State tax filing

Since you are working out of the NY office when you do work on location, it would seem that you would not meet the convenience of the employer rule and all of your income would be subject to NY state taxes.

In order to meet the convenience of the employer rule it would need to contain or be near specialized facilities that cannot be made available at the employers place of business or four of the following;

• Home office is a requirement of employment
• employer has a bona fide business purpose for your home office location
• You perform some of the core duties of your employment at your home office
• You meet or deal with clients regularly at your home office
• Your employer did not provide you with a designated office space
• Your employer reimbursed your home office expenses

AND three of the following:

• The employer maintains a separate telephone line and listing for the home office. 
• The employee’s home office address and phone number is listed on the business letterhead and/or business cards of the employer. 
• The employee uses a specific area of the home exclusively to conduct the business of the employer that is separate from the living area. The home office will not meet this factor if the area is used for both business and personal purposes.
• The employer’s business is selling products at wholesale or retail and the employee keeps an inventory of the products or product samples in the home office for use in the employer’s business. 
• Business records of the employer are stored at the employee’s home office. 
• The home office location has a sign indicating a place of business of the employer. 
• Advertising for the employer shows the employee’s home office as one of the employer’s places of business. 
• The home office is covered by a business insurance policy or by a business rider to the employee’s homeowner insurance policy.
• The employee is entitled to and actually claims a deduction for home office expenses for federal income tax purposes.
• The employee is not an officer of the company.

If you do NOT meet the above criteria, then your full income from NY should be included on your Non Resident return.