Keywords: thermal, dynamic maps
Summary
This demo shows how to use a raster image to define the temperature of an object. In addition to including a static scenario (temperatures that do not vary with time) this demo includes a dynamic scenario where the temperatures vary with time using a series of raster images.
Details
Like many of the other map types available in DIRSIG, a temperature map leverages a raster image file to drive a material property. In this case, that property is the temperature. The user can drive the temperature using either a floating-point image (single- or double-precision with an ENVI header) that specifies the absolute temperature (in Celsius) directly or as an 8-bit image (as a TIFF, JPEG, PNG, etc.) with a gain and bias to scale the values into degrees Celsius. This example uses 8-bit PNG image files to define the temperatures.
This demo contains two separate simulation configurations:
-
A static simulation using a single raster image, which results in temperatures that are constant with time.
-
A dynamic simulation using multiple raster images, which results in temperatures that vary with time.
Important Files
The scene in this demo is composed of a box placed on a background. The flat background is assigned material ID #1 and it is configured to use the THERM temperature solver. In contrast, the box is assigned material ID #2 and the temperature will be driven by a raster image map.
Material Setup
Although temperature maps can be defined in the scene file, a
temperature map is actually a specialized Temperature Solver
and the preferred method for configuring it is via the material
file. The entry for the box material (ID = 2) from the demo/static.mat
material file is shown below:
MATERIAL_ENTRY {
ID = 2
NAME = Box
EDITOR_COLOR = 0, 1, 0
TEMP_SOLVER_NAME = Map
TEMP_SOLVER {
IMAGE_FILENAME = hot_spot.png
DRAPE_PROJECTOR {
INSERT_POINT = -5, -5, 0
GSD = 0.10
ORIGIN = IMAGE
FLIPX = FALSE
FLIPY = FALSE
EXTENDX = MIRROR
EXTENDY = MIRROR
}
OPTIONS {
GAIN = 0.1
BIAS = 40
}
}
RAD_SOLVER_NAME = Classic
RAD_SOLVER {
ENABLE_SAMPLED_DIFFUSE = FALSE
}
SURFACE_PROPERTIES {
EMISSIVITY_PROP_NAME = ClassicEmissivity
EMISSIVITY_PROP {
FILENAME = black.ems
SPECULAR_FRACTION = 0.0
}
}
DOUBLE_SIDED = FALSE
}The key to the configuration is the Map keyword assigned to the
TEMP_SOLVER_NAME, which indicates we want to use the temperature
map solver. The corresponding TEMP_SOLVER section contains the
configuration of the map including the raster image filename (see
the IMAGE_FILENAME variable), the image projection information
(see the DRAPE_PROJECTION section) and the options to scale the
raster image pixel values with a gain and bias (see the OPTIONS
section).
|
Note
|
The default GAIN and BIAS are 1 and 0, respectively. |
The box in the scene is 10 x 10 x 10 meters and centered at the scene origin (0,0). The drape projector is setup to project the 100 x 100 pixel raster images onto that box using a GSD of 0.1 (which scales the images to 100 * 0.1 = 10 meters) and an offset of -5,-5 meters (which moves the image origin to the lower-left corner of the box’s top surface).
Static Scenario
The static scenario is defined by the temperature map configuration in
the materials/static.mat file. In this case, the IMAGE_FILENAME
variable is assigned the name of an 8-bit, PNG raster image file and
the supplied gain and bias options scale those temperatures into
degrees Celsius:
TEMP_SOLVER_NAME = Map
TEMP_SOLVER {
IMAGE_FILENAME = hot_spot.png
DRAPE_PROJECTOR {
...
}
OPTIONS {
GAIN = 0.1
BIAS = 40
}
}The single 8-bit PNG image used is shown below. The peak digital count (DC) in the image is 250, which corresponds to a temperature of (250 * 0.1) + 40 = 65 C.
Dynamic Scenario
The dynamic scenario is defined by the temperature map configuration in
the materials/dynamic.mat file. The key difference is passing the
IMAGE_FILENAME variable the name of a temporal image list (TIL) file:
TEMP_SOLVER_NAME = Map
TEMP_SOLVER {
IMAGE_FILENAME = hot_spot.til
DRAPE_PROJECTOR {
..
}
OPTIONS {
GAIN = 0.1
BIAS = 40
}
}|
Important
|
The .til file extension is specifically reserved for
these temporal image list files. Failure to use this
extension will result in the code trying to find the
appropriate image file reader instead of treating it
as TIL. |
The contents of the maps/hot_spot.til file specify a series of image
files to be used as a function of time:
0.0 hot_spot_000.png
1.0 hot_spot_020.png
2.0 hot_spot_040.png
3.0 hot_spot_060.png
4.0 hot_spot_080.png
5.0 hot_spot_100.pngThe first column is time (in seconds) since the simulation reference time. The second column is the name of the image file to be used. This series of files will be used in the following manner:
-
Any times before the first time will use the first file.
-
Any times after the last time will use the last file.
-
The first file is used until the time corresponding to the second tile is reached. There is no temporal interpolation of the image data.
In this simulation, the six image files have a simple "hot spot" that slowly increases in magnitude. Note that the same gain and bias values are used for all the images in the temporal image list.
Setup
Static (single-frame) Simulation
To run the static, single-frame simulation, perform the following steps:
-
Run the DIRSIG
demo.simfile -
Load the resulting
demo-t0000-c0000.imgfile in the image viewer.
Dynamic (multi-frame) Simulation
To run the dynamic, multi-frame simulation, perform the following steps:
-
Run the DIRSIG
video.simfile -
Load the resulting
demo-t0000-c0000.img,demo-t0000-c0001.img, etc. files in the image viewer.
This simulated collection spans 6 seconds, which is the entire duration of the temporal map sequence.
Results
Static (single-frame) Simulation
The static, single-frame simulation produces a single image frame.
Dynamic (multi-frame) Simulation
The imaging instrument is setup to use the "file per capture" output schedule. As a result, the simulation produces 6 separate image files for the 6 captures. The animation below was created from these 6 frames.
