Table of Contents
TGIS_GaussianHeatmap class
DK11 for Java | tatukgis.jdk.TGIS_GaussianHeatmap | Classes | Constructors | Methods | Properties
Fast heatmap generator, creates superposition of normal (Gaussian) distribution for each data point.
Syntax
// Java public class TGIS_GaussianHeatmap extends TGIS_VectorToGridAbstract { };
// Oxygene type TGIS_GaussianHeatmap = public class( TGIS_VectorToGridAbstract ) end;
Inheritance
→ TGIS_BaseObjectDisposable → TGIS_VectorToGridAbstract
Constructors
Methods
| Name | Visibility | Description | |
|---|---|---|---|
| EstimateRadius | public | Calculates a "good choice" of the 3-sigma ("radius") of the Gaussian distribution. | |
| Generate | public | Populates a pixel (grid) layer with values resulting from computations based on the set of sample points from the vector layer. (Overrides TGIS_VectorToGridAbstract.Generate) |
|
Properties
| Name | Visibility | Description | |
|---|---|---|---|
| Coordinate | public | Defines which coordinate is taken as interpolation value if the interpolation is not based on an attribute field; default is Z. (Inherited from TGIS_VectorToGridAbstract) |
|
| DefaultValue | public | If UseDefaultValue is true, then this value will be set for each grid cell for which the interpolated value cannot be computed. (Inherited from TGIS_VectorToGridAbstract) |
|
| Radius | public | 3-sigma ("radius") of the Gaussian distribution. | |
| UseDefaultValue | public | If true, then each grid cell for which the interpolated value cannot be computed will be set to DefaultValue. (Inherited from TGIS_VectorToGridAbstract) |
|
Remarks
Method
The heat map is a method of visual presentation of spatial point data values and concentration. Mathematically it is a sum of normal (Gaussian) distributions located at each sample point with peak values representing values associated with each point.
Usage
There are three different scenarios for generating a heat map:
- heat map based on a Z, M, or Z+M coordinate value:
- set the
Coordinateproperty to the desired option - pass an empty string as the field name to the
Generatemethod
- heat map based on a attribute field value:
- pass the field name to the
Generatemethod - with the above, the
Coordinateproperty is neglected
- concentration map which means that each point has the same weight (value equal to 1.0):
- set the
Coordinateproperty to None - pass an empty string as the field name to the
Generatemethod
The resulting grid values are normalized (linearly rescaled) so they do not exceed the values of the source data (minimum and maximum grid values are the same as the minimum and maximum source values).
The resulting heatmap is highly dependent on the Radius parameter (3-sigma of the normal distribution). To easily set a reasonable value of Radius, call the EstimateRadius method before Generate. The Radius value set by the EstimateRadius method is the average of the minimal distance between neighboring points, multiplied by 3.
Pros
A quick and great looking way to present quantitative data for easy, visual analysis.
Cons
This is neither an interpolation nor an approximation method! It is suitable only for specific kinds of analysis (like a distribution of frequency of events).