Basic Tiling - Achieving the Desired Maplet Overlap

(compiled by DL)

Purpose: Basic tiling allows the user to generate a suite of maplets at a higher resolution which tile a region of interest. The overlap of the new maplets is controlled by the ratio of maplet ground sample distance (GSD) to bigmap scale. This 'How-To' explains how the user achieves the desired maplet overlap percentage.

Generating a Tiling Bigmap

The user must generate a bigmap which covers the region of interest and whose parameters are set up such that the new maplets will overlap by the desired amount.

Bigmap .in File

The user must adjust the bigmap pixel scale in the tiling .in file in order to achieve the desired maplet overlap ratio. This is done by applying a multiplicative factor to the maplet ground sample distance (GSD) as follows:

Eq ol percent.png

where F is the multiplicative overlap factor, such that:

Eq ol factor.png

For example:

To achieve a 25% overlap:
- maplet GSD = 10cm
  bigmap scale = 10cm * 1.5 = 15cm

Example set of multiplicative factors:

Multiplicative Factor	Maplet Overlap	Example for Maplet GSD = 10cm
0.8	60%	bigmap scale = 10cm * 0.8 = 8cm
1.0	50%	bigmap scale = 10cm * 1.0 = 10cm
1.3	35%	bigmap scale = 10cm * 1.3 = 13cm
1.5	25%	bigmap scale = 10cm * 1.5 = 15cm
2.0	0	bigmap scale = 10cm * 2.0 = 20cm

Example BGMAP1.in (for maplets with a GSD of 10cm and a 33% overlap):

m                                   <- To locate, reference to a map
START1                              <- Reference map name
   49 49                            <- Reference map pixel/line location
   0.00013  130  1.23400  1000      <- scale (km/pixel), Q size, integer random seed, maximum maplet scale
BGMAP1                              <- bigmap name
1                                   <- bigmap program commands
.005
.025
1
0
0
1
1
1
1
1
1
0
0

A Closer Look at GSD Ratio and Overlap

GSD Ratio - Unity

GSD Ratio Unity.png

When the bigmap and maplet GSDs are equal, the maplets overlap by 50% and the outer edges of the outer maplets coincide with the edge of the tiling area.

GSD Ratio - Small Overlap

GSD Ratio small ol.png

When the bigmap GSD is greater than the maplet GSD, the maplets overlap by <50% and the outer edges of the outer maplets lie within the edge of the tiling area.

GSD Ratio - Large Overlap

GSD Ratio large ol.png

When the bigmap GSD is smaller than the maplet GSD, the maplets overlap by >50% and the outer edges of the outer maplets lie outside of the edge of the tiling area.