I have a grib data about WRF.
The grid definition template number is 30 ( Lambert Conformal )
But now, I need to convert this lambert conformal to 0 ( Latitude/Longitude )
Is there possible?
Yes
You need to get the package wgrib2, http://www.cpc.ncep.noaa.gov/products/wesley/wgrib2/
and then just run
wgrib2 <input_file> -new_grid_winds grid -new_grid_interpolation neighbor -new_grid latlon 198:450:0.02 18:300:0.02 <output_file>
Where, of course, you need to set appropriate coordinates for your particular domain.
The coordinate definition 198:450:0.02 means:
198 -- longitude
450 -- number of points
0.02 -- grid step in degrees.
And the order is longitude, latitude.
Related
I want to check the area of geometry values.
The geometry values are POLYGON or POINT or MULTI POLYGON.
The field has the type of geometry
I check the srid of the geom field:
select st_srid(geometry)
from my_table
And I got srid=32636.
I checked here:
https://epsg.io/32636 and it seems that the units are in meters.
Now I want to get the area (in meters) of each value:
select st_area(geometry)
from my_table
And I'm getting very small values (0.0002, or 0.000097 or 0.33, ....).
I want to be sure:
Does those values means square meter (m^2) ?
So the values are less than 1 square meter ?
Since your SRS unit is metre, ST_Area will return the area in square metres. The following example calculates the area of a polygon using SRS's that have different units:
WITH j (geom) AS (
VALUES ('SRID=32636;
POLYGON((-1883435.029648588 6673769.700215263,-1883415.1158478875 6673776.142528819,-1883411.8478185558 6673765.073005969,-1883431.7724919873 6673758.967942359,-1883435.029648588 6673769.700215263))'::GEOMETRY))
SELECT
ST_Area(geom) AS sqm,
ST_Area(
ST_Transform(geom,2249)) AS sqft
FROM j;
sqm | sqft
-------------------+-------------------
237.6060612927441 | 2341.135411173445
EPSG 32636: Units are metres (Ellipsoid WGS84)
EPSG 2249: Units are feet (Ellipsoid GRS1980)
To your questions:
Does those values means square meter (m^2) ?
Yes.
So the values are less than 1 square meter ?
Yes. I'm curious about what are your geometries about. Perhaps you mixed up different SRS?
Unrelated note: Spatial operations with SRS's that have the same unit might still deliver different results, as they might also use different ellipsoids. The example below will calculate the area of the same geometry using SRS's that have metre as unit but a different ellipsoid. Note the difference in the result:
WITH j (geom) AS (
VALUES ('SRID=32636;
POLYGON((-1883435.029648588 6673769.700215263,-1883415.1158478875 6673776.142528819,-1883411.8478185558 6673765.073005969,-1883431.7724919873 6673758.967942359,-1883435.029648588 6673769.700215263))'::GEOMETRY))
SELECT
ST_Area(geom) AS sqm_32636,
ST_Area(
ST_Transform(geom,26986)) AS sqm_26986
FROM j;
sqm_32636 | sqm_26986
-------------------+--------------------
237.6060612927441 | 217.49946674261872
EPSG 32636: Units are metres (Ellipsoid WGS84)
EPSG 26986: Units are metres (Ellipsoid GRS1980)
.. but if you stick to the same ellipsoid and unit, the math makes more sense:
WITH j (geom) AS (
VALUES ('SRID=32636;
POLYGON((-1883435.029648588 6673769.700215263,-1883415.1158478875 6673776.142528819,-1883411.8478185558 6673765.073005969,-1883431.7724919873 6673758.967942359,-1883435.029648588 6673769.700215263))'::GEOMETRY))
SELECT
ST_Area(
ST_Transform(geom,2249)) AS sqft_2249,
ST_Area(
ST_Transform(geom,2249)) * 0.3048 ^ 2 AS sqm_2249, -- manually converted from sqm to sqft
ST_Area(
ST_Transform(geom,26986)) AS sqm_26986
FROM j;
sqft_2249 | sqm_2249 | sqm_26986
-------------------+--------------------+--------------------
2341.135411173445 | 217.49859674966302 | 217.49946674261872
Demo: db<>fiddle
I'm having trouble understanding what precisely the output of meshgrat means and how this relates to the lat and lon parameters of pcolorm(lat,lon,Z). I have a grid of global data, I'll call Z, at a 1.5 degree latitude x 1.5 degree longitude spatial resolution. Thus I have a matrix that's 120 x 240 (180 degrees of latitude / 1.5 = 120, 360 degrees of longitude / 1.5 = 240). Row 1 is 90 N and column 1 is 180 W (-180).
If I follow the MATLAB documentation, I can use meshgrat to produce the lat and lon arguments that I need to supply to pcolorm as follows.
latlim = [-90 90];
lonlim = [-180 180];
[lat,lon] = meshgrat(latlim,lonlim,[120 240]);
However, I don't understand why the spacing of the output is the way it is. For example, the first five values of lat are [-90.0000, -88.4874, -86.9748,-85.4622,-83.9496...]. The lon values follow the same spacing. The spacing is very close to 1.5 degrees, but it isn't. Why is there a discrepancy? The documentation claims that the paired lat and lon values are the location of the graticule vertices. In that case, these values make some sense, since there will always be one more vertex than actual grid cells. To test this, I made the following adjustment to the meshgrat code by adding one extra row and column:
latlim2 = [-90 90];
lonlim2 = [-180 180];
[lat2,lon2] = meshgrat(latlim2,lonlim2,[121 241]);
This did, indeed, produce the expected output, with the spacing now exactly at 1.5 degrees (i.e [-90.0000, -88.5000, -87.0000, -85.5000, -84.0000...]). Again, this is logical if these are viewed as vertices. But under this scenario lat and lon no longer match Z in size, which goes against how the documentation says to treat lat and lon in this case.
