[GRASS-user] Identification of projectiopn?

Tue Jul 5 09:48:42 EDT 2011

On Tue, Jul 5, 2011 at 1:17 PM, Rainer M Krug <r.m.krug at gmail.com> wrote:
>
>
> On Tue, Jul 5, 2011 at 1:05 PM, Daniel Lee <lee at isi-solutions.org> wrote:
>>
>> That really is a guessing game, because even if someone finds the
>> coordinates that the map could fit into, it still doesn't mean that they're
>> correct. Do you have a reason to think that the datum is WGS84? I think
>> South Africa probably uses a more accurate regional datum for local maps -
>> that makes a lot more sense unless you're working directly with web mapping
>> applications or you want to use GPS data directly.
>
> Yes - everybody is using WGS84, because it comes from a GPS - and
> reprojection usually is to be avoided because it is difficult to understand
> (I am allowed this statement - I have lived in SA and really loved it
> there!).
>
A datum commonly used in South Africa is Hartebeeshoek94, another one
is the Cape Datum coordinate system. Some topographical maps for South
Africa use a CRS with datum Hartebeeshoek94 and come together with
instructions on how to set up your GPS to use this CRS, so you don't
get lost when hiking.

IOW, at least in South Africa datums other than WGS84 are common.

>>
>> Isn't there any metadata provided with the shapefiles? I didn't know that
>> it was possible to have a shapefile without any kind of spatial reference
>> stored in the metadata. You could try making a location based on the
>> shapefile as a georeferenced file.
>
> Well - as far as I know, the projection info comes in a .prj file (missing)
> and the .shp file efectively contains the points, dbf the attribute table
> and the shx the spatial index - no metadata.
> All the data I have is the data - no metadata.
> Here is the output from ogrinfo:
> $ ogrinfo kcla_boundary.shp
> INFO: Open of `kcla_boundary.shp'
>       using driver `ESRI Shapefile' successful.
> 1: kcla_boundary (Line String)
> rkrug at ecolmod:~/Documents/Projects/HakeaLandscape/trunc/GIS/locations/Keurboom/region$
> ogrinfo -al kcla_boundary.shp
> INFO: Open of `kcla_boundary.shp'
>       using driver `ESRI Shapefile' successful.
> Layer name: kcla_boundary
> Geometry: Line String
> Feature Count: 1
> Extent: (17001.174423, -3754438.151804) - (37019.926542, -3743929.774592)
> Layer SRS WKT:
> (unknown)
> ID: Integer (8.0)
> OGRFeature(kcla_boundary):0
>   ID (Integer) = 0
>   LINESTRING (36961.220524529955583
> -3748802.374081357847899,34701.038833641323436
> -3749477.493287727236748,30885.147667205979815
> -3747804.371776290237904,26218.019240565823566
> -3746336.721327661070973,21316.066742145034368
> -3743929.774591909721494,19877.769302488635731
> -3745749.661148209590465,18821.060979475769273
> -3745544.19008540129289,17470.822566737107991
> -3746160.603273825719953,17001.174423175834818
> -3748362.078946769237518,21169.301697282135137
> -3750152.612494096625596,24368.77967529331363
> -3750181.965503069106489,26276.725258510985441
> -3751855.087014506105334,28360.788895564135601
> -3753234.678436217363924,30591.617577480181353
> -3754438.151804093271494,32323.44510686238209
> -3753674.973570805974305,27715.022698167384078
> -3751708.321969643235207,27509.55163535932661
> -3750739.672673548106104,30180.675451864066417
> -3750035.200458206236362,34025.919627271992795
> -3751737.6749786157161,37019.92654247511382 -3748861.080099302809685)
> Thanks,
> Rainer
>>
>> Best,
>> Daniel
>>
>> --
>> B.Sc. Daniel Lee
>> Geschäftsführung für Forschung und Entwicklung
>> ISIS - International Solar Information Solutions
>>
>> Deutschhausstr. 10
>> 35037 Marburg
>> Festnetz: +49 6421 379 6256
>> Mobil: +49 176 6127 7269
>> E-Mail: Lee at isi-solutions.org
>> Web: http://www.isi-solutions.org
>>
>> Am 05.07.2011 12:59 schrieb "Rainer M Krug" <r.m.krug at gmail.com>:
>> > Hi
>> >
>> > I have two shape files of which I do not know the projection (and it
>> > seems
>> > that the person I got them from does not know either...). The maps are
>> > from
>> > the Keurboom nature reserve area in South Africa (
>> > http://plak.co.za/moreinfo.php?id=347) and the two shp files have the
>> > folowing bounding boxes:
>> >
>> >
>> > In layer spatial reference system units : xMin,yMin 21340.4,-3755528.75
>> > :
>> > xMax,yMax 34244.9,-3749187.87
>> >
>> > In layer spatial reference system units : xMin,yMin 17001.2,-3754438.15
>> > :
>> > xMax,yMax 37019.9,-3743929.77
>> >
>> >
>> > I know this is a guessing game, but it must be a common projection - the
>> > map
>> > datum is very likely (almost certainly) WGS84.
>> >
>> >
>> > Any suggestions welcome,
>> >
>> >
>> > Rainer
>> >
>> >
>> > --
>> > Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
>> > Biology,
>> > UCT), Dipl. Phys. (Germany)
>> >
>> > Centre of Excellence for Invasion Biology
>> > Stellenbosch University
>> > South Africa
>> >
>> > Tel : +33 - (0)9 53 10 27 44
>> > Cell: +33 - (0)6 85 62 59 98
>> > Fax (F): +33 - (0)9 58 10 27 44
>> >
>> > Fax (D): +49 - (0)3 21 21 25 22 44
>> >
>> > email: Rainer at krugs.de
>> >
>> > Skype: RMkrug
>
>
>
> --
> Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology,
> UCT), Dipl. Phys. (Germany)
>
> Centre of Excellence for Invasion Biology
> Stellenbosch University
> South Africa
>
> Tel :       +33 - (0)9 53 10 27 44
> Cell:       +33 - (0)6 85 62 59 98
> Fax (F):       +33 - (0)9 58 10 27 44
>
> Fax (D):    +49 - (0)3 21 21 25 22 44
>
> email:      Rainer at krugs.de
>
> Skype:      RMkrug
>
>
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