I already found a problem with this process
Unfortunately the problem is fairly fundamental. If your scenery
does not cross the boundary between UTM zones and does not cross the
equator then go ahead and use this process. Calibration errors will be less than 100 metres.
In general, UTM zone boundaries are every 6 degree longitude.
Calibration for Dummies
For those of you who are experts, please bear with me. I struggled through
a lot of the theory, so I think others who are new to scenery development
will appreciate the detail. The first part is long, and explains some
of the theory.
In the end I provide a step by step which is pretty straightforward
because it uses a spreadsheet I provide.
This process replaces task 3 in the Condor Scenery Toolkit PDF file.
This process describes how to build a CalibrationPoints.csv file to calibrate
your scenery based solely on the contents of the .hdr file produced by 3DEM
and a spreadsheet from the internet to convert UTM coordinates to latitude/longitude.
I am confident enough in the process for someone else to try it.
Let me know if it works for you.
First, lets look at an example .hdr file and talk about the SRTM3 file.
SRTM3 data has a resolution of 90 metres. That means in 3DEM
each pixel represents 90 metres by 90 metres. A Terragen tile 256x256
SRTM3 pixels, so a Terragen tile is 23,040 metres on side.
My sample scenery is 9 Terragen tiles wide and 5 tiles high.
I created it with the new version of 3DEM and the procedure which ASH33M posted late last year.
Thanks for that
So, my sample is 9*23040 == 207360 metres wide and 5*23040 == 115200 metres high.
Here is my .hdr file. map_projection tells us it is UTM Zone 18 North.
That is important for later.
file_title = EasternOntario
data_format = int16
map_projection = UTM Zone 18N
ellipsoid = WGS84
left_map_x = 367020
lower_map_y = 4947390
right_map_x = 574290
upper_map_y = 5062500
number_of_rows = 1280
number_of_columns = 2304
elev_m_unit = meters
elev_m_minimum = 8
elev_m_maximum = 771
elev_m_missing_flag = -9999
left_map_x is the UTM co-ordinate (relative to Zone 18 North) in metres of the
most east SRTM30 pixel. right_map_x is the UTM co-ordinate of the right-most pixel.
Subtract the two. You get 574290-367020 == 207270 metres. 90 metres are missing.
The same is true for Y, or north/south, 90 metres are missing.
The reason is simple (but I missed it for weeks!!). an SRTM30 pixel is 90 meters.
When 3DEM created the .hdr file it put the location in metres of the lower left
corner of the pixels.
See the attached jpg file. It depicts the 4 corners of my scenery height data.
Inside each square is the coordinates in SRTM30 pixels starting at the lower left
(0,0) to the upper right (2303,1279).
The red X's show where I want my four calibration points. At each corner
I have the UTM coordinates of the red X's and the Condor coordinates.
So far so good. Here comes the curve ball. Condor Landscape Editor origin
is the bottom right. It shows you the offset in metres from the origin
in the bottom status bar as PosX and PosY.
I need to convert the UTM coordinates of the four red X's into Condor Landscape
Editor coordinates. Here are the formulas.
CondorX = 90 + (right_map_x - UTMX)
CondorY = UTMY - lower_map_y
Based on this, convert the red X coordinates to Condor coordinates.
Here is the conversion for my example scenery.
X Y X Y
Lower left 367020 4947390 207360 0
Upper left 367020 5062500 207360 115110
Lower right 574290 4947390 90 0
Upper right 574290 5062500 90 115110
I created this table with a spreadsheet which is in the attached zip file.
The next step is to turn the UTM coordinates into latitude and longitude.
The web page http://www.uwgb.edu/dutchs/UsefulData/UTMFormulas.HTM
provides an spreadsheet to do the conversion. I made some minor formatting
changes and included it in the attached zip file. I also added some other
Condor specific bits. I take no credit for the math. I'm not that smart
The author says the conversion from UTM to LAT/LON is accurate within 10 metres.
That is more than good enough!!
So, we have everything we need. CalibrationPoints.csv file has one
line of text for each calibration point. On each line we have a location
in Condor coordinates and the latitude/longitude each seperated by commas.
My CalibrationPoints.csv is
With all of that theory behind us, here is Task 3 step by step.
Create your new scenery.
1) Start CSTLandscapeEditor tool.
2) Select File->New Landscape and load the TRN file that was saved from Task 2.
The program will automatically creates the new directory structure in
\Condor\Landscapes folder and then copies the selected TRN file to this location.
3) Do File->Save. Then File->Exit.
Create the CalibationPoints.csv file.
1) Open yourlandscape.hdr with notepad.
2) Open the spreadsheet UTMConversions1.xls.
This section is written assuming you are using openoffice.
If you have Microsoft Office I assume you know what you are
Select the "Main Page" tab at the bottom.
Scroll down to the area labelled "Condor Data".
Enter left_map_x, lower_map_y, right_map_x, and upper_map_y
from yourlandscape.hdr. Set UTM zone and North/South to values
Lower in the blue area are coordinates of the corners of yourlandscape
in UTM coordinates, Condor coordinates and in Lat/Lon.
Below that in the green area are the contents of your CalibrationPoints.csv
file. Select the light green cells and copy.
From your spreadsheet menu select "File->New->Spreadsheet".
Click in cell A1 (uppermost left cell) in the new spreadsheet.
Right click and do "Paste Special".
Un-select "Paste all" and unselect everything else under "Selection"
except "Numbers" and "Formats". Click OK.
At this point the new spreadsheet should only have four
columns and four rows of numbers. They should be identical
to the numbers in light green in the UTM1Conversions1
spreadsheet including 6 decimal places for latitude and longitude.
In the new spreadsheet do "File->Save As". Save the file
It may complain that CalibrationPoints.csv already exists. Replace it.
Close UTMConversions1.xls. If you wish, save it for the unlikely event
something went wrong.
Calibrate your scenery.
1) Start CSTLandscapeEditor tool.
2) Select your scenery in the "Landscape" pulldown menu.
Under "View/Modify" select "Calibration points".
You should see 4 calibration points listed.
Occasionally I've seen the landscape editor confused
if there are extra blank lines after the last calibration point.
Sometimes openoffice does this.
When this happens, it does not show any map or calibration points.
If you have a problem here close the landscape editor and use
notepad to remove any blank lines at the end.
3) Hit the "Calibrate" button and click yes.
4) "File->Save landscape".