There seems to be a mismatch here: either the spacing in the lat lon grids are not accurate, or the girds are not the same size as the data, which would be fine in my mind as long as MATLAB knows how to interpret them accordingly, but the documentation does not seem to suggest using it this way. I have no detailed knowledge of how the MATLAB functions work at a finer level. Can someone explain to me what I'm missing?
Thus I have a matrix that's 120 x 240 (180 degrees of latitude / 1.5 = 120, 360 degrees of longitude / 1.5 = 240).
180/1.5 is indeed 120. But you also have an element at 0deg (presumably). That's 121.
I am trying to calculate distance between two geographical coordinates and I want to convert geographical coordinates to the km. Therefore I used deg2km function. However, I realise that it is not convert points properly.
For instance, I used these two points.
p_x=[5; 10]; %degree
p_y=[8; 16]; %degree
pos_y=deg2km(p_y,6378);
pos_x=deg2km(p_x,6378);
It returns as:
pos_x= [556.58549846099 1113.17099692198]
pos_y= [890.536797537587 1781.07359507517]
When I calculate distance ( sqrt((556.5-1113.2)^2+(890.5368-1781.1)^2) ) between these points I obtained distance as : 1050.2464
However I checked it google map and also other websites it should be 1042 km.
Do you have any suggestion to calculate distance and also points as kilometers properly?
Thanks in advance!
edited as :
I've points(deg)and I need to convert them km and calculate distance between points.
LAT=[41.000173;41.010134]*pi/180;
LON=[28.995882;28.995584]*pi/180;
I used this code to calculate distance. It calculates properly.
But I can not convert my points to kilometers.
LAT=[41.000173;41.010134]*pi/180;
LON=[28.995882;28.995584]*pi/180;
R=6378; %km
for i=1:length(LAT)-1
psi(i,1) = atan2( sin (LON(i+1)-LON(i)) * cos (LAT(i+1)) , cos (LAT(i)) *sin (LAT(i+1)) - sin (LAT(i)) * cos (LAT(i+1)) * cos (LON(i+1)-LON(i)) );
a=(sin((LAT(i+1)-LAT(i))/2))^2+cos(LAT(i))*cos(LAT(i+1))*(sin((LON(i+1)-LON(i))/2))^2;
c=2*atan2(sqrt(a),sqrt(1-a));
d(i,1)=R*c;
end
I have some questions about converting kilometers to geographical coordinates.
As you can see figure attached, the left one is trajectory interms of kilometers. I entered geographical coordinates and calculate trajectory as kilometers. For my calculations I need to convert degrees to kilometers. I used this code:
LAT=[41.030503; 41.048334; 41.071551 ]*pi/180;
LON=[28.999000; 29.037494; 29.052138 ]*pi/180;
for i=1:length(LAT)-1
psi_coordinate(i,1) = atan2( sin (LON(i+1)-LON(i)) * cos (LAT(i+1)) , cos (LAT(i)) *sin (LAT(i+1)) - sin (LAT(i)) * cos (LAT(i+1)) * cos (LON(i+1)-LON(i)) );
a=(sin((LAT(i+1)-LAT(i))/2))^2+cos(LAT(i))*cos(LAT(i+1))*(sin((LON(i+1)-LON(i))/2))^2;
c=2*atan2(sqrt(a),sqrt(1-a));
d(i,1)=R*c;
pos_x(i+1,1)=pos_x(i,1)+d(i,1)*cos(psi_coordinate(i,1)); %convert to kilometer
pos_y(i+1,1)=pos_y(i,1)+d(i,1)*sin(psi_coordinate(i,1)); %convert to kilometer
distance_h(i,1)=sqrt(((LAT(i+1)-LAT(i))^2)+((LON(i+1)-LON(i))^2))*1000 ; %kilometer
end
distance=sum(d);
pos_x=pos_x*1000; %convert to meter
pos_y=pos_y*1000; %convert to meter
pos_x and pos_y are ploted as circle at the figure (left).
After I calculate ship trajectory, I need to convert them degrees again.
If I use "km2deg" command I obtained my coordinates as given figure (right) and the code that I used is:
ydeg=LON(1)*180/pi+km2deg(y/1000);
xdeg=LAT(1)*180/pi+km2deg(x/1000);
But as you can see the blue line (ship trajectory) is not close to the desired path as figure given left. Normally it should be the same trend for these two plot. Because all I do is here is just converting the units. I guess I have some troubles to used "km2deg" command.
Do you have any suggestions to convert my points correctly from km to deg?
Does the following distance calculation fail to take into account the curvature of the earth?
"The deviation of STDistance() on common earth models from the exact
geodesic distance is no more than .25%. "
Docs: http://msdn.microsoft.com/en-us/library/bb933808.aspx
create proc findNearbyZips
#lat float,
#lon float,
#radius float
as
begin
declare #geo geography;
set #geo = geography::Point(#lat, #lon,4326);
with ZipsWithinRadius as
(
select zip5, city, state from zips
where
#geo.STDistance( zips.centroidGeoLocationInBinaryFormat ) <= #radius * 5280.00
)
select [...]
end
Make sure that you use the correct units so you dont calculate things in miles when it should be meters or vice versa. When in doubt, assume SI base units (http://en.wikipedia.org/wiki/SI_base_unit)