfortunately very few know about it or have seen it. This map by Duncan Webb of Australia, possibly the first modern full scale version of the CK map projection could go a long way to rectify our common (mis)perception of the relative shapes and sizes of where we live. If it sees production …continue.
….some further experiments with
geoprocessing. Here is a simple script to convert a bunch of coverages
to shapefile. There are 9 coverages occupying 3mb, it takes about 6
minutes, consumes 2 processors to 80-90% capacity and chews through
300mb of ram:
cd w:/Env-dat.003/2007-March/workspace/envy_ed2import arcgisscripting
gp = arcgisscripting.create()
gp.Workspace = ‘./’
todo = !dir /b fwtc*
for cov in todo:
gp.FeatureClassToShapefile( cov + ‘/arc’, ‘./shp’)
Contrast that to using
which takes 10 seconds:
for %a in (fwtc*) do ogr2ogr -f “esri shapefile” ogr\%a %a
The problem is, ogr2ogr doesn’t …continue.
I think my python-COM environment is messed up.
D:\> python list-fc.py
and expectedsomething like
- using Mark Cederholm's
recipe requires registering com stuff, which conflicts wth
PythonWin's com stuff.
- I'm using Arcgis with python
instead of the shipped 2.5. This hasn't proved problematic before,
but maybe I just haven't wondered into this section of the forest
before (which means I need to eat crow for Jason
- I have concurrent python 2.5 and python 2.6 …continue.
by a conversation with my father eons ago, I'm researching and
experimenting how to create a map in a discontinuous or interrupted
projection. Initially I was thinking of Buckminster Fuller's Dymaxion
Map, but I've since chosen a variant of the Bernard J. S. Cahill's
the Cahill-Keyes M-style.
I've successfully recreated the single octant and eight octant Open
Office drawings from the macros and instructions provided. It took a
couple of hours because I had to figure out how OO macro dialogs work,
and don't. There were some errors at the beginning that went away by
themselves -- which always make me nervous because one is never sure if
one day they might also decide to come back by themselves! I used OO
v3.2 on linux so that may have contributed to the difficulty.
Results are at
(download using [get source] link at right)\
Anyway, the upshot is now I have a practical understanding of …continue.
In the spring of 2007 the Natural Resources Department of Canada
released digital topographic data for the whole nation under a free and
policy. The product is
For bulk downloads, see
(subst http for ftp if that is more to your liking).
Although the data has been out for 5 months or so, as near as I can tell
it has yet to be used in any significant public way (no one has been
yapping about it outside the confines of their cubicle). The sole
reference I could find is Stewart Russell’s my neighborhood, according
A modest project to be sure, but I’m happy to see the first one …continue.
After a lot of hairpulling and asking smart people for help (Mark
Cederholm, Kirk Kuykendall) I have a working python script which
searches a file geodatabase and changes the AliasName of the matching
feature classes from the incomprehensible BS_1370009_2 to the
human friendly Residential Area
. It does the same for a subset
of the attribute names.
AlterAlias.py can be nabbed from my bitbucket canvec
It relies on
(necessary portion of which is bundled as parco.py)
I took the route of changing the aliasname instead of the fc_name to
make it easier, I hope, to automatically incorporate the twice annual
2007 September 07
A free Canada-wide 1:50,000 elevation model.
This project was in preparation of sending a Canada-wide elevation model
to Google Earth and NASA World Wind. It was completed a couple of years
ago, although the data is not yet generally available through those
tools — thus the reason for hosting it
(thank you Adam
and the Free Earth Foundation!).
note: hostname has changed
The data are marked draft because only a very preliminary review of the
resulting mosaick has been done. There is no guarantee the data is
complete or faithfully represents it’s source. I am interested feedback
on the product and it’s utility but I make no promises …continue.
This was an attempt to use some photographic image processing
to bring back some detail in the regions of mountain shadows in a
Landsat7 composite image. It didn’t work but I learned a lot in the
process. It could be useful in future with other data which is has not
lost so much to white and black shadows.
Original on left while right shows result of contrast mask combined
with grain merge selected in the layer Mode. It almost works, but
not enough for the project I was researching for. Below, detail view of
grain merge result.
matt wilkie wrote:
just found the PHATCH project,
is python alternative to …continue.
As Tom Patterson describes in “Resolution bumping GTOPO30 in
using a too-detailed shaded relief image can actually yield a map which
is less legible. In the same article Patterson also demonstrates how to
counteract this problem. He says this is something to do to the
elevation model and not the shaded relief, but not having a graphics
program installed on my machine capable of editing 16 bit images I
applied it to the shaded relief instead. The results are good, but I’m
itching to try it out properly to see what the difference is when used
earlier in the chain. Here is my nutshell re-work of Patterson’s
resolution bumping …continue.