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

Scott Mitchell smitch at mac.com
Wed Jan 23 13:24:17 EST 2008

Oops, by the time I wrote the rest of my last response, I forgot to  
answer the bit about crossing two UTM zones.  I have run into this,  
and saved a past email exchange on the matter - you can see it in  
convenient summary format at:



On 22-Jan-08, at 16:48 , Alyre Chiasson wrote:

> 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
> <Image1.bmp><Image2.bmp>______________________________________________ 
> _
> Ottawa_users mailing list
> Ottawa_users at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/ottawa_users

More information about the Ottawa_users mailing list