[Ottawa_users] New Brunswick User looking for help with GRASS and Quantum GIS - may be of interest to new users

[Alyre Chiasson]

Hello all,

Thanks for all the offers of help and the suggestion to do an initial 
post. Perhaps a quick explanation of what I am attempting to do would be 
in order as well as what resources I have on hand. I have the book, 
“Open Source GIS: A GRASS GIS Approach” by Netler and Mitasova (second 
edition, and I just got the third yesterday) and have printed out an 
“Introduction to the practical use of the Free Geographical Information 
System GRASS 6.0,” so you can point me to specific pages that might be 
of help that I may have overlooked.

I have a bunch of shape files from Environment Canada with predicted 
maximum air temperature increases for New Brunswick (they are actually 
of the whole Atlantic Region from what I can see) in 30 year blocks to 
2100 (Dataset A). They do have “prj” files. Example:

GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]

They come up as isotherms (contour lines) and are labeled; the labels 
are in a dbf file.

I also have shapefiles for the rivers and streams in New Brunswick, 
including (site/point) data with watercourse names (Dataset B). They 
also have “prj” files. They also include basic boundaries to the 
province. Again, here is the prj file.


GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]

I also have data on mean maximum water temperatures for various rivers 
across New Brunswick (Dataset C). They are current in an Excel 
spreadsheet and have the following format:


CoordinateSystem XCoordinate YCoordinate CoordinateUnits
NAD83 (CSRS) NB Stereographic 2394846.697 7657396.666 Meters


I also have upper lethal temperature data for most of the freshwater 
fish of New Brunswick. You can get predicted water temperatures by 
multiplying air temperature by 0.9 and adding it to the base water 
temperature. The idea would be for each site where baseline water 
temperatures are known, the nearest isotherm would be chosen and the 
predicted increase for that site calculated and labeled. I was also 
hoping to be able to superimpose on this a layer that would flag 
temperatures above a certain value. For example, if it happened to be 
Atlantic salmon, there would be a red dot above 24 C. Increasing red 
dots over time would means progressive loss of the species (main point 
of the exercise).

I also bought a copy of NBGEOCALC from Services New Brunswick, which 
they describe as:

NBGeocalc is a piece of software designed by SNB to help with coordinate 
conversions and transformations in New Brunswick. It is the accepted 
standard for transforming coordinates from/to ATS77 and NAD83 (CSRS). It 
is also a very useful tool to convert in all directions, latitudes / 
longitudes and UTM coordinates

I figure I might get some water temperature data from sports clubs but 
in lat and long.

 From the provincial web site I found that the province uses something 
called NAD83 (CSRS) Double Sterographic, a screen capture of parameters 
is attached (image2). I have also found that this corresponds to EPSG 
code 2953. Out of this I see two options:

1) Stick with NAD83 of datasets A and B and use GEOCALC to translate the 
coordinates of dataset 3. Other than being compatible with the province 
and I don’t know what the advantage of Double Stereographic is and maybe 
it does not make a difference for what I want to do.

2) The other option is to covert dataset A and B (shapefiles) and 
creates a LOCATION and mapset based on a Double Stereographic 
Projection. I have created a LOCATION using EPSG code 2953 and get the 
following output from g.proj.

PROJCS["Stereographic",
GEOGCS["unnamed",
DATUM["unknown",
SPHEROID["unnamed",6378137,298.257222101]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433]],
PROJECTION["Oblique_Stereographic"],
PARAMETER["latitude_of_origin",46.5],
PARAMETER["central_meridian",-66.5],
PARAMETER["scale_factor",0.999912],
PARAMETER["false_easting",2500000],
PARAMETER["false_northing",7500000],
UNIT["metre",1]]

My first concerns are the “unkown”s and the second is that the 
projection is listed as “Oblique Sterographic” and not “Double”. Maybe 
“Oblique” is actually a “Stero” projection? Somewhat disconcerting for 
someone starting out. I confirmed the EPSG code from: 
http://spatialreference.org/ref/epsg/2953/

I am also confused as to what kind of coordinate system is being used 
above (Double Sterographic). Seems like a form of UTM? As a question, if 
I was to create the LOCATION from scratch based on UTM, how would I go 
about representing New Bruswick as a LOCATION that actually physically 
lies within 2 UTM zones? All of the examples that create LOCATIONs based 
on UTM that I have seen so far are silent on what you do if your 
LOCATION covers more than one zone. Can you actually query across two 
LOCATIONs, is that the solution? So what are “Sterographic” coordinates, 
does everything become the equivalent of a single zone and the 
projection corrects for errors involved in extrapolating for what would 
be otherwise traversing from one zone to another?

Assuming that everything above is okay I grasp that I need to reproject 
the shape files and convert the coordinate system. By example, I have a 
shape file called nbmjwatr.shp and its associated prj file (first 
example above). From what I have read so far the conversion can be done 
with org2org. I am not sure what the command would be, I can’t find an 
example where the particular prj files is specified or is it 
automatically read if it is in the same directory? So would the command be

org2org nbmjwatr.shp \ -spat -60.05 35.00 -63.78 48.07 \ my_nbmjwatr.shp

?

The –spat is to cut out the boundaries to fit my the EPSG 2953 specified 
boundaries.

I have tried something similar and got a string of errors saying I 
needed to provide the transformation information. I may just have the 
wrong command. If I extract this from the top prj file above, would the 
following do the job

org2org -a_srs ‘+proj=latlong +ellps= GRS80 +datumn=NAD83’ \ -spat 
-60.05 35.00 -63.78 48.07 \ my_nbmjwatr.shp nbmjwatr.shp

?

I assume the dbf file gets imported as well. What happens to the labels 
which are in the dbf file? In the original shapefiles from Environment 
Canada the labels are missing from the upper part of New Brunswick 
because in the original they are over Nova Scotia (image1). Will the 
labels be readjusted when the original file gets clipped? I can’t fine 
anything on how label placement is determined. However, the first hurdle 
is getting the basic maps into GRASS because I don’t think Quantum can 
do the above.

I don’t know if GRASS can do the nearest neighbour isotherm type of 
calculation I have proposed above with some king of script but I will be 
doing more reading or you can suggest where I might look. Unless Quantum 
would be an easier tool to do the above, I wanted to use it mainly as a 
viewer for the resulting product.

I may be well over my head here but part of this was to see how 
difficult the whole business would be. The Open Source approach was in 
part because of my involvement with watershed groups that can’t afford 
commercial GIS software but could profit from using GIS to look at their 
data. My best course of action may be to hire someone to actually get 
the work done first (priority) and I try to duplicate it with GRASS or 
Quantum on my part. I get blank stares here when I mention either GRASS 
or Quantum or anything Linux so it would be alternative GIS software if 
I was to hire someone.

Just as background I am a biology professor of 20 years in a relatively 
small university (Université de Moncton), in New Brunswick. So I guess I 
am somewhat of an old dog trying to learn new things. The Apple IIe came 
out when I was doing my doctorate :) and I actually cut my first teeth 
on a Unix system so command lines don't bother me.

Thanks in advance for any suggestions/advice or help you care to offer. 
If this is not of general interest I can carry on by email with anyone 
that might want to help a somewhat lost soul. I guess, I am a good 
example of someone coming from outside of the specific field of GIS.

Thanks

Alyre

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