[GRASSLIST:6296] California Albers and false northing

GRASS GRASS user
1

I'm currently working on getting Landsat images for the Bay Area into GRASS 6.1cvs (Mac OS X) but I keep running into issues with the projection. I've searched the list and came up with one solution, which was to manually edit the PROJ_INFO file into this:

name: Albers Equal Area
proj: aea
ellps: clark66
a: 6378206.4000000004
es: 0.0067686580
lat_0: 0.0000000000
lat_1: 34.0000000000
lat_2: 40.5000000000
lon_0: -120.0000000000
y_0: -4000000

This returns an error saying the dataset PROJ_INFO doesn't match. Here's what the GeoTIFF contains:

name: Albers Equal Area
proj: aea
datum: nad83
a: 6378137
es: 0.0066943800
lat_1: 34
lat_2: 40.5
lat_0: 0
lon_0: -120
x_0: 0
y_0: -4000000
no_defs: defined

I've tried modifying the PROJ_INFO file to match this to no avail. I've also tried to override the projection information in the dataset with no luck (under both variants of the PROJ_INFO file).

Does anyone have any advice for working with California Albers? I'm a new user (so thanks for bearing with me).

Tim
__________________________________________
Tim De Chant
     University of California, Berkeley
     Environmental Science, Policy, and Management
     137 Mulford Hall #3114
     Berkeley, CA 94720-3114
     (510) 643-3910

2

Tim, not sure if this helps, but here goes. Whenever I use albers equal area for California, it needs to be in nad27, which has the clark 1866 ellipsoid. For nad83 stuff, I can't remember right now for sure, but I think it uses the grs80 ellipsoid. Also, everyplace that I have seen landsat data, it comes in utm, but mebbe that is just me. If it helps, the only difference btwn your proj_info file and mine is that mine specifies
datum: nad27

G'luck
-Ian

On Mar 30, 2005, at 2:30 PM, Tim De Chant wrote:

I'm currently working on getting Landsat images for the Bay Area into GRASS 6.1cvs (Mac OS X) but I keep running into issues with the projection. I've searched the list and came up with one solution, which was to manually edit the PROJ_INFO file into this:

name: Albers Equal Area
proj: aea
ellps: clark66
a: 6378206.4000000004
es: 0.0067686580
lat_0: 0.0000000000
lat_1: 34.0000000000
lat_2: 40.5000000000
lon_0: -120.0000000000
y_0: -4000000

This returns an error saying the dataset PROJ_INFO doesn't match. Here's what the GeoTIFF contains:

name: Albers Equal Area
proj: aea
datum: nad83
a: 6378137
es: 0.0066943800
lat_1: 34
lat_2: 40.5
lat_0: 0
lon_0: -120
x_0: 0
y_0: -4000000
no_defs: defined

I've tried modifying the PROJ_INFO file to match this to no avail. I've also tried to override the projection information in the dataset with no luck (under both variants of the PROJ_INFO file).

Does anyone have any advice for working with California Albers? I'm a new user (so thanks for bearing with me).

Tim
__________________________________________
Tim De Chant
    University of California, Berkeley
    Environmental Science, Policy, and Management
    137 Mulford Hall #3114
    Berkeley, CA 94720-3114
    (510) 643-3910

3

On Wednesday 30 March 2005 02:30 pm, Tim De Chant wrote:

I'm currently working on getting Landsat images for the Bay Area into
GRASS 6.1cvs (Mac OS X) but I keep running into issues with the
projection. I've searched the list and came up with one solution,
which was to manually edit the PROJ_INFO file into this:

name: Albers Equal Area
proj: aea
ellps: clark66
a: 6378206.4000000004
es: 0.0067686580
lat_0: 0.0000000000
lat_1: 34.0000000000
lat_2: 40.5000000000
lon_0: -120.0000000000
y_0: -4000000

Tim,

did you get this data from gis.ca.gov -- i.e. to old Teal Data Center GIS
warehouse?

