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11 Inserting a Map's Image in Background
11.1 General Information About Map Images
GPS TrackMaker® uses a process of calibration with two stages:
•
In order for the program to configure a background map image correctly, it is necessary that the meridians and the
parallels be of equal distance, parallel and relatively rectilinear
•
See the figure above. The images of the item 1 are not appropriate for calibration in GPS TrackMaker®. The first
image has parallel grid lines, but note that the distance among the lines is not uniform, generating scale deformations.
The other images cannot be calibrated because the grid lines are not straight or parallel.
•
The image of the item 2 has the same scale in all its extension and the grid lines are parallel but it is not possible to
calibrate the image using two points because it is rotated. This image can be calibrated in GPS TrackMaker® but first
it must be rotated to match with the grid of the program.
•
The image of the item 3 doesn't need to be rotated and can be calibrated using two points.
•
The free version of GPS TrackMaker® doesn't rotate images. So, before calibrating, the images must be rotated in
some graphic program like PhotoPaint® or Paint Shop Pro®.
•
Big images may leave the program slow or may cause instability in the system.
•
The PC screen resolution is 96 DPI. In order for the map size to approximate the actual displayed size, you should
digitize it using a resolution close to that (ex.: 100 DPI). You should avoid resolutions above 300 DPI, because the
image size would be too large.
•
Take care when using compressed formats such as GIF or JPG. These files seem to be small when saved in disk, but
when decompressed in the memory of the computer they become very big. To know Real size of a compressed image,
export it to BMP format without compression.
•
The capacity to handle images depends on the available memory of PC. For example: a GIF image with 5MB may have
100MB after decompressed in the memory. Other programs such as MS Windows also use the available memory, so, it
would be necessary at least 256MB of memory to handle a GIF image with 5MB.
•
Monitors with resolution of 1024 x 768 pixels or above are recommended to view background images. Resolution
below 800x600 pixel is not recommended.
•
When a GTM file is saved, the images are attached to it. The images are saved in its original format; so, GIF and JPG
formats require less space than BMP in GTM file.
•
Map images with different datums must be saved in separated files.
TIP: GIF images are opened 10 times faster than JPG images but are limited to 256 colors. The GIF format is not appropriate
to aerial photos or satellite photos.
GPS TrackMaker Professional® has special tools to rotate and cut background images, accelerating the calibration
process. See the topics
Rotating Images
and
Clipping
1 – Image rotation to match the angle of the
map grid with the program grid.
2 – Image calibration with two points,
changing the position, height and width of the
image.
This method allows that many digitized map
images
backgrounds.
So, it is possible to create complete mosaics of
background images, being one of the most
important advantages of GPS TrackMaker®.
Images.
129
or
pictures
be
inserted
as
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