As described in http://www.polargraph.co.uk/forum/polargraphs-group2/troubleshooting-forum5/up-and-running-but-no-image-yet-thread248/

Pen size set to 0.31mm, very large grid size. The pixels are not being rendered. The pen width test completes properly, showing a range of shading. My own testing with the same settings on the firmware in question (from Polargraph 1.7.25-1.7.zip) works fine, showing a shading pattern.

See http://www.polargraph.co.uk/forum/polargraphs-group2/troubleshooting-forum5/very-large-polargraph-issues-thread265/

Solution is to change linesegs to a long

int linesegs = 1; // assume at least 1 line segment will get us there.

This shows up in the touch menu, and also causes an error to be raised and sent back to the controller when it receives a pixel to draw, and tries to work out the density.

First of all, thanks for sharing your great work.

I use the polarshield server comiled for an Arduino Mega/Ramps 1.4 configuration (with A4988 drivers installed for Y and E1)

The polargraph cotroller struggled with garbage on the COM Port. There is a bug in comms.ino in the function void comms_extractParams(char* inS). When allocating space for the string on stack there has to be room for the trailing 0 character at the end of a C-string. (strlen() does not count this).

Therefore the first line (line:191) of the function should read as char in[strlen(inS) + 1];
The subsequent strcpy(in, inS) takes care about the trailing 0 of a C-string. so that's OK then.

Just another hint: My A4988 drivers did not get enabled. In configuration.ino I had to set the last parameter of setPinsInverted(false, false, true) to false, because the signal isn't inverted.

Using RAMPS 1.4 with Arduino mega. After uploading the code to and observing the output on serial moniter gives mm per rev(default value 95) as nan. So all calculation based on it gives nan. Problem persists even after uploading machine specs.
Could it be the possible reason for machine remaining busy?

Trying to compile for MOTHERBOARD RAMPS14 with Arduino 1.8.5
Installed UTFT but UTouch was replaced by URTouch. Found older uTouch release @ https://github.com/dgolda/UTouch and installed that.

Tried both with URtouch (include URToruch.h) and uTouch but does not work.

polargraph_server_polarshield:371: error: 'LCD_TYPE' was not declared in this scope

 UTFT   lcd(LCD_TYPE, 38,39,40,41);

            ^

lcd:128: error: 'LCD_TYPE' was not declared in this scope

 byte  gap = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 10 : 10;

              ^

lcd:128: error: 'LCD_TYPE' was not declared in this scope

 byte  gap = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 10 : 10;

                                       ^

lcd:128: error: 'TFT01_24_8' was not declared in this scope

 byte  gap = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 10 : 10;

                                                   ^

lcd:131: error: 'LCD_TYPE' was not declared in this scope

 static int screenWidth = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 320 : 220;

                           ^

lcd:131: error: 'LCD_TYPE' was not declared in this scope

 static int screenWidth = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 320 : 220;

                                                    ^

lcd:131: error: 'TFT01_24_8' was not declared in this scope

 static int screenWidth = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 320 : 220;

                                                                ^

lcd:132: error: 'LCD_TYPE' was not declared in this scope

 static int screenHeight = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 240 : 176;

                            ^

lcd:132: error: 'LCD_TYPE' was not declared in this scope

 static int screenHeight = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 240 : 176;

                                                     ^

lcd:132: error: 'TFT01_24_8' was not declared in this scope

 static int screenHeight = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 240 : 176;

                                                                 ^

lcd:133: error: 'LCD_TYPE' was not declared in this scope

 static int centreYPosition = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 112 : 80;

                               ^

lcd:133: error: 'LCD_TYPE' was not declared in this scope

 static int centreYPosition = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 112 : 80;

                                                        ^

lcd:133: error: 'TFT01_24_8' was not declared in this scope

 static int centreYPosition = (LCD_TYPE == ITDB24E_8 || LCD_TYPE == TFT01_24_8) ? 112 : 80;

                                                                    ^

commented
//Uncomment the following line to use a 2.4" panel, August 2014 and later
//#define LCD_TYPE TFT01_24_8
//Uncomment the following line to use an older 2.4" panel, prior to August 2014.
//#define LCD_TYPE ITDB24E_8
//Uncomment the following line to use a 2.2" panel
//#define LCD_TYPE ITDB22

#ifndef MOTHERBOARD
//#define MOTHERBOARD POLARSHIELD
#define MOTHERBOARD RAMPS14
//#define MOTHERBOARD TFTSHIELD
#endif

//#define USE_LCD

Reported using current code from repo and hex from zip.

"I figured out the other problem.. it looks like the pixel.ino file that you have in the most recent zip file (in /arduino-source/polargraph_server_polarshield) on the website has a tiny error.

within the pixel_drawSquarePixel function the command is:
pixel_drawSquarePixel(size, size, 3, globalDrawDirection);

where I think it should be:
pixel_drawSquarePixel(size, size, density, globalDrawDirection);

That seems to make things work!

I think this one must have also been used to compile the hex, as it produced the same effect."

Will update the repo and generate new hex.