Display device with stepwise display scale control, stepwise control method of the display scale on a display device, and computer program for stepwise control of the display scale of a display device

A control method of a control device, comprising:

• displaying a map on a display device;
• specifying, with a processor, an operation amount of a user operation that changes a scale of the displayed map;
• accessing, with the processor, a pre-change scale that is a scale of the displayed map before the user operation;
• and
• based on the accessed pre-change scale and the specified operation amount of the user operation, setting, with the processor, a final scale that is a value of the scale after the user operation, the by
• changing, with the processor, the scale in a stepwise manner from the pre-change scale to the final scale within a prescribed scale range, a number of steps of the stepwise change being based on a difference between the pre-change scale and the final scale, the final scale being set by:
• specifying, with the processor, a tentative final scale that is shifted from the pre-change scale by a shift amount that is based on the specified operation amount of the user;
• comparing, with the processor, the tentative final scale and a scale limit, the scale limit comprising at least one of an upper limit and a lower limit;
• setting, with the processor, the final scale equal to the scale limit when the tentative final scale exceeds the scale limit;
• setting, with the processor, the final scale equal to the tentative final scale when the tentative final scale does not exceed the scale limit;
• identifying, with the processor, a plurality of settable scales between the upper limit and the lower limit;
• calculating, with the processor, a number of the settable scales included between the pre-change scale and the final scale, the number of steps being set in proportion to the calculated number of the settable scales;
• while changing the scale, calculating, with the processor, a number of the settable scales included between a current scale and the final scale;
• and
• repeatedly changing, with the processor, the scale by a shift amount corresponding to a number that multiplies the number of settable scales included between a current scale and the final scale by a prescribed percent to change the scale in a stepwise manner until the final scale is reached.

A non-transitory computer-readable storage medium storing a computer-executable control program, the program comprising:

• instructions for displaying a map on a display device;
• instructions for specifying an operation amount of a user operation that changes a scale of the displayed map;
• instructions for accessing a pre-change scale that is a scale of the displayed map before the user operation;
• and
• instructions for, based on the accessed pre-change scale and the specified operation amount of the user operation, setting a final scale that is a value of the scale after the user operation by
• changing the scale in a stepwise manner from the pre-change scale to the final scale within a prescribed scale range, a number of steps of the stepwise change being based on a difference between the pre-change scale and the final scale, the final scale being set by:
• specifying a tentative final scale that is shifted from the pre-change scale by a shift amount that is based on the specified operation amount of the user;
• comparing the tentative final scale and a scale limit, the scale limit comprising at least one of an upper limit and a lower limit;
• setting the final scale equal to the scale limit when the tentative final scale exceeds the scale limit;
• setting the final scale equal to the tentative final scale when the tentative final control scale does not exceed the scale limit;
• identifying a plurality of settable scales between the upper limit and the lower limit;
• calculating a number of the settable scales included between the pre-change scale and the final scale the number of steps being set in proportion to the calculated number of the settable scales;
• while changing the scale, calculating a number of the settable scales included between a current scale and the final scale;
• and
• repeatedly changing the scale by a shift amount corresponding to a number that multiplies the number of settable scales included between a current scale and the final scale by a prescribed percent to change the scale in a stepwise manner until the final scale is reached.