I have had a couple of issues working with this data, but first here are the
projection parameters that are specified on their website:
http://drg.casil.ucdavis.edu/projection.html

CALIFORNIA ALBERS PROJECTION:
projection albers
units meters
1st standard parallel 34 00 00
2nd standard parallel 40 30 00
Central Meridian -120 00 00
Latitude of Origin 00 00 00
False easting (meters) 0
False northing (meters) -4000000
Datum NAD27
Sheroid Clarke 1866

...or in PROJ4 lingo :
+proj=aea
+lat_1=34.00
+lat_2=40.50
+lat_0=0.00
+lon_0=-120.00
+x_0=0.000
+y_0=-4000000.000
+ellps=clrk66
+units=m

...in summary it is a modified AEA projection, based on the Clarke 1866
Elipsoid or NAD27 Datum.

i have had best success reprojecting this data into UTM with gdalwarp:

gdalwarp -tps -e 0.0 -t_srs '+proj=UTM +zone=10 + datum=NAD83'
original_landsat_geotiff new_utm_geotiff

(see the gdalwarp man page for more details on output control. )

i then use r.in.gdal to import the UTM geotiff into GRASS.

on a side note, i am actively using a large part of the data on gis.ca.gov,
and it is always a little bit annoying to find out that most of the data is
in UTM Z10 or Z11 NAD83, while the LANDSAT and DRG are in CA_Albers with
NAD27 datum...

--
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341

4

Check out the Global Land Cover Facility
http://glcf.umiacs.umd.edu/index.shtml

You can download orthorectified landsat ETM data for anywhere in the world.
You can also download nice 30m SRTM data (90m outside the US) that you can
use for a base topographic layer. Both will import into GRASS using
r.in.gdal. They are in WGS84/UTM geotiff format. Once they are in grass, you
can r.proj to reproject them to nearly any other projection you might run
into. I just did this for one of my research areas today. I draped a band
7,5,2 rgb composite image over a 30m SRTM in NVIZ and it looked like we were
flying over it in a plane. Amazing.

Check out the VERY nice visual tutorial that comes with the current Mac OSX
binary release of GRASS.

Cheers,
Michael
____________________
C. Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
PO Box 872402
Arizona State University
Tempe, AZ 85287-2402
USA

Phone: 480-965-6262
Fax: 480-965-7671
www: <www.public.asu.edu/~cmbarton>

From: Tim De Chant <dechant@nature.berkeley.edu>
Date: Wed, 30 Mar 2005 14:30:35 -0800
To: <GRASSLIST@baylor.edu>
Subject: [GRASSLIST:6296] California Albers and false northing

I'm currently working on getting Landsat images for the Bay Area into
GRASS 6.1cvs (Mac OS X) but I keep running into issues with the
projection. I've searched the list and came up with one solution,
which was to manually edit the PROJ_INFO file into this:

name: Albers Equal Area
proj: aea
ellps: clark66
a: 6378206.4000000004
es: 0.0067686580
lat_0: 0.0000000000
lat_1: 34.0000000000
lat_2: 40.5000000000
lon_0: -120.0000000000
y_0: -4000000

This returns an error saying the dataset PROJ_INFO doesn't match.
Here's what the GeoTIFF contains:

name: Albers Equal Area
proj: aea
datum: nad83
a: 6378137
es: 0.0066943800
lat_1: 34
lat_2: 40.5
lat_0: 0
lon_0: -120
x_0: 0
y_0: -4000000
no_defs: defined

I've tried modifying the PROJ_INFO file to match this to no avail.
I've also tried to override the projection information in the dataset
with no luck (under both variants of the PROJ_INFO file).

Does anyone have any advice for working with California Albers? I'm a
new user (so thanks for bearing with me).

Tim
__________________________________________
Tim De Chant
     University of California, Berkeley
     Environmental Science, Policy, and Management
     137 Mulford Hall #3114
     Berkeley, CA 94720-3114
     (510) 643-